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Comparative Vertebrate Anatomy

by: Peyton Schimmel

Comparative Vertebrate Anatomy ZOO 3713

Marketplace > University of Central Florida > Animal Science > ZOO 3713 > Comparative Vertebrate Anatomy
Peyton Schimmel
University of Central Florida
GPA 3.65

Frank Logiudice

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Frank Logiudice
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This 74 page Class Notes was uploaded by Peyton Schimmel on Thursday October 22, 2015. The Class Notes belongs to ZOO 3713 at University of Central Florida taught by Frank Logiudice in Fall. Since its upload, it has received 9 views. For similar materials see /class/227480/zoo-3713-university-of-central-florida in Animal Science at University of Central Florida.

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Date Created: 10/22/15
Chapter 15 The Urogenital System A The Urinary System 1 The Kidneys and Their Ducts a The Basic Pattern of the Archinebhros 1 Vertebrate kidneys have a basic architecture of glomeruli renal tubules and a pair of excretory ducts a Differences between the vertebrate classes are basically in the number and arrangement of glomeruli and in the complexity of the renal tubules 2 The Glomerulus aka Renal Corbuscle is composed of a cup shaped portion of the renal tubule called the Bowman sGlomerular Capsule and a specialized capillary bed called the Glomerular Capillaries a It serves as the initial site of urine formation It is where the filtration of blood occurs b The glomerular capillaries are a specialized capillary bed 1 They receive blood from the Afferent Arteriole and drain into the Efferent Arteriole instead of a venule a The two arterioles regulate blood pressure within the glomerular capillaries which in turn regulates filtration pressure and urine formation b The efferent arteriole will give rise to its own capillary bed which is also associated with the renal tubule 2 The glomerular capillaries have numerous pores or fenestra along their lengths which form one component of the Filtration Membrane 3 The glomerular capillaries may or may not be associated with Bowman s capsule a In the primitive state glomerular capillaries are suspended in the coelom by peritoneal folds and discharge their filtrate directly into the coelomic fluid 1This fluid is then picked up by a funnelshaped structure called a Nephrostome which leads into the renal tubule 2 This type of glomerulus is called a External Glomerulus b In the more advanced condition the glomerular capillaries are ensheathed by Bowman s capsule 1This type of glomerulus is called a Internal Glomerulus c Bowman s capsule is a hollow cup shaped segment of the renal tubule 1 It is the initial segment of the renal tubule 2 It is a two layered structure a The outer layer is termed the Parietal Layer and consists of a simple squamous epithelium b The space between the inner and outer layer is called the Capsular or Urinary Space because this is where the initial stage urine accumulates after filtration c The inner layer is a specialized epithelium in intimate contact with the glomerular capillaries 1This inner layer is termed the Visceral Layer 2 The specialized epithelial cells are called Podocytes a The podocytes have numerous foot like processes that wrap around the glomerular capillaries and form one more component of the filtration membrane 3 During development the renal tubules differentiate from a pair of ribbons of embryonic mesoderm a This mesoderm is called Intermediate or Nephrogenic Mesoderm 1 It is located lateral to the mesodermal somites and extend the length of the trunk from the head to the cloaca b The first tubules appear at the anterior end of this Nephrogenic mesodermal ribbon 1 New tubules will appear as the trunk lengthens 2 The paired longitudinal ducts begin development as caudally progressing extensions of the first tubules a The two ducts will grow caudally until they reach the cloaca c Due to their origin against the mesodermal somites which give rise to the back muscles the kidneys will be retroperitoneal 4 In the typical vertebrate kidney several renal tubules will drain into one Collecting Tubule a The collecting tubules will ultimately drain into the paired longitudinal ducts which in turn will drain into the cloaca or its derivative 5 The renal tubules will increase in complexity among the vertebrates a They are short and straight in agnathans b They are long and highly convoluted in mammals and show a great degree of regional specializations 6 The Nephron is the functional unit of the vertebrate kidney a A nephron is defined as a renal tubule and its associated blood vessels 1 The production and refinement of urine requires a close association between the renal tubules and the blood b Nephrons perform three actions in the production of urine 1 Filtration is the first step and occurs in the renal corpuscle a The result called Glomerular Filtrate needs to be greatly refined 2 Tubular Resorption is the recovery of elements of filtered material from the glomerular filtrate by the blood a This occurs along the rest of the length of the renal tubule b Material is moving from the renal tubule into the blood 3 Tubular Excretion is the dumping of more waste substances into the glomerular filtrate from the blood a This occurs along the rest of the length of the renal tubule b Material is moving into the renal tubule from the blood 7 Archinephros is the term for the hypothetical ancestral vertebrate kidney a Today the closest ting to the Archinephros is found in larval hagfish 1 Their kidneys have a transient series of segmental external glomeruli nephrostomes and tubules formed throughout most of the nephrogenic mesoderm a This type of kidney is called the Holonephros 2 The larval hagfish holonephros will develop into a Mesonephric kidney during development b Types of Kidneys 1 Pronephros a The pronephros are the first kidneys b Pronephric tubules arise first from the nephrogenic mesoderm 1 They appear at the cranial aspect of the nephrogenic ribbon a This portion of the nephrogenic mesoderm is termed the pronephros 2 The pronephric tubules are segmental a They are arranged with one pair per somite in this region of the trunk 3 Pronephric tubules arise as solid aggregates of nephrogenic cells that organize into a number of lumens and nephrostomes a The development of the nephrostome does not occur in mammals and birds 4 ln fishes and amphibians each pronephric tubules will have an external glomerulus associated with it a In dipnoans and larval urodeles and anurans the first 2 or 3 external glomeruli will coalesce into a single large glomerulus and capillary bed 5 The number of pronephric tubules is always low a Ex 7 pairs of pronephric tubules appear in the human embryo c The distal portions of the first few pronephric tubules will unite to form a pair of caudally directed ducts which will grow to the cloaca 1 These ducts are the right and left Pronephric Ducts aka Archinephric Ducts 2 The two pronephric ducts and the pronephric tubules make up what is termed the Pronephric Kidneys d Pronephric tubules are temporary structures 1 More complicated urinary tubules will form caudally and the pronephric tubules will regress 2 The pronephric duct however does not regress a Instead it remains to drain the next set of urinary tubules the Mesenephric Tubules 2 Mesenephros a The right and left pronephric ducts will have an inductive effect on the nephrogenic mesoderm causing the formation of a new set of urinary tubules the Mesenephric Tubules 1 With the regression of the pronephric kidney and the development of the mesenephric tubules the pronephric duct will become the Mesenephric Duct aka Archinephric Duct a The mesenephric tubules and mesenephric ducts make up the Mesenephric Kidneys 2 The transition from pronephros to mesenephros is gradual a In the transition zone between the two sets of tubules the tubules will be segmentally arranged b In reptiles amphibians and reptiles the mesenephric tubules will initially have open nephrostomes 1These open nephrostomes will close later in the lives of amphibians reptiles and most fishes a However some fishes retain the open nephrostomes throughout life c The mesenephric tubules of embryonic birds and mammals lack the open nephrostomes 1The nephrostomes are always closed even from the start d One notable difference between the pronephric tubules and the mesenephric tubules is that pronephric tubules are distributed at a ratio of one pair per body segment while mesenephric ducts are much more prolific being arranged as 2 or 3 pairs per body segment b The Mesenephric Kidney in Agnathans 1 The mesenephric kidney differs between hagfish and lampreys 2 In adult hagfish the mesenephric kidneys are modifications of the holonephric kidney of the larval hagfish a These modifications include 1 All of the nephrostomes close 2 The mesenephros are segmentally arranged with 30 to 35 renal corpuscles attaching to the mesenephric duct by short tubules a Flanking the mesenephros will also be degenerating renal corpuscles b The adult hagfish kidney also lacks peritubular capillaries and a renal portal system 3 The lamprey kidneys are long thin folds running about half the length of the coelom a It has a mesenephric duct and large renal corpuscles that out number body segments b It lacks peritubular capillary beds and a renal portal system c The Mesenephric Kidnevs in Fishes and Amphibians 1 The mesenephros of jawed fishes and amphibians is sometimes referred to as the Opisthonephros meaning rear kidney a The reason behind this terminology is that the mesenephric tubules develop as far caudally as the cloaca b Some of the more anterior mesenephric tubules in males will become modified to carry sperm from the testis to the mesenephric duct by way of the kidney 1These tubules will grow into the nearby embryonic genital ridge during development a The genital ridge is an elevation of mesoderm that will give rise to the gonads in this case testes 2 These tubules are termed the Vasa Efferentia 3 This portion of the male kidney that carries sperm instead of urine is termed the Sexual Kidney a The portion of the mesenephric duct that drains the sexual kidney is called the Epididymis 2 The mesenephric duct of fish and amphibian kidneys is often supplemented or even replaced by Accessory Urine Ducts which will also carry urine d The Mesenephric Kidnev in Amniotes 1 The mesenephros is the functional kidney only in the embryonic and fetal amniote a During this time when the mesenephros is the functional kidney a new kidney called the Metanephros begins to form 1The mesenephros will regress when the metanephros becomes functional 2 Some remnants of the mesenephric kidney is still found in adult amniotes a The mesenephric duct will remain as a sperm carrying duct in the male b The mesenephric duct will remain as a series of blind tubules in the ovarian peritoneal folds of females 1They are called Eoophoron Gartner s Duct and Paroophoron 3 The Metanepheric Kidney a The metanephric kidney is the functional kidney of amniotes b The metanephric kidney develops from the caudal end of the nephrogenic mesoderm 1 This portion of the nephrogenic mesoderm will detach from the rest and migrate cranially 2 Formation begins when a Metanephric Bud grows from out of the caudal end of the mesenephros and becomes surrounded by the caudal portion of the nephrogenic mesoderm a This portion of the nephrogenic mesoderm will develop into the parenchyma of the kidney ie the cortex and medulla b The stalk connecting the metanephric bud to the mesenephros will develop into the Ureter and the Renal Pelvis 1 In most amniotes the ureters will eventually detach from the mesenephric duct and attach directly to the cloaca a In some lizards and sphenodons the mesenephric duct is never lost c The Structure of the Metanephric Kidnev 1 The kidney is broken up into three regions which are asymmetrically arranged Cortex Medulla and Pelvis a The cortex is the outermost portion of the kidney 1 It contains the renal corpuscles 2 The cortex will have extensions running into the medulla called the Renal Columns or Cortical Columns a These extensions will divide up the medulla into functional lobes 3 It develops from the caudal portion of the nephrogenic mesoderm b The medulla is the middle layer 1 It contains the collecting ducts and the portion of the nephrons which are called the loops of Henle 2 Due to the renal columns the renal medulla is divided into a number of triangular segments termed renal Pyramids or Medullary Pyramids 3 It also develops from the caudal portion of the nephrogenic mesoderm c The pelvis is the innermost portion and is in direct contact with the ureter 1 In reality the pelvis is an extension of the ureter which grew into contact with the caudal portion of the nephrogenic mesoderm 2 The pelvis serves to drain the numerous collecting ducts of the renal medulla a The pelvis is divided into subunits 1 Each pyramid is drained by one Minor Calyx a The number of minor calyces equals the number of renal pyramids 2 Several minor calyces will be drained by a Ma39or Calyx a The major calyces will drain into the ureter at a depression on the medial surface of the kidney called the M 1 The renal vasculature will also enter and exit the metanephric kidney at the hilus 2 The structure of the nephron is that of a long convoluted tubule beginning and ending in the renal cortex a It begins with Bowman s capsule which filters the blood of the glomerular capillaries in the cortex b The glomerular filtrate will next travel into the Proximal Convoluted Tubule where most of the modification of urine will occur c The early stage urine will next travel into the Proximal Straight Tubule which will dive into the medulla and forms the Descending m of the Loop of Henle d The urine will next travel into the Distal Straight Tubule which will rise through the medulla and back towards the cortex to form the Ascending Limb of the loop of Henle e The urine will finally pass into the Distal Convoluted Tubule which is located in the cortex 1The distal convoluted tubule empties into the collecting duct in the cortex 2 The reason that the distal convoluted tubule is located in the cortex is that it contains one component of the Juxtaglomerular Apparatus which serves to regulate renal blood pressure and thusly blood filtration a The other component is located in the afferent arteriole 2 External Salt Excretion a Vertebrates living in marine or arid environments can not afford to spare much body water to remove salts that have developed on external structures 1 Marine teleosts excrete salt through their gills 2 Elasmobranchs and coelacanths secrete salt by a Rectal Gland a The rectal gland stores accumulated salts and excretes this salt into the intestine near the cloaca for elimination 3 Certain reptiles have salt glands located near the orbit from which salt is excreted a These reptiles species include marine iguanas saltwater crocodiles marine turtles sea snakes and a variety of desert species 4 Sea birds have salt glands that are similar to those of reptiles 3 Urinary Bladders a Urinary bladders are a terrestrial adaptation designed to help conserve water 1 The urinary bladder will arise as an embryonic evagination of the ventral wall of the cloaca a In amphibians basal lizards turtles and monotremes mammals the bladder opens into the cloaca 1 The kidneys excretory ducts eg mesenephric ducts also open directly into the cloaca not the bladder a When the cloaca is closed urine will back up into the bladder which will serve to store and concentrate the urine prior to elimination b In placental and marsupial mammals the evagination of the cloaca that gives rise to the bladder is the allantois 1 The ureters drain into the urinary bladder of these mammals and the bladder is in turn drained by the Urethra a Since these animals lack the cloaca the urethra is necessary for the elimination of urine b There are structures in certain bony fishes that are sometimes referred to as urinary bladders 1 They are not homologous to the true terrestrial urinary bladder a When they exist they are basically terminal expansions or evaginations of the mesenephric tubules that empty into the cloaca b Their embryonic development is also different 1 Instead of arising from a cloacal evagination these bladders arise from the nephrogenic mesoderm B The Reproductive System 1 Gonadal Primordia a The gonads serve to produce gametes and sex hormones b The gonads arise as a pair of embryonic thickenings of the coelomic mesothelium medial to the mesenephric ducts called the Genital Ridge 1 Primordial germ cells will migrate into the genital ridge and become established there a These primordial germ cells are the progenitors of the sperm and egg cells b The region of the genital ridge that these cells become established in is termed the Germinal Epithelium c Initially the gonads have the potential to develop into either testes or ovaries 1 Genetics hormones and other factors will determine which gender will occur 2 Development a As the gonads develop they will enlargen and acquire a portion of the dorsal mesentery 1 The fold of dorsal mesentery associated with the developing testes is called the Mesorchium 2 The fold of dorsal mesentery associated with the developing ovaries is called the Mesovarium b In the gonadal primordial that will become the testes Primary Sex Cords form and invade deeper into the genital ridge 1 These primary sex cords will become the Seminiferous Tubules a Seminiferous tubules are lined by germinal epithelium and will serve as the site of sperm cell production c In the gonadal primordial that will give rise to the ovaries primary sex cords will also form however they are not gametogenic 1 Instead another set of cords called Secondary Sex Cords will form a Secondary sex cords are lined by germinal epithelium so they produce the ova b The secondary sex cords do not penetrate deeply into the genital ridge instead staying close to the surface 1 As a result the ova arise from the outer layer if the ovarian parenchyma the cortex 2 The primary sex cords will become reduced as they migrate deeper into the genital ridge to become a portion of the ovarian medulla d The release of the gametes will differ between the testes and ovaries 1 Eggs are released into the coelom or a compartment before being swept into the oviducts 2 Sperm will be conducted through an enclosed system of ducts that will convey them from the seminiferous tubules within the testes to the external environment a The only exception to this pattern is found in agnathans 2 The Testes and Male Duct System a The testes are fairly consistent in all vertebrates 1Germinal epithelium lines the seminiferous tubules a The germinal epithelium includes Spermatogonia the stem cells which will give rise to the Spermatozoa b The spermatozoa will drop into the lumen of the seminiferous tubules and into the duct system 2 Within the connective tissue between the seminiferous tubules are the Interstitial Cells of Leydig a Leydig cells produce the male sex hormones 3 Most vertebrates have internal testes Mammals are the exception having external testes a In some mammalian species the testes reside in the scrotum permanently and in some species temporarily 1 The passageway between the scrotum and pelvic cavity is the lnguinal Canal b The duct system serves to carry sperm from the testes to the exterior 1 The Pathway of Sperm in the Duct System a The beginning differs between mammals and other vertebrates 1 In mammals initially sperm travels from the seminiferous tubules to a network of vessels in the testes called the Rete Testis a From the rete testis the sperm will then travel into the epididymis 1The mammalian epididymis has two portions The first to receive the sperm are several highly convoluted ducts called the Efferent Ductules or Vasa Efferentia a These efferent ductules are actually mesenephric ducts which invaded the testes during development instead of the kidneys 2 Most other vertebrates have sperm traveling from the seminiferous tubules directly into the vasa efferentia b From the vasa efferentia in all vertebrates sperm will next pass into the Spermatic Duct 1 The spermatic duct is found in all vertebrates but its nature will vary a In mammals it is composed of the ductus epididymis vas deferens and urethra 1Sperm will pass from the efferent ductules into the singular Ductus Epididymis which makes up the bulk of the epididymis 2 It will then pass into the Vas Deferens a muscular tube that carries sperm from the scrotum into the pelvic cavity behind the bladder 3 Sperm will then enter into the Urethra a single tube that serves for the passage of sperm and urine a In therian mammals the urethra is long and well developed since they lack a cloaca There are three portions named for the structure that they pass through 1 Prostatic Urethra passes through the prostate and first receives the sperm 2 Membranous Urethra passes through the floor of the pelvis sometimes called the urogenital membrane 3 SpongyPenile Urethra passes through the penis It is the last portion to carry the sperm b In most vertebrate possessing a mesenephric kidney the mesenephric ducts serve as the sperm duct and will carry both sperm and urine 1The mesenephric duct will receive sperm from the vasa efferentia 2 Some variations a Some vertebrates lack seminiferous tubules 1 These are the hagfish lampreys certain jawed fishes and some urodeles 2 Instead their germinal epithelium may be either on the surface of the testis or deep within the testis a Their primordial germ cells form Seminiferous Ampullae cyst like structures that are built up and broken down based on breeding season b Some fish and urodeles have developed a new duct to carry sperm and so replace the mesenephric duct 1 This duct is called the Marginal Canal 2 This has resulted in teleosts as the mesenephric duct never carries sperm a In all other fishes and amphibians and in reptiles birds and mammals the mesenephric duct will remain in males throughout their lives and will serve to carry sperm 1 ln amniotes the mesenephric kidney does not utilize the mesenephric duct to carry urine so the mesenephric duct will carry only sperm a In amniotes the mesenephric duct is known as the VasDuctus Deferens c A number of multicellular glands will be associated with the male duct system 1 These glands produce a variety of secretions that together form Seminal M in amniotes a Seminal fluid aids the spermatozoa in a number of ways 2 These glands are called Accessory Sex Glands a They reach their greatest number and diversity in mammals 1 They include Ampullary Glands Seminal Vesicles Prostate Coagulating Glands and Bulbourethral Glands a Seminal vesicles in mammals serve only a glandular role but in other vertebrates that have them they also store sperm b Coagulating glands cause the ejaculate to coagulate in the female reproductive tract forming a plug to prevent other males from inseminating the female 3 lntromittent Organs a lntromittent organs are found inmost species that utilize internal fertilization 1 They are found in some fishes one frog family reptiles some birds and all mammals 2 Species that use internal fertilization but lack an intromittent organ will instead evert the cloaca to introduce sperm into the female reproductive tract a These species include most birds and some urodeles b Types of lntromittent Organs 1 Elasmobranchs have Claspers as intromittent organs a Claspers are modifications of the male pelvic fins 2 Some teleosts use a Gonadopodium a The gonadopodium is a modification of the first ray of the anal fin 3 Frogs of the Family Ascaphus have a permanent tubular structure extending from the cloaca 4 Snakes and lizards have Hemipenes a Hemipenes are a pair of protrusible diverticuli having a groove called the Spiral Groove for the transport of sperm b The hemipenes are stored internally until needed 5 Turtles crocodilians some birds and monotremes mammals have an erectile structure called a Penis a This penis is a thickening of the floor of the cloaca 1 This thickening is composed of well a vascularized connective tissue called the Corpus Spongiosum 2 It will contain a urethral groove for the transport of sperm a The urethral groove is on the dorsal aspect of the penis 3 It also has a distal thickening called the Glans Penis 6 Therian mammals have an erectile structure called a Penis but it differs from the previously mentioned penis of monotremes certain birds and certain reptiles a For one thing this penis does not arise from the cloacal floor but instead from a genital tubercle b Structurally it differs as well 1 It is composed of three tissue masses All three are cylindrical well vascularized connective tissue masses a There are a pair of dorsolaterally arranged tissue masses called the Corpora Cavernosa b There is a singular midventral mass called the Corpus Spongiosum 1The corpus spongiosum contains the urethra 2 The penile or spongy urethra unlike the urethral groove is an enclosed tube a It will carry both urine and sperm 3 The therian penis will also have an expanded distal portion called the glans penis a The glans penis is covered by a fold of skin called the Prepuce b The Clitoirs of therian females is homologous to the glans penis 4 The Ovaries a Ovaries vary quite a bit between the various vertebrates 1 ln anurans and urodeles ovaries are simply folded sacs 2 ln reptiles birds and monotremes the ovaries are filled with numerous fluid containing sacs called Lacunae 3 Many teleosts have large ovaries with a hollow center 4 A compact ovary is found in many other fishes including sharks and therian mammals b The hollow ovary present in many teleosts is lined internally by germinal epithelium 1 This germinal epithelium lines the lumencavity in the center a This lumen is actually a portion of the coelom that became trapped within the developing ovary b In oviparous species eggs are dropped into the lumen c In viviparous species young will be dropped into the lumen 2 Depending on the species the lumen of the ovary is either directly continuous with an Oviduct or partially surrounded by peritoneal folds called the Oviducal Funnel that will conduct the eggsyoung to the oviduct c The ovaries of marsupial and placental mammals are of the compact variety 1 Their ovaries have an outer covering of a simple cuboidal epithelium called Germinal Epithelium covering a tough layer of fibrous ct called the Tunica Albuginea 2 The parenchyma of the ovary is broken up into a cortex and a medulla a The medulla is the innermost zone and is composed of a well vascularized loose ct b The cortex is the outer zone and also is composed of a loose ct However this layer contains the Follicles 1 Follicles are cellular structures composed of one immature ovum surrounded by epithelial cells 2 Mammals typically produce only a few ova per ovulation a The follicular stage that ovulates is called the Graafian Follicle 1The ovum and a few surrounding epithelial cells are released during ovulation into the coelom a Ciliary beating will draw the ovum into the oviduct 2 The cells of the Graafian follicle that remain in the ovary after ovulation for the Corpus Luteum and endocrine structure 5 Female Genital Tracts a The female genital tracts in nontherian vertebrates are all fairly similar 1 They consist of a pair of muscular and glandular oviducts that begin at an opening to the coelom called the Ostium a The ostium is associated with an oviducal funnel b The oviduct will terminate in the cloaca or a subdivision of the cloaca 2 Ray finned fishes differ from all other nontherian vertebrates in the development of their female duct systems a Their oviducts are not homologous to the oviducts of other vertebrates being of a different embryonic origin b The oviduct is simply an extension of the ovarian lumencavity c The oviduct will open into a paired or unpaired External Genital Papillae 1 In some teleosts with unpaired external genital papillae the papilla will elongate to form an egg laying structure called an Ovipositor 3 ln vertebrates other than the ray finned fishes the female duct system develops from a pair of embryonic ducts called Muellerian Ducts a Muellerian ducts form during development in both genders however they degenerate in males b Muellerian ducts in elasmobranchs will give rise to an oviduct that will develop a Shell Gland and a Uterus 1 A shell gland secretes shell material and often albumin around the ovulated egg c Amphibian oviducts have numerous glandular evaginations along their lengths 1 These glandular evaginations will secrete jelly around the eggs d In female crocodilians and in most female birds only one Muellerian duct will develop The other will regress e In reptiles birds and monotremes the oviducts will possess shell glands b As in other vertebrates Muellerian ducts will give rise to the female duct system in therian mammalian However in therians the caudal extremities of the two Muellerian ducts unite They give rise to oviducts uterus and vagina 1 Oviducts are short tubules that serve to convey the egg from the ovary to the uterus a They have three segments 1 The first to receive the egg is the lnfundibulum which will be a funnelshaped structure lined with cilia a The opening of the infundibulum has fingerlie folds called Fimbriae which help to capture the ovum 2 The middle and longest segment is the Ampulla 3 The third segment is the Isthmus which connects to the uterus b The inner lining of the oviduct is a tunica mucosa having two types of epithelial cells ciliated columnar and secretory cells 2 m serve as the site of development 0 for the embryo and fetus prior to birthing a In marsupials the Muellerian ducts join only at the urogenital sinus 1 As a result marsupials have what is termed a Duplex Uterus a This means that there are two completely separated uteri right and left b the two uteri connect to two separate vagina b In placental mammals there is only one uterus and one vagina 1 The extent of fusion between the Muellerian ducts will vary between species resulting in two types of uteri a The most common is the Bicornuate Uterus where the uterus has two cornua horns connecting to a uterine body ex canines pigs b the other type is the Simplex Uterus which lacks cornua ex humans c The uterus will narrow closer to the vagina This region is called the Cervix d The uterine wall has three tunics 1 The outer tunic is the Perimetrium a serosa 2 The middle tunic is the thickest and a muscular layer called the Myometrium 3 The innermost layer is the highly variable Endometrium a The endometrium has two layers 1Stratum Basalis the permanent layer that lies against the myometrium 2 Stratum Functionalis is a highly variable mucosa that increases and decreases in thickness due to reproductive state 3 The Vagina is a hollow muscular tube running from the uterus to the urogenital vestibule or urogenital sinus Chapter 9 Terms Neurocranium braincase arises via endochondral ossi cation Splanchnocranium visceral skeleton arises via endochondral ossi cation Dermatocranium made up of integumentary bone membrane bone bones that form above and along side the brain upper jawmarginal bones primary palate opercular Parachordal cartilage that starts the braincase beneath midbrain and hindbrain Prechordal cartilage that starts the braincase anterior to notochord beneath forebrain Basal Plate parachordal notochord cartilage Ethmoid Plate prechordal cartilages united Olfactory Capsule nasal used for smell lots of formina for blood vessels Otic Capsule surrounds the otocyst inner ear lots of formina for blood vessels Optic Capsule forms the sclerotic coat of eyeball covers the eye Hypophyseal fenestra midline between ethmoid and basal plate Tectum cartilaginous roof above brain Chondocranium adult cartilage braincase Neurocranial Ossification centers where brain starts developing 4 places occipital sphenoid ethmoid and otic Basioccipital Bone underlying hindbrain ventral to foramen magnum Exoccipital Bones 2 of them lateral to foramen magnum Supraoccipital Bone above the foramen magnum Occipital Condyles articulate with the vertebra to help move the skull Basisphenoid midbrain and pituitary gland anterior to the basioccipital Presphenoid anterior to the basisphenoid Alisphenoid lateral walls Ethmoid region anterior to the sphenoid includes the ethmoid plateampolfactory capsulses Petrosal b0ne all of the otic centers fused together bird mammals Roo ng bones protective shield over the brain amp special sense organs forms the ring around the orbit Upper Jaw dermal bones tooth bearings maXillae Primary Palatal 7 roof of the oral cavity in tetrapods pterygoidsvomerspalatines Operculari ar of tissue that arises from hyoid arch Platybasic attened skull Columella amphibians middle ear Temporal Fossa cavernous opening in the temporal region in amniotes Temporal bone fused petrotympanic tympanic petrous and squamosal Anapsid lack temporal arches reptiles turtles Synapsida l lateral temporal fossa postorbital squamosal zygomatic archmammal Diapsid 1 pair of temporal fossae crocodilians Cranial kinesis movement of 1 section independent of the others snakes lizards Euryapsid l temporal fossa on dorsal dinosaurs due to convergence extinct 2ndary palate divides oral and nasal cavity mammals Palatal processes where the palatine maXillae and pterygoid meet crocodilians Palatal fissure found in incomplete 2ndary palates channels air in roof of oral cavity Palatal folds borders of the fissure Fontanels soft spots in incomplete skull allows for molding Inca bone post pariatal Periotic mammals fused prooticophisthotic epiotic ossi ed Otic capsule which is the mastoid process Styloid process hyoid arch temporal bone Cranial sinuses air lled areas in maXillafrontalsphenoidethmoid Pterygoid small winglike process of the sphenoid serve to attach jaw muscle Turbinal bones found in nasal mammals have 3 Visceral Skeleton Visceral Skeleton splanchnocranium includes all pharynegeal archs basihyal and basibranchial cartilages in sharks Mandibular arch platoquadrate top jaw and meckels cartilage bottom jaw Labial cartilage in between top and bottom jaw unknown function Hyostylic jaw suspensionhylostyly top jaw braced against hyomandibula new sharks Amphistyly jaw independently braced against neurocranium older sharks Autostyly jaw is attached to neurocranium oldest sharks chimera Quadrate ossi ed platoquadrate bony sh Articular bones ossi ed meckel s cartilage Incus the quadrate bone in mammals middle ear Malleus articular bone in mammals Entoglossus hyoid that extends into the tongue works with the comua Lore space between the eyes and the bill Tympanohyal connects the tympanic bulla and the hyoid aka cranial horns Notes Neurocranium arises as cartilage then ossifys in cartilaginous sh Gnathostomes neurocranium in several pieces then expands to form 1 braincase Neurocranium starts out as parachordal amp prechordal cartilage which Olfactory amp Otic Capsule both arise as cartilage and need access to airwater Optic Capsule not part of neurocranium Foramen magnum largest hole rear of brain All starting cartilage is from mesenchyme the rest is from the neural crest The 4 Occipital Bones supraexo2basi fuse in mammals occipital bone Reptiles Sphenoid ossify independently Mammals the sphenoid bone may ossify to include all basisprealisphenoid Most tetrapods develop no ethmoid ossi cation centers Anmiotes mesethmoid bones for the ethmoid region Anurans sphenethmoid is the only ethmoidsphenoid bone Tetrapods have formed a 2ndary palate to separate the nasal and oral cavities Mammals only dentary as lower jaw Angular bears no teeth Hypobranchial plate allowed to walk on land and breath Ear ossicle evolved from a part ofthe jaw Cricoid amp arytenoids evolved from the Sth pharyngeal arch Thyroid cartilage arise from the 43911 arch Ossi cation centers of the neurocranium are occipital sphenoid ethmoid and otic In all gnathostomes the articular and quadrate bones make up the jaw except in mammals they become the middle ear ossicles malleus incus Chapter 7 Terms Hydroxyapatite Crystals turns collagen to bone calcium phosphate ions Cementing substance hold the crystals in the matrix is water mucosugars Osteoblast form bone Chondroblast Immature cartilage cell Chondrogenesis forming cartilage Odontoblast form dentin Ameloblast form enamel Fibroblast form collagen Myoblast form muscle Scleroblast can be made into osteochondroodonto or ameloblast Mesenchyme stem cells can turn into fibromyoscleroblast Chondrocytes chondroblasts that are trapped in lacunae Collagen made up of rils create collagen bundles Lacunae house osteocytes in interstitial uid Canaliculi canals that connects the lacunae Compact Bone layers of collagen around a haversian canal Haversian Canals vascularize the collagen bundles in compact bone can branch and rebranch Osteoanaversian System Haversian canal and the sourrounding lamellae Periosleal Bone outer bone formed by osteoblasts on the inner surface of the periosteum Periosteum dense fibrous membrane that covers all bones at the articular surface ends Spongyl Cancellous Bone bony trabeculae and bone marrow found in the epiphysis Trabeculae protects against stress inside the bone in the diaphysis Marrow occupies the cavities bt trabeculae reticulum of connective tissue fibers Can be red produces red blood cells or yellow tissue adipose Endosteum lines the marrow cavities Dentin odontoblasts not trapped to lacunae forms on outer layer of dermis coated by enameloid Osteogenesis forming bone Dentinal Tubules canaliculi like process in dentin Acellular bone Aspidin no cells no canals Blastema any aggregation of mesenchyme that with a stimulus forms some tissue Membrane Bone no cartilage bone formation can be compact or spongy Dermal Bone bone in the dermis Replacement Bone bone deposited where hyaline cartilage exists Endochondral Ossification cartilage to bone Intramembranous Ossification bone formation wo cartilage precursor membrane bone Epiphyseal Plate narrow cartilage found on long bones growth plate bt diaphysis and both epiphysis occurs wage Appositional growth cartilage growth from perichondrium Intersitial growth cartilage growth from within the matrix Perichondrium bounding membrane created by mesenchyme surrounds cartilage organs with connective tissue sheath 2 layered 15t tough berous 2nd chondroblasts mesenchyme Hyaline Cartilage precursor of replacement bone Fibrocartilage thick dense collagenous bundles intervertebral discs Elastic Cartilage network of elastic fibers Calcified Cartilage Calcium deposited in matrix of hyalinefibrocartilage mistaken for bone jaws of sharks Tendons connect muscle to bones resists tension of muscle contraction Ligaments connect bone to bone Aponeuroses wide and flat tendonsligaments gala aponeurotica mammal scalp Nuchal Ligament longest ligament in mammals Sesamoid CartilageBone mineralized nodules in tendonsligaments patella Arthrosis joint site where two bonescartilage meet Diarthrosis free moving joint articular surface hyaline cartilage Amphiarthrosis limited moving joint fibrocartilage Synarthrosis Immovable joint Sutured joint Ankylosis suture disappers between two bones Symphysis joint in the middle of the body where two bones are connected by a pad of fibrocartilage Heterotopic bones develop in areas of continuous stress os penis os clitoridis Notes Dentin 9 placoid scales by odontoblasts found in ray nned scales amp elasmobranch fishes and in teeth Aspidin Bone found in flexible scales of fish and is the matrix of vertebrate teeth Membrane boneReplacement Bone blastema must develop then bone can form or be replaced Periosteal Bone Membrane bone Ecotherms never ending chondrogenesis ofepiphyseal plate BirdsMammals epiphyseal plate 9endochondral Ossification occurs to create epiphyseal line Cartilage can diffuse therefore no blood vessels are needed in the matrix Cartilage Formation chondroblasts deposite cementing substance then the perichondrium Skeletal Remodeling occurs all the time in order to maintain homeostasis addsremoves calcium from bones based on calcium levels in blood allows bones to expand not thicken Thicker bones more stress Haversian Systems amniotes Osteon Bone is the deepest hardest layer of compact bone where haversian canals are found LigamentsTendons can be calcified Chapter 10 Terms Interclavicle found in early tetrapods used to brace girdle not found in sh Clavicle associated with coracoid both used to brace the scapula against sternum Furculum clavicle wishbone found in birds Coracoid Plate forms the coracoids in tetrapods anteriorprocoracoids posteriorcoracoids Scapula present in all tetrapods allows for articulation of pectoral girdle Acromion process allows for muscle attachment on scapula Mammalian clavicle used to brace against the scapula lost in some species Ischiopubic plate pelvic girdle fish Pubis tetrapod s pubic bone Acetabulum where head of femur goes Pelvis sacrum and pelvic girdle fuse amniotes Epipubic marsupial bonepouch reptiles Innominate Bone coxal bone hip bone made up of the pelvis illium ishcium Sacroiliac joint fusion of the ilium and sacrum Relaxin hormone that relaxes during pregnancy Lepidotrichia bony fish rays Ceratotrichia cartilaginous fish rays Paired fins 3 groups lobed sarcopterygians find fold chonrichthyans ray fins actinopterygians Lobed Fins biserial or two series of radial cartilage Fins folds board base have clasper Ray Fins teleosts more exible no pelvic fins Anal frn behind the anus Gonopodium modified anal fin used for mating analogous to the clasper median fin Heterocercal caudal fin notochord turns upward into dorsal lobe modern sharks Hypocercal rare vertebral column turns downward ventral lobe longer than dorsal lobe Diphycercal dervived from heterocercal fins vertebral column ends wno upbending Hemocercal notochord enchased in urostyle turns dorsally 139 39 139 139 r r r r Tetrapod Limbs 3 eoment 39 r Manus hand Propodium upper arm humerus Epipodium forearm ulna radius Autopodium wrist palm digits Tibiofrbula fibula and tibia united found in reptiles Tibiotarsus birds tibia fuses with the proximal rox of tarsals Pentadactyl five digit limb Radiale proximal row in digit articulates w radius Ulnare ulnar carpal articulates w ulna called cuneiform Pisiform sesamoid bone found in reptiles and mammals end of the wrist Centralia middle row of carpals Distal carpals distal row of the carpus Phalanges digits Hamate bone fusion of distal carpals 4 5 PolleX thumb Carpometacarpus 3 distal carpals united with three metacarpals birds Alula lst nger on birds independently movable Running Plantigrade mammals everything rests on the ground when at Digitigrade only the digits rest on the ground Unguligrade fastest only the hoofs touch the ground Artiodactyls paraxonic even number of digits Mesaxonic odd number of digits Opposable thumb one that can be made to touch the tips of each other digit PrehalluX evolved into tarsal or metatarsal has been lost Foot Astragalocalcaneus single bone that articulates with bula and tibia lizards Tibiotarsus proximal tarsals fused with tibia birds Tarsometatarsus distal tarsals are united with the upper end of three fused metatarsals HalluX great toe primates Metatarsal arch instep hominoids foot arch Centrale between with tibiale and proximal rox of the tarsals Locomotion Serpentine mode used for snakes Rectilinear Locomotion conveyor belt Notes Urodeles and apodans no clavicles Pelvic Gridle No dermal bones Patella birds mammals ossifies in the tendon Chapter 6 terms Keratin Flattens cells squamous and kills them Prevents Dehydration Conjunctiva Skin covering the eye Cornified Kerantinized Goblet Cellgland Unicellular secrete mucus Granular cellgland Secrete mucus pheromones sh amphibians Photophore Light emitting cells of deep sea sh Alveoli Cup shape sacs Tubular long tube glands found in humans Merocrine Gland most common sweat gland in humans secretes product to cell membrane Holocrine Gland Oil glands secrete themselves Apocrine Gland Cell pinches off its product Mammary Glands Mucous Gland Secrete Mucus unicellular Femoral Glands Lizard Granular Gland Parotoid Gland toad granular gland Uropygial Gland Bird Oil Gland Sebaceous Gland alveolar secrete oilsebum for hair lubricates vaginapenis Ceruminous Gland ear oil gland secrete cerumen earwaX Meibomian Gland moistens eye Chalazion in amed hair duct Sudoriferous Gland sweat glands tubular mammals Mammary Glands alveolar gland form on milk lines sebaceous gland Scales repetitious stratum corneum amniotes only Scutes scales used for movement snakes Unguis hard top of nail Subunguis soft bottom nail Cuneus comified pad ungulates softer then subunguis Arrector pili muscle that controls hair smooth muscle Arrector Plumarum muscle that controls feathers smooth muscle Pterylae feather track Dermal Papilla grows from epidermis to dermis vascularizes hair follicles Vibrissa whiskers used for touch Bovine Horns true horns artiodactyls don t shed nonbranched dermal bone Pronghorn True horn branched shed yearly dermal bone Hair Horns keratinized hair fibers solid bone on nasal area rhinos AntlersGiraffe Horns fake horns frontal bone covered in velvet Baleen whale tooth used for straining Ischial callosities thick pads on monkeys Tori epidermal pads used for walking Apical Pads tori found on distal digit CornsCalluses caused by friction thickenings of stratum corneum Dermis 2 layered can become ossified Dermal Bone 4 layered lamellar spongy dentin enamel Denticles spiny elevations of dentin Lamellar compact layered bone Spongy Bone vacularized softer Rhomboid 4 layered dermal scale evolved to ganoid and cosmoid Ganoid evolved to elasmoid found in gars no spongy bone Cosmoid no living species Elasmoid only laminar bone found in bony fish 2 subtypes cycloidampctenoid Cycloid free border elasmoid scales exible Ctenoid hair border elasmoid scales exible Placoid sharksrays has a spine of enameloid coming from basal plate denticle Osteoderms bone in dermal layer in land animals tetrapods crocodiles Chromatophores contain pigment granules can disperse causes physical color change Melanophores brown pigment chromatophores causes hair color Melanosomes houses melanophores Xanthophores yellow granules Erythrophoresred granules Lipophores XanthophoresErythrophores lipid soluable Iridophores re ectdisperse light cause silver Blue feathers actually brown Morphologic color change tanning Melanocytes pigment cells not in skin permenantly dispersed Super cial fascia mammals loose connective tissue of adipose separates hypodermis and muscle Chapter 6 important Facts Craniates non vascular epidermis vascular dermis Fish epidermis produces mucus Hairs arise from follicles made up of bulb dermal papilla root where cell cornif1cation happens and shaft surrounded by sebum Hairs spine quills etc Dermis collagenous connective tissue houses chromatophores hair follicles erector muscles and multicelluar glands Unicelluar glands most fishes Multicelluar glands most amphibians onward 3 types of feathers contour give bird shape downfeathers uffy feathers found in young birds and loplumes tip of feathers that have nerve endings Scales evolved 9 hairfeathers Mammals 3 layer epidermis stratum germinativum basal or bottom layer highly regenerative stratum granulosum middle layer and stratum corneum top layer Integument 9 functions protection main role exteroreceptive respiration excretion thermoregulation locomotion homeostasis nourishment Pg123 PgllOlll Chapter 16 The Nervous System A Introduction 1 The nervous system has three interrelated functions a Sensory Input using millions of sensory receptors to monitor stimuli in both the external and internal environments b Integration the processing and interpretation of the sensory input c Motor Output the activation of effector organs to respond to stimuli 1 The effector organs include our muscles and glands 2 The nervous system can be initially broken up into two major divisions which can be further subdivided a Central Nervous System CNS 1 The CNS consists of the brain and spinal cord a It is located in the cranium and the vertebral canal 2 The CNS is the integrating and command center of the body a It interprets the sensory input integrates it and determines a motor response b Peripheral Nervous System PNS 1 The PNS carries information to and from the CNS 2 The PNS can be divided into a The Sensory or Afferent Division carries sensory information to the CNS from the sense receptors It can be further divided 1 Somatic Sensory sensory innervation of the outer portions of the soma the body It can be subdivided into a General Somatic Senses senses whose receptors are spread widely throughout the outer body 1 It receives information about pain temperature pressure touch vibration and proprioception the amount of stretch on muscles joints and tendons b Special Somatic Senses senses whose receptors are concentrated in a small specialized area 1They are the senses of vision olfaction audition and equilibrium 2 Visceral Sensory sensory innervation of the inner body the viscera the heart lungs Gl tract etc It can be subdivided a General Visceral Senses senses whose receptors are widely distributed throughout inner body the viscera 1 It receives information about pain temperature stretch nausea irritation hunger amp chemical changes b Special Visceral Senses senses whose receptors are concentrated in a small specialized area 1There is only one sense considered in this category taste b The Motor or Efferent Division carries motor information from the CNS from the sense receptors It can be further divided 1 Somatic Motor motor innervation of most of the skeletal muscles excepting the pharyngeal arch muscles It is also known as the Voluntary Nervous System It can not be subdivided 2 Visceral Motor motor innervation of the inner body the viscera It can be subdivided a General Visceral Motor controls the cardiac and smooth muscles It is also known as the Autonomic Nervous System ANS or Involuntary Nervous System b Special Visceral Motor it controls the pharyngeal arch musculature a special group of skeletal muscles 3 Nervous Tissue a Nervous Tissue the main component of the nervous system has a high cellular content 1 Over 80 of the tissue mass is cellular 2 There are two classes of cells in nervous tissue a Neurons the cells which send the nerve impulses b Neuroglia the supporting cells of the nervous system 4 Neurons a Neurons are the nerve cells proper 1 They are highly specialized cells that conduct the nerve impulse 2 Other characteristics of neurons include a nondividing all neurons are produced prior to birth and are not replaced b long living since they can not be replaced neurons must last us for our entire lifetimes Note there may be a possible exception in the cerebral cortex c very high metabolic rate neuronal metabolism is very high so these cells require much glucose and oxygen b The Neuron and Its Anatomy 1 The Cell Body aka39 nucleosome perikaryon a uninucleated b It contains the typical organelles of human cells as well as 1 m or Chromatophilic Bodies large clusters of BER and free ribosomes a Nissl bodies serve to produce proteins to replace those lost from the nucleoplasm and to repair the nucleolemma 2 Neurofibrils or Neurofilaments bundles of intermediate filaments running between the Nissl bodies a They serve to resist stress on the neuron c Most perikarya are located in the CNS where they can be protected by the vertebrae and skull 1 Those perikarya located outside of the CNS in the PNS are grouped together and surrounded by ct forming Ganglia 2 Dendrites a Dendrites are one of the two classes of processes radiating out from the perikaryon b Dendrites typically serve as receptive sites receiving the impulse and conducting it toward its perikaryon c Typically dendrites are more numerous and show a greater degree of branching than does the second class d Dendrites contain most of the organelles found in the cell body including extensions of the Nissl bodies 3 Axons a Axons are the second class of cellular processes radiating out from the perikaryon b Typically axons serve as impulse distributors sending the impulse from the perikaryon out to another cell c Each neuron generally has only one axon 1 The axon arises from a swollen region on the cell body called the Axon Hillock d Along with the other cytoplasmic organelles the axon has a high component of neurofibrils microtubules and actin filaments 1 These cytoskeletal components add support to the axon which can be of great length and also aid in the transport of substances through axonal transport e Axons branch to a much much lesser extent than do dendrites but they may have some branches present 1 Axon Collaterals rare branches which branch off at 900 angles to the axon 2 Telodendria many branches occurring at the terminal end of the axon 3 Axon Terminals aka end bulbs axonal boutons these are knoblike endings of the telodendria a These axon terminals synapse with the dendrites of other neurons usually 1 As a result the contain Neurotransmitters f To improve on the conduction of the impulse the axon will often be ensheathed in an insulating material called Myelin 1 Myelin is produced by a supporting cell called the Schwann Cell a Myelin is actually the cell membrane of the Schwann cell b This sheath of Schwann cells along the length of an axon forms what is called the Neurilemma 2 An axon and its myelin sheath is called a Nerve Fiber a Nerve fibers travel in groups for improved durability 1 In the CNS these groups are called Fiber Tracts 2 In the PNS these groups are called Nerves a Nerves are wrapped in fibrous sheaths 1 Epineurium ensheathes the entire nerve organ a It is the outermost sheath 2 Perineurium ensheathes a nerve fascicle 3 Endoneurium ensheathes a single nerve fiber a It is the innermost sheath c Neurons can be classified in two ways structurally and functionally 1 The Structural Classification of Neurons is based on the number of processes radiating out from the neuron cell body a Multipolar Neurons these are neurons having three or more radiating processes 1 Usually only one of the processes is an axon and the rest are dendrites 2 By far the most common type of neuron accounting for about 99 of all neurons b Bipolar Neurons these are neurons having two radiating processes one axon and one dendrite 1 These are rare neurons being found in association only with some of the special senses c Unipolar Neurons these are neurons having only one radiating process that serves as both an axon and a dendrite 1 These are also rare neurons making up the typical sensory nerves 2 Sometimes the unipolar neuron is also known as the Pseudounipolar Neuron a They may actually originate from bipolar neurons whose processes fused during development 2 The Functional Classification of Neurons is based on the direction of information flow relative to the CNS a Sensory Neurons aka39 Afferent Neurons send the impulse towards the CNS from sensory receptors of the PNS 1 Most afferent neurons are unipolar with their perikarya located in ganglia in the PNS a The central process of their single process serves as an axon and carries the information towards the CNS b The peripheral process of their single process serves as a dendrite and extends to the receptors to pick up the impulse b Motor Neurons aka39 Efferent Neurons carry the impulse a way from the CNS out to the effector organ 1 Most motor neurons are multipolar and have their cell bodies located in the CNS c lnterneurons aka39 Association Neurons lie between the sensory and motor neurons 1 Located only in the CNS 2 Most interneurons are motor neurons d Neurons communicate with one another and with other cells at a point called a Synapse 1 Synapses can be electrical or chemical a In a chemical synapse chemicals called Neurotransmitters are used to carry the message across a gap called the Synaptic Cleft 3 Supporting Cells or Neuroglia a The neuroglia are able to reproduce throughout our lifetimes b The neuroglia of the CNS are often called Glial Cells 1 Astrocytes a Astrocytes are the most abundant of the glia b They have many radiating processes which are attached to neurons and blood vessels 1 These processes give the cells their name 2 These processes may serve to transfer nutrients from blood vessels to neurons c Astrocytes may also 1 help to regulate the ionic balance of the environment around the neurons 2 recycle neurotransmitters 2 Microglia a These are the least abundant of the glial cells b They are also the smallest type of glial cell c Microglia are phagocytic cells that defend the CNS from foreign invaders and will also consume dead neurons 3 Ependymal Cells a These glial cells are actually a simple cuboidal ciliated epithelium b The ependymal cells form a lining in the hollow spaces of the brain and spinal cord 1 ex ventricles central canal 2 They allow for the circulation of cerebrospinal fluid throughput these hollow spaces and its diffusion into the tissues of the CNS 4 Oligodendrocytes a These cells have processes which wrap around and insulate CNS neurons 1 The insulating material is termed Myelin 2 The processes of one oligodendrocyte can insulate several CNS axons 3 Oligodendrocytes of the CNS have the same functional role as do the Schwann cells of the PNS c The Neuroglia of the PNS is made up of two fairly similar cell types 1 Satellite Cells a These cells surround and support the perikarya of PNS neurons within the ganglia 2 Schwann Cells a These neuroglial cells surround the axons of PNS neurons forming the PNS s myelin sheath 1 Myelin is a lipoprotein and is actually a modification of the Schwann cell membrane b Based on the interaction of the Schwann cells and the PNS neurons there are two classes of PNS axons recognized 1 Myelinated Axons these are quickly firing neurons 120ms due to the fact that the Schwann cell membranes are wrapped in thick layers about the axon insulating it 2 Unmyelinated Axons these are slow firing neurons 05ms because large segments of the axon lack a myelin coating and the myelin coating of these axons is much thinner Both decrease the amount of insulation afforded 4 Growth and Differentiation of the Nervous System a The Neural Tube 1 The neural tube develops from surface ectoderm by the process of Neuralation a The resultant neural tube is dorsal and hollow 1 The hollow center of the neural tube is called the Neurocoel b The cephalic portion of the neural tube will develop into the brain 1 The remainder of the neural tube will develop into the spinal cord 2 Shortly after the differentiation of the brain from the spinal cord the embryonic spinal cord will begin to display three zones a Marginal Zone is the outermost layer 1 It is relatively low in cell content b Ventricular ZoneGerminal Layer is innermost layer and is the layer lining the neurocoel 1 It is an area of highly mitotic cells c Intermediate ZoneMantle Layer is the middle layer and surrounds the vascular zone 1 This layer fills with cells produced by the ventricular zone a These cells will migrate into the intermediate zone from the ventricular zone and give rise to two lineages of cells 1The two lineages are a Neuroblasts that will develop into neurons b Neuroglial Stem cells which will develop into the neuroglia b As they grow and differentiate grey and white matter will become established 1Grey matter will form in the center of the developing spinal cord due to the proliferation of neurons and neuroglia in the intermediate zone 2 White matter forms in the marginal zone as axons from neurons in the intermediate zone migrate into the marginal zone c The cells of the ventricular zone will become the ependymal cells lining the central canal 3 In the embryonic spinal cord hindbrain and midbrain two plates of developing nervous tissue form one above and one below an invagination in the midpoint of the neurocoel a called the Sulcus Limitans a The plate above the sulcus limitans is called the Alar Plate 1 The neuron cell bodies that develop in the alar plates will develop into sensory neurons b The plate below the sulcus limitans is called the Basal Plate 1 The neuron cell bodies that develop in the basal plates will develop into motor neurons b The Development of Motor Neurons 1 The basal plate gives rise to motor neurons a Most of these motor neurons will be Somatic Motor neurons and will extend their axons from the CNS to the skeletal muscle organs 1 The perikarya of somatic motor neurons will remain within the CNS b Some of the motor neurons will be Visceral Motor neurons and will extend their axons into autonomic ganglia 1 The axons of these visceral motor neurons will synapse with the dendrites of other visceral motor neurons whose perikarya are located within the autonomic ganglia a These neurons are termed the Postganglionic Neurons of the ANS 2 The ANS neurons arising from the CNS are called Preganglionic Neurons c The Development of Sensory Nerves 1 Typically some of the sensory nerves will arise from Neural Ectoderm and some will arise from the alar plate a The neural crest ectoderm will be a paired structure flanking the developing neural tube 1 During development the neural crest ectoderm will break up into a metameric series one pair per body segment 2 Some of the neural crest cells will develop into sensory neurons of the CNS a During development these neurons will have a bipolar stage 1This bipolar stage may or may not be temporary 2 During the bipolar stage the developing neuron will send one process into the CNS and one process out to the sense receptors a The process sent into the CNS will be the axon b The process sent to the receptors is the dendrite c The cell bodies will become located outside of the CNS in a ganglion associated with the spinal cord called the Dorsal Root Ganglion b These sense neurons become what are termed First Order Neurons because they are the first to receive the impulse from receptor organs and to conduct it towards the CNS b Neuroblasts in the alar plate will also become sensory neurons 1 These sense organs will receive the sensory impulse from the first order neurons a As a result they are referred to as Second Order Neurons 2 There are 3 major exceptions to the general rule that the perikarya of first order neurons are located in sensory ganglia a The olfactory receptor cells are first order neurons whose cell bodies are located in the olfactory mucosa b The cells that give rise to the optic nerve called Ganglion Cells are first order neurons whose perikarya are located in the retina c Cell bodies of most proprioceptive branches of cranial nerves are located in the brain stem 1 The exception to this are the proprioceptive branches located in CN 11 and 12 B The Spinal Cord and the Spinal Nerves 1 The Spinal Cord a The spinal cord serves to connect the PNS and the brain 1 It is located in the vertebral canal 2 The spinal nerves allow for communication between the spinal cord and the rest of the body a Spinal nerves enter and exit the vertebral canal by way of the intervertebral foramina b Spinal nerves arise in a regular segmental pattern for most of the length of the spinal cord b The spinal cord and the brain are protected by an outer connective tissue sheath called the Meninges 1 In most fishes this protective ct sheath is a delicate ct membrane called the Menix Primitiva 2 In other nonmammalian vertebrates the meningeal sheath has two layers a The outer layer is a tough ct called the Dura Mater b The inner layer is a vascular membrane called the Leptomenix 3 Mammals have three meningeal layers a The outer layer is the toughest and is called the Dura Mater 1 The spinal and cranial dura maters differ slightly a The spinal dura is surrounded by a layer of adipose located between the spinal cord and walls of the vertebral arch b The adipose layer is lacking in the cranial dura mater Instead this dura mater has two layers the more superficial layer fuses in many places to the periosteum of the cranial bones c The spinal cord begin where it meets the medulla oblongata at the level of the foramen magnum 1 For most vertebrates the spinal cord terminates before the end of the vertebral column ex in humans the spinal cord ends at L2 or L3 a The end of the spinal cord is a tapering structure called the Conus Medullaris 1 Numerous spinal nerves will arise from the conus medullaris a They form what is termed the Cauda Eguina 1 Although they all arise at the same point these spinal nerves will radiate in a regular segmental pattern emerging at regular intervals as pairs exiting intervertebral foramina d The Arrangement of Gray Matter and White Matter in the Spinal Cord 1 Gray Matter a The gray matter is primarily composed of unmyelinated axons dendrites and perikarya b The gray matter is surrounded by white matter in the spinal cord and in turn encloses the central canal c Spinal cord gray matter has an H like shape 1 The Gray Commissure connects the two halves of gray matter a It is like the bar on an H b It has the central canal ie neurocoel inside it 2 There are a pair of posterior arms called the Posterior or Dorsal Horns a These horns are composed of interneurons receiving sensory information from the PNS 1These sensory neurons have their perikarya in the PNS in a ganglion called the Dorsal Root Ganglion b 80 the dorsal horns process sensory information 1This sensory information is divided into somatic and visceral sensory d There are a pair of anterior arms called the Anterior or Ventral Horns 1 These horns have the cell bodies of motor neurons whose axons are extending out towards the effector organs a 80 the ventral horns process motor information e In the thoracic and superior lumbar portions of the spinal cord the gray matter also has small Lateral Horns 1 As is the case for the ventral horns the lateral horns contain the cell bodies of motor neurons 2 White Matter a Spinal cord white matter is primarily composed of myelinated axons 1 These axons are carrying information between the brain and spinal cord and between different portions of the spinal cord There are three classes of axon tracts in the spinal cord a Ascending Tracts 1 Most carry sensory information from the receptors to the brain b Descending Tracts 1 Most carry motor information from the brain to the effector organs c Commissural Tracts 1These tracts carry information from one side of the spinal cord to the other 2 The Spinal Nerves a Spinal nerves allow for communication of sensory and motor information between the spinal cord and the body 1 They pass through the intervertebral foramina 2 Where the spinal nerve meets the spinal cord it is connected by two spinal nerve roots that serve to segregate information a Ventral Roots carry motor information from the spinal to the body 1 The ventral root is composed of the axons of somatic and visceral motor neurons b Dorsal Roots carry sensory information into the spinal cord from receptor organs 1 The dorsal root has a swollen structure called the Dorsal Root Ganglion which contains the perikarya of sensory neurons a Typically these are unipolar neurons 2 The dorsal root will consist of dendrite entering the dorsal root ganglion and axons running from the dorsal root ganglion into the spinal cord c The above described condition is the typical condition of most gnathostomes especially tetrapods and chondrichthyes 1 In the primitive condition however things were different a The two spinal roots never join distal to the spinal cord to form a single spinal nerve b The dorsal root contains visceral motor axons as well as sensory information c The dorsal root lacks a dorsal root ganglion d Initially the sensory neuron perikarya did not aggregate However when they did the neurons were bipolar not unipolar 2 The primitive condition is seen today in agnathans a In lampreys the dorsal and ventral roots do not join while in hagfish they unite but only in the trunk b the dorsal roots of agnathans possess visceral motor fibers c Some sensory cell bodies of agnathans are located in ganglia but most are not d Most sensory nerves in agnathans are bipolar neurons 3 ln fishes other than elasmobranchs the spinal nerves are much like those of other gnathostomes except that the dorsal roots will contain some visceral motor fibers b Occipitospinal Nerves 1 Occiptospinal nerves are found in many fishes and amphibians a They arise between the last pair of cranial nerves and the first pair of the more typical spinal nerves 2 Occipitospinal nerves generally lack the dorsal root of the typical spinal nerve 3 They innervate the hypobranchial musculature for the most part 4 Although amniotes lack occipitospinal nerves cranial nerves 11 and 12 may be derived from occipitospinal nerves a CN 11 and 12 lack dorsal roots as do occipitospinal nerves c Spinal Nerve Metamerism 1 ln gnathostomes a spinal nerve pair will arise at each body segment of the spinal cord except near the end of the tail d Spinal Nerve Rami and Plexuses 1 Almost immediately after the spinal nerve exits the intervertebral foramen it will give rise to two branches These two branches are the Dorsal and Ventral Rami 2 The dorsal ramus carries motor and sensory information to and from the dorsal body the epaxial muscles and dorsal integument 3 The ventral ramus is also both sensory and motor It will innervate the ventral body and also the lateral body wall a In the thoracic and lumbar regions it will also give rise to branches allowing for communication between the spinal nerve and sympathetic ganglia 1 these two branches are the White Ramus Communicans which carries information into the ganglion and the Grey Ramus Communicans which carries information out of the ganglion b The ventral rami will also give rise to the nerve plexuses that control the limbs 1 There are up to four plexuses depending on the vertebrate class Cervical Brachial Lumbar and Sacral although in some cases two plexuses be considered as one plexus ex Lumbosacral D The Brain and Cranial Nerves 1 The Brain a Introduction 1 During the embryonic period the cranial portion of the developing neural tube will begin to expand and then eventually form the brain a In all vertebrates the cranial expansion of the neural tube will give rise to 3 vesicles 1 Prosencephalon is the anteriormost vesicle and will give rise to the forebrain 2 Mesencephalon is the middle vesicle and will give rise to the midbrain 3 Rhombencephalon is the posteriormost vesicle and will give rise to the hindbrain b The three vesicles will further develop to produce the 5 principle regions of the brain 1 The prosencephalon will give rise to the Telencephalon aka Cerebrum and Diencephalon 2 The mesencephalon remains as a single vesicle which will be also referred to as the Midbrain 3 The rhombencephalon will give rise to the Metencephalon the cerebellum and pons and the Myencephalon the medulla oblongata c The differentiation of the three primary vesicles into the five regions of the brain is accomplished by a series of developmental events 1 One event is the localized thickening on the roor and lateral walls of some vesicles 2 Another event is the formation of dorsal lateral or ventral evaginations that will be either median or paired evaginations in some vesicles b The Ventricles of the Brain 1 Introduction a Ventricles are cavities within the brain b Ventricles are lined with ependymal cells and are filled with cerebrospinal fluid c There are four ventricles in the brain All are in continuous with one another and are in contact with the central canal of the spinal cord 2 The Four Ventricles a The Lateral Ventricles aka first and second ventricles 1 These are a pair of Cshaped ventricles located within the cerebral hemispheres of the telencephalon a Due to their shape they have three horns anterior horn posterior horn and inferior horn 2 The anterior portion of the lateral ventricles are quite close and are separated only by a thin median membrane called the Septum Pellucidum b The Third Ventricle 1 The third ventricle is located in the diencephalon 2 It is connected to the lateral ventricles by the two lnterventricular Foramen 3 The third ventricle narrows in diameter posteriorly in the mesencephalon forming the Cerebral Aqueduct which communicates with the fourth ventricle c The Fourth Ventricle 1 The fourth ventricle is located in the hind brain between the cerebellum and the brain stem 2 It connects inferiorly to the central canal of the spinal cord and medulla oblongata 3 The fourth ventricle has three apertures or openings which connect it to the subarachnoid space a The subarachnoid space is a fluid filled space surrounding the entire CNS bThey allow the CSF of the ventricles to enter the subarachnoid space c They are the two Lateral Aperatures and the Median Aperature c The Hindbrain The Myelencephalon and Metencephalon 1 The Myelencephalon is the Medulla Oblongata a The medulla oblongata is the caudalmost portion of the brain stem 1 It connects directly to the spinal cord at the foramen magnum b Anatomy and Functions 1 Pyramids a The pyramids are located along the ventral midline b It contains the pyramidal tract from the cortex 1The pyramidal tracts cross over in the medulla at the point known as the Decussation of the Pyramids 2 lnferior Cerebellar Peduncles a These are fiber tracts connecting the cerebellum to the medulla oblongata b They are located along the lateraldorsal portion of the medulla 3 Olives a The olives are located immediately lateral to the pyramids b Each olive contains a wavy structure of gray matter termed the inferior olivary nucleus 1 It serves as a relay station for sensory information traveling towards the cerebellum a Especially for proprioceptive information 4 The medulla also contains the nuclei for the five inferiormost pairs of cranial nerves 5 It also houses much of the Reticular Formation that exerts autonomic control of a Cardiac Center adjusts the force and rate of the heart beat b Vasomotor Center regulates blood pressure c Medullary Respiratory Centers regulates respiratory rate d It also has centers controlling other responses such as sneezing vomiting hiccupping swallowing and coughing e These functions are also controlled by the hypothalamus which sends information to the reticular formation 2 The Metencephalon is made up of the pons and cerebellum a The pons like the medulla is a portion of the brain stem 1 The pons is located between the midbrain and the medulla anterior to the cerebellum and fourth ventricle 2 The pons contains a The nuclei of some of the cranial nerves located close to the fourth ventricle These cranial nerves are CN 5 6 and 7 b Pons Respiratory Centers which help to control breathing c The pyramidal tract from the cortex passes through the pons on its way to the spinal cord b The cerebellum is located dorsal to the fourth ventricle and the pons 1 Introduction a The cerebellum makes up 11 of the brain s mass b It is located posterioinferior to the cerebrum and dorsal to the pons and medulla oblongata 2 Structure and Function a The cerebellum has two hemispheres 1The two cerebellar hemispheres are connected by the vermis b The cerebellum has three layers to it as does the cerebrum in amniotes 1Cerebellar Cortex an outer layer of gray matter a As in the case of the cerebral cortex the cerebellar cortex is arranged into folds b The cerebellar cortex determines how smooth our body s movements are 2 Cerebellar White Matter the middle layer it contains axons carrying information to and from the cerebellar cortex 3 Deep Cerebellar Nuclei the inner layer it contains the cell bodies belonging to the axons carrying information to and from the cerebellar cortex 3 The cerebellum communicates with other portions of the brain through the Cerebellar Peduncles a Superior Cerebellar Peduncles connect the cerebellum to the midbrain and carry instructions from the cerebellum to the cerebral cortex b Middle Cerebellar Peduncles connect the cerebellum to the pons and carry instructions from the cerebral cortex motor to the nuclei of the pons c lnferior Cerebellar Peduncles connect the cerebellum to the medulla oblongata and spinal cord and carry information on balance and equilibrium 4 The cerebellum serves to receive and preview intended movements ordered by the cerebral motor cortex a It coordinates the movements of the body 5 Unlike the cerebrum the cerebellum is ipsilateral c The Midbrain39 the Mesencebhalon 1 The midbrain is located between the diencephalon and the pons 2 The midbrain pons and medulla collectively make up the brain stem 3 The Organization of the Midbrain a The midbrain is divided into a roof and a floor by the cerebral aqueduct 1 The floor is made up of the Cerebral Peduncles which contains the fibers of the pyramidal tract 2 The roof is called the Tectum a It has four clusters of nuclei embedded in its white matter called the Corpora Quadrigemina This can be divided into two groups of nuclei 1Superior Colliculi or visual tectum responsible for the visual reflexes 2 lnferior Colliculi or auditory tectum responsible for the auditory reflexes b Surrounding the cerebral aqueduct is gray matter forming the Periaqueductal Gray Matter 1 The periaqueductal gray matter contains the cell bodies of cranial nerve 3 oculomotor and cranial nerve 4 trochlear d The Diencephalon of the Forebrain 1 The diencephalon is the central core of the forebrain and is surrounded by the cerebral hemispheres a It is mostly composed of three paired structures thalamus hypothalamus and epithalamus b It borders the third ventricle c It is made up primarily of gray matter 2 The Thalamus aThe thalamus makes up 80 of the diencephalon b There are two thalamic hemispheres separated by the third ventricle and connected by the Intermediate Mass a commissure c The thalamus serves as a relay center between the cerebrum and the rest of the nervous system 1 It both relays and processes information 2 The thalamus has 12 major nuclei collectively termed Relay Nuclei which allow it to perform this function 3 The Hypothalamus a The hypothalamus forms the inferior diencephalon b It is the main visceral control center of the body 1 This is also facilitated by 12 major nuclei 2 The hypothalamic functions include a control of the ANS b center of emotional response c regulation of body temperature d has centers monitoring hunger and thirst e circadian rhythms f control of the endocrine system 4 The Epithalamus aThe epithalamus forms the dorsalmost portion of the diencephalon b It is composed of a tiny group of nuclei and the unpaired Pineal Gland 1 The pineal gland or epiphysis cerebrei is an endocrine organ a It secrete seratonin and melatonin which is also involved in our circadian rhythms e The Cerebrum or Telencephalon of the Forebrain 1 The vertebrate telencephalon or cerebrum is a paired structure divided into a right and left Cerebral Hemisphere a Extending anteriorly from each hemisphere is the Olfactory Bulb and Tract 1 ln vertebrates that rely primarily on olfaction the olfactory structures will be very well developed a Ex in most sharks the olfactory bulbs tracts lobes and accessory structures are large than is the rest of the cerebrum b Ex primates being more visually oriented have a relatively rudimentary olfactory apparatus 2 The Cerebrum in Fishes a The cerebrum of fish consists of 1 Pallium is a primitive sensory and association area a It receives and processes information from the olfactory mucosa and to a lesser degree from the thalamus 2 Globus Pallidus is a motor area located below the pallium 1 It receives input from the pallium and thalamus and sends motor output to the cranial and spinal nerves 3 The Cerebrum in Amphibians a The amphibian cerebrum like that of fishes has a pallium and a globus pallidus 1 In amniotes these two structures will be dramatically reduced in size and function as new cerebral nuclei take over their functions b In addition to these two structures other nuclei will exist in amphibian cerebrums 1 These cerebral nuclei develop beneath the pallium and allow the cerebrum to participate more extensively in coordinating incoming sensory information and in directing somatic motor output a In amphibians the somatic muscles controlled by these nuclei include appendicular muscles 4 The Cerebrum of Reptiles a The reptilian cerebrum has increased in size significantly over that of the amphibian 1 The hemispheres bulge laterally dorsally and posteriorly over the diencephalon a The thalamus can no longer be seen b One factor increasing the size of the reptilian cerebrum is the development of the Dorsal Ventricular Ridge 1 The dorsal ventricular ridge is an elevation of the cerebrum which is rich in association neurons 2 It receives visual auditory and somatosensory input relayed from the thalamus 3 It processes this information and sends out impulses to the globus pallidus and to other nuclei of the region located below the pallium and termed the Subpallium a The globus pallidus and the nuclei of the subpallium collectively are known as the Striatum in amniotes 1The striatum is named for the striated appearance of fiber tracts traveling through it c Another factor increasing the size of the reptilian cerebrum is an increase in the number of motor neurons for the musculature of the neck and increasing limb musculature Only amniotes have necks 5 The Cerebrum of Birds a The avian cerebrum is similar to that of reptiles having a dorsal ventricular ridge and a striatum b In addition another layer of neurons has been added on top of the dorsal ventricular ridge 1 This elevation of neurons is often called the Avian Ridge 6 The Cerebrum of Mammals a Like the cerebellum the cerebrum has an outer layer of grey matter surrounding a central core of grey matter into which small clusters of grey matter will be found 1 The outer layer of grey matter is called the Cerebral Cortex or Neocortex a It has numerous elevations and depressions on its surface so as to increase surface area 1 Some terminology a Gyrus is the term for a cortical elevation b Sulcus is the term for a shallow cortical depression c Fissure is the term for a deep cortical depression 2 Gyri and sulci are lacking in monotremes some marsupials and many rodent species b The cerebral cortex is rich in neuron cell bodies ex 13 billion are found in the human cerebral cortex c The neocortex is divided up into five major lobes Frontal Parietal Temporal Occipital and lnsula per hemisphere d The neocortex has three major functions 1 It receives sensory input and processes it 2 It initiates the motor output for voluntary motor activities 3 It stores and evaluates sensory input as memory in association areas 2 The central core of white matter primarily consists of myelinated axons serving to conduct information to and from the neocortex to and from the rest of the CNS a The white matter is sometimes referred to as the Internal Capsule b There are 3 functional classes of fiber tracts traveling through the internal capsule 1Commissural Fibers connect the two hemispheres a Ex corpus callosum 2 Association Fibers connect portions of the same hemisphere 3 Pro39ection Fibers connect the cerebral cortex to the rest of the CNS 3 Located within the white matter of the cerebrum are clusters of grey matter called Basal Ganglia Basal Nuclei Cerebral Nuclei or Basal Nuclei a The nuclei are cell bodies that during development migrate from the cortex into the internal capsule b The cerebral nuclei control the intensity and initiation of somatic muscle actions c Cerebral nuclei include the Caudate Nucleus Putamen and Amygdaloid Nucleus 1These nuclei are part of the mammalian striatum b Other evolutionary developments include 1 The globus pallidum has been mostlyfunctionally replaced and has been reduced to a small structure buried deep in the hemispheres 2 The olfactory portion of the pallium has been maintained in mammals as the Hippocampus of the temporal lobe a The rest of the pallium has been lost overall f The Blood Supply of the brain 1 Arterial Flow a The internal carotid arteries andor ventral spinal arteries will carry oxygenated blood to the brain b The vertebral arteries of mammals birds and many reptiles will join to form the basilar artery on the underside of the brain c Communicating arteries will connect the basilar and internal carotid arteries in mammals ad also some other vertebrates to form the Circle of Willis 1 The circle of Willis encircles the base of the diencephalon d The internal carotids supply the cerebrum and the basilar arteries supply the brain stem primarily 2 Venous Drainage a Brains are drained by venous sinuses ex superior sagittal sinus of mammals and small veins that in turn will drain into the internal jugular veins 3 The Choroid Plexus a The choroid plexus is a specialized capillary bed 1 The capillaries are discontinuous so as to allow for increased permeability a This allows for the production of Cerbrospinal Fluid 1CSF is a plasma filtrate that fills the ventricles and central canal as well as being held within the meninges 2 CSF nourishes the brain removes waste protects the brain from mechanical trauma and decreases the weight of the brain 3 CSF is drained by the venous system of the brain b In mammals the choroid plexus is located in the third and fourth ventricles 2 Cranial Nerves a Cranial nerves are paired nerves whose perikarya are located in the brain primarily the brain stem 1 They innervate the structures of the head and neck with one exception 2 The number of cranial nerve pairs varies with the species a Ex humans have 12 pairs of cranial nerves 1 It was from humans that the cranial nerve numerical system was developed a CN 1 is the most anterior cranial nerve and CN 12 is the most posterior 3 Some cranial nerves are sensory some are motor and some carry both b The Cranial Nerves 1 CN 0 The Terminal Nerve Sensory a CN 0 travels alongside of the olfactory tract and innervates the nasal mucosa 1 It arises from the forebrain b It is sensory and may serve in pheromone reception particularly the pheromones tied in to reproduction c CN 0 is found in all gnathostomes even humans 1 It was discovered many years after the 12 cranial nerve pairs had been identified in humans a Since it is anterior to ON 1 it had to be numbered CN 0 2 CN 1 The Olfactory Nerve Sensory a The olfactory nerve innervates the olfactory mucosa where it picks up scent information b CN 1 arise from the forebrain c The number of nerve fibers in ON 1 and the relative surface area of the olfactory mucosa ties in to the role of olfaction in the species 3 CN VN39 The Vomeronasal Nerve Sensory a The vomeronasal nerve is chemoreceptive and most likely detects pheromones b CN VN arises from the forebrain c It is associated with an accessory olfactory bulb and the vomeronasal organ which is located in the nasal cavity 4 CN 239 The Optic Nerve Sensory a CN 2 picks up visual input from the brain b It arises from the forebrain 1 CN 2 crosses below the diencephalon at a point called the ow Chiasma This is the decussation point of the optic nerve fibers a In nonmammals all of the fibers decussate b In mammals the half of the fibers from the medial eye field decussate and the half from the lateral eye field do not 5 CN E39 The Epiphyseal Comple Sensory a CN E receives sensory input from the pineal gland or parietal eye 1 It is only found in some fishes some amphibians and some reptiles b It arises from the forebrain 6 CN 339 The Oculomotor Nerve Motor a CN 3 controls the movements of 4 of the 6 extrinsic ocular muscles 1 CN 3 arises from the midbrain 7 CN P39 The Profundus Nerve Sensory a The profundus nerve is found only in primitive vertebrates b When present it is a separate sensory branch from the trigeminal nerve 1 It plays a role in the detection of cutaneous sensation from the head c It arises from the pons 8 CN 439 The Trochlear Nerve Motor a CN 4 is responsible for the movements of 1 pair of the 6 pairs of extrinsic ocular muscles b CN 4 arises from the midbrain 9 CN 539 The Trigeminal Nerve Both a The trigeminal nerve carries sensory information for cutaneous sensation of the head and also carries motor information to the muscles of mastication b It arises from the pons 10 CN 639 The Abducens Nerve Motor a The abducens controls one pair of the 6 pairs of extrinsic ocular muscles b CN 6 arises from the pons 11 CN 739 The Facial Nerve Both a CN 7 carries sensory information for some of taste sensation and conveys motor information to the muscles of facial expression b CN 7 arises from the pons 12 ON ALL39 The Anterior Lateral Line Nerve Sensory a ON ALL has three branches that will pick up sensory input from the anterior portion of the lateral line 1 It is found in fishes and aquatic state amphibians that possess a lateral line b ON ALL arises from the diencephalon 13 CN 839 The Vestibulocochlear Nerve Sensory a CN 8 picks up information from the auditory and equilibrium sensing regions of the internal ear b CN 8 arises from the medulla oblongata 14 CN PLL39 The Posterior Lateral Line Nerve Sensory a CN PLL has three branches that will pick up sensory input from the posterior portion of the lateral line 1 It is found in fishes and aquatic state amphibians that possess a lateral line b CN PLL arises from the diencephalon 15 CN 939 The Glossopharyngeal Nerve Both a CN 9 carries sensory information for some aspects of taste and for the general sensation of the tongue and pharynx CN 9 also conveys motor information for the control of the tongue and pharynx b CN 9 arises from the medulla oblongata 16 CN 1039 The Vagus Nerve Both a The vagus nerve has a great number of functions and serves to innervate structures throughout the entire body 1 Among its many functions it plays a role in the ANS as a parasympathetic nerve b CN 10 arises from the medulla oblongata 17 CN 11 39 The Accessorv or Spinal Accessorv Nerve Motor a CN 11 acts an accessory to the vagus nerve in the head and neck b CN 11 arises from the medulla oblongata c CN 11 is onlyfound in tetrapods 18 CN 1239 The Hypoglossal Nerve Motor a CN 12 plays a role in the innervation of the tongue muscles b CN 12 arises from the medulla oblongata c CN 12 is found only in tetrapods E The Autonomic Nervous System 1 The ANS controls the visceral organ musculature and glands a It uses a two neuron relay system 1 Preganglionic Neuron a The preganglionic nerve is a myelinated nerve which arises from the CNS and sends ANS information towards the ANS ganglion 2 Postanglionic Neuron a The postganglionic nerve is an unmyelinated nerve which arises from the ANS ganglion and send ANS information tow the target organ b There are two functional subdivisions the Sympathetic and the Parasympathetic Divisions 1 The two subdivisions typically will innervate the same organs but will elicit different responses due to differences in the neurotransmitter used a The sympathetic division uses epinephrine and norepinepherine adrenaline and noradrenaline to communicate between the postganglionic nerve and the target organ 1 It is Adrenergic b The parasympathetic division uses acetylcholine to communicate between the postganglionic nerve and the target organ 1 It is Cholinergic 2 The Sympathetic Division a The sympathetic division causes the flight fright and fight response 1 It allows for response to emergencies b The sympathetic division arises from the thoracic and from some of the lumbar spinal nerves 1 Ex in humans it arises from T1 through L2 2 For this reason the origin of the sympathetic division is said to be Thoracolumbar c The sympathetic division has three types of ganglia 1 Chain Ganglia are paired structures located parallel to the vertebral column a The chain ganglia on one side are linked by nerve trunks to form a Sympathetic Trunk 2 Prevetebral Ganglia are singular structures located ventral to the vertebral column 3 Adrenal Medulla the central portion of the adrenal gland is actually a sympathetic ganglion a It receives axons from Preganglionic nerves b It cells secrete neurotransmitters into the blood stream 3 The Parasympathetic Division a The parasympathetic division is sometimes called the housekeeping division 1 It causes a decrease in heart rate breathing rate and an increase in blood flow to the digestive and excretory organs b It arises from the cranial nerves and the sacral spinal nerves 1 As a result its origin is said to be Craniosacral c The parasympathetic ganglia are located near or in the target organs 1 As a result the axons of the postganglionic nerves are short 2 ex Myenteric plexus submucosal plexus Case Study The Cerebral Cortex in Higher Primates 1 Introduction a The cerebral cortex is the center of our consciousness b It is a layer of gray matter covering the exterior of the cerebrum 1 It is only 2 to 4 mm thick but due to its numerous convolutions it accounts for 40 of the brain s total mass c The cortex has Domains of specific cortical functioning 1 The domains however are not necessarily isolated and may overlap with one another 2 The Motor Areas of the Cortex are located in the posterior portion of the frontal lobe There are four motor domains a Primary Motor Cortex or Somatic Motor Area 1 It is located along the precentral gyrus anterior to the central sulcus of the frontal lobe 2 It controls the voluntary and skill requiring actions of the limbs trunk etc a 80 it initiates most skeletal muscle activity 3 The axons of the primary motor cortex run Contralateral meaning that the left hemisphere s primary motor cortex controls the muscular activity of the right body a These axons are the processes of large cerebral neurons called Pyramidal Cells b The axons extend throughout the brain as they carry motor information towards the spinal cord and are called the Pyramidal Tract or Corticospinal tract 4 The human body is spatially represented on the primary motor cortex a The term for this body mapping is Somatotropy b Premotor Cortex 1 The premotor cortex is located immediately anterior to the primary motor cortex 2 It serves as a memory bank for learned or skill requiring motor activities c Frontal Eye Field 1 The frontal eye field is located anterior to the premotor cortex 2 It controls the skeletal muscles producing movements of the eyes d Brocca s Area 1 Brocca s area is located anterior to the inferior extension of the premotor cortex 2 Its purpose is not clear a It was once believed to control only the motor aspects of speech That is now considered to be incorrect b Now it is believed to be the means that our brain uses to preplan all of our voluntary motor activities 1 Studies have shown it to become stimulated prior to all motor activities 3 The Sensory Areas of the Cortex are located on the occipital parietal and temporal lobes Each major sense has its own domain a Primary Somatosensory Cortex 1 It is located posterior to the central sulcus on the postcentral gyrus of the parietal lobe 2 It is involved in our conscious awareness of somatosensory input a The somatosenses are those of the outer body particularly the skin such as pain pressure touch vibration temperature and proprioception b It has the ability to determine precisely where on the body the stimulation was perceived 1This is termed Spatial Discrimination 3 Like the primary motor area the primary somatosensory area displays a somatotropy b contralateral b Somatosensory Association Area 1 This domain is located immediately posterior to the primary somatosensory area 2 It serves to integrate different somatosensory inputs into a comprehensive evaluation of what is producing those stimuli a This is possible due to heavy integration between the somatosensory association area and primary somatosensory area b In effect it serves as a memory bank allowing us to evaluate somatosensory input based on past experiences c Visual Area 1 The visual area is divided into the primary visual cortex and the visual association area 2 The Primary Visual Cortex receives visual stimuli from the eyes a It is located on the extreme posterior and medial aspects of the occipital lobe 3 The Visual Association Area interprets and evaluates the visual input received by the primary visual cortex based on past experiences a Located over most of the occipital lobe d Auditory Area 1 The auditory area is also divided into the primary auditory cortex and the auditory association area 2 The Primary Auditory Complex receives auditory stimuli from the ears a It is located on the superior edge of the temporal lobe mainly within the lateral sulcus 3 The Auditory Association Area interprets and evaluates the auditory input received based on past experiences a It is located posterior to the primary auditory complex e Gustatory Complex 1 The gustatory complex is located on the roof of the lateral sulcus 2 It is responsible for our conscious awareness and interpretation of taste f Olfactory Cortex 1 It is located in the Piriform Lobe of the medial cerebral aspect 2 The olfactory cortex is responsible for our conscious awareness and interpretation of smell 4 Association Areas of the Cortex association areas make up the remainder of the cortex They integrate different senses and experiences with past ones a We have already seen three somatosensory association area visual association area and auditory association area b Prefrontal Cortex 1 It is located anterior to the motor areas on the frontal lobe 2 The prefrontal cortex is responsible for personality and cognition our ability to learn c General Interpretation Area or Gnostic Area 1 It is ill defined and located on large areas the temporal parietal and occipital lobes a However usually it is only found on one hemisphere and generally that is the left one 2 It serves to integrate all of our sensory input to give a comprehensive understanding of the situation a It signals the prefrontal cortex which can allow for an emotional response as well d Language Comprehension Area allows us to understand language e Visceral Association Area allows for our conscious perception of visceral sensory information 5 The Hemispheres and Cortical Functioninq a It is currently believed that there is a division of labor between the two hemispheres 1 Remember that the two hemispheres are contralateral controlling opposite sides of the body 2 They specialize to an extent on the cognitive functions a Left Hemisphere responsible for logic math amp language b Right Hemisphere responsible for emotion intuition artistic skills and visualspatial skills in most Chapter 17 The Sense Organs A Introduction 1 Sensory receptors can be divided up in two ways a Visceral vs Somatic Senses 1 Visceral receptors monitor the internal environment of the body a Sometimes these receptors are called lnteroceptors b Visceral senses include nausea and hunger 2 Somatic senses monitor the external environment and the external body or soma a These receptors include Exteroceptors and Proprioceptors b Somatic senses include the sensation of air temperature and muscle strain b General vs Special Senses 1 General senses have their receptors spread out over a large area a Ex touch pressure temperature pain b In mammals the location of the stimulus that has produced the sensation is determined by the sensory cortex c There are General Somatic and General Visceral senses 2 Special senses have their receptors concentrated in a small area a Ex sight smell taste hearing equilibrium b In mammals the location of the stimulus that has produced the sensation is determined by the sensory cortex c There are Special Somatic sight smell hearing amp equilibrium and Special Visceral taste senses 2 Sense reception can be handled by either the dendritic endings of sensory neurons or by an entire receptor cell a Dendritic Endings branch from sensory neurons and invade the tissues during development 1 All senses detected by dendritic endings are general senses 2 There are two forms of dendritic endings a Encapsulated Dendritic Endings have the tip of each dendritic ending encased in a multilayered connective tissue capsule 1 This arrangement increases surface area for increased sense perception b Free Dendritic Endings lack the ct capsules on the tips of the dendrites the tips of the dendrites are naked b Complete Cell Receptor Cells utilize the entire cell to detect stimuli 1 All senses detected by receptor cells are special senses 2 Complete cell receptor cells can be either neurons ex olfaction or neuroepithelial cells ex hearing a Neuroepithelial cells are specialized epithelial cells derived from neural crest ectoderm 1 Neuroepithelial cells can conduct an impulse to a sensory neuron 2 To detect stimuli many neuroepithelial cells will have hairlike structures called Stereocilia on the apical surface a Due to the hairlike appearance of stereocilia these neuroepithelial cells are sometimes referred to as hair cells B Special Somatic Receptors 1 Neuromast Organs of Fishes and Aquatic Amphibians a Neuromast cells are neuroepithelial cells and display the typical arrangement 1 These hair cells are associated with columnar epithelial cells that surround and protect them called Sustentacular or Supporting Cells 2 The neuroepithelial cells have hairlike stereocilia that detect the stimuli a The stereocilia are embedded in an acellular glycoprotein called a Cupola 3 In the connective tissue underlying the neuroepithelial cells and supporting cells are sensory dendrites that will carry the impulse from the neuroepithelial cells to the CNS b Neuromast cell is fish and aquatic amphibians principally monitor mechanical stimuli from water c Neuromast cells can be either external or internal 1 External Neuromasts are located in shallow pits or grooves on the body surface with the cupola of the neuromast cells projecting into the water a The external neuromast is considered to be a primitive state neuromast b They are found in agnathans larval amphibians and aquatic urodeles 2 Internal Neuromasts are more specialized structures having the cupola embedded to some extent within the body a The most specialized internal neuromasts of all are located in the membranous labyrinth of the inner ear in all gnathostomes d Neuromasts can be found in a number of locations in jawed fishes 1 Pit Organs are fluid filled pits located beneath the epidermis a These are internal neuromasts embedded in the skin that open onto the surface by way of a pore 1 They are primarily located on the head 2 Ampullae of Lorenzini are internal neuromasts of sharks located deep beneath the surface of the skin a They open up onto the surface by means of a long duct 1 The duct and the area immediately around the neuromasts has a gelatinous material called jelly a This jelly is produced by the supporting cells of the neuromast b They are primarily located on the head c Ampullae of Lorenzini are electroreceptive and aid in the detection of prey 3 The Lateral Line and Cephalic Canal Systems a In their simplest form lateral line and cephalic canal systems are shallow grooves on the surface of the head and a single groove extending along the lateral line to the tail on both sides 1 In the primitive state the neuromasts of the lateral line and cephalic canal systems are external neuromasts a The lateral line and cephalic canal systems are lost in larval amphibians when they metamorphosize into the adult terrestrial form 2 ln jawed fishes the lateral line and cephalic canal systems neuromasts are internal neuromasts a In most teleosts the lateral line canal has sunk below the surface and is now embedded in the dermal bone b Lateral line and cephalic canal systems respond to mechanical forces such as water currents 1 They allow fish to avoid predators detect the movements of prey especially in blind species school orientate in flowing streams called rheotaxis and a number of other functions 2 In some species some portions of these canals are also able to respond to electrical signals and so are electroreceptive c They are innervated in fish larval aquatic amphibians and adult aquatic amphibians by CN 8 CN ALL and CN PLL 1 ln amniotes the innervation of neuromasts by CN remains since there are internal neuromasts in the ear 2 The Membranous Labyrinth of the Ear a The membranous labyrinth is found in all vertebrates It is located within a bony or cartilaginous labyrinth in the otic capsule of the neurocranium 1 In most fishes it serves only in the detection of equilibrium but in some fishes and all tetrapods it detects audition as well as equilibrium b The Basic Structure of the Membranous Labyrinth 1 The membranous labyrinth is located within a skeletal labyrinth composed of either cartilage or bone a In all gnathostomes there are at least two portion to this skeletal labyrinth Semicircular Canals and the Vestibule 1 Mammals and birds have three portions to this skeletal labyrinth Semicircular Canals the Vestibule and the Cochlea a The cochlea developed from an outpocketing of the vestibule in fish and amphibians called the Lagena 2 Between the skeletal and membranous labyrinths is a layer of fluid called Perilymph a The space that encloses this fluid the space between the two labyrinths is called the Perilymphatic Space 3 The membranous labyrinth has two regions in most gnathostomes and three regions in mammals a Semicircular Ducts are located within the semicircular canals 1 Gnathostomes have three semicircular ducts and canals one in each plane of motion while agnathans have two b Within the vestibule are two connected portions of the membranous labyrinth called the Utricle and Saccule c The Cochlear Duct is located in the cochlea of birds and mammals 4 The membranous labyrinth is hollow and filed with a fluid called Endolymph a Most vertebrates have an Endolymphatic Duct extending from the vestibule and ending in a blind sac called the Endolymphatic Sac 1 ln elasmobranchs the endolymphatic ducts open on to the surface of the chondrocranium and are located in depressions termed the Endolymphatic Fossae 2 In mammals the Endolymphatic sacs and also a set of perilymphatic sacs are located in the subarachnoid space c Functional Roles of the Membranous Labyrinth 1 The Vestibule and Mechanism of Static Eguilibrium a The receptors of static equilibrium are located in the utricle and saccule of the vestibular portion off the bony labyrinth 1 They provide sensory information regarding the orientation of the head in space and as a result help us to maintain posture b The receptors are located in the Macula meaning spot on the wall of the utricle and saccule 1 The maculae consist of two classes of epithelial cells Supporting Cells and Hair Cells a The hair cells aka receptor cells have long stereocilia which extend into an overlying acellular membrane 1This membrane is called the Otolith Membrane b The supporting cells are the typical columnar epithelial cells 1They secrete the otolith membrane which is a gelatinous glycoprotein containing calcium carbonate crystals called Otoliths in amniotes and some fishes a They are composed of bone in some fishes c The otoliths move due to movements of the head 1 Their extra mass is more susceptible to gravitational forces 2 As the otoliths move their mass moves the otolith membrane 3 The membrane will then press down on the stereocilia triggering a nerve impulse 4 The impulse is transmitted along the vestibular branch of CN 8 to the cerebral cortex 2 The Semicircular Canals and Mechanism of Dynamic Eguilibrium a The receptors of dynamic equilibrium are located in the Ampulla of the semicircular canal portion off the bony labyrinth 1 They provide sensory information regarding the orientation of the head in space when we are moving b In mammals and birds the three semicircular ducts in the semicircular canals are positioned at right angles to one another allowing for the detection of dynamic equilibrium along three planes 1 The frontal plane is handled by the superior semicircular canal 2 The sagittal plane is handled by the posterior semicircular canal 3 The transverselateral plane is handled by the lateral semicircular canal c Within each ampulla is the sensory organ for dynamic equilibrium It is called the Crista Ampullaris 1 Microscopically the three cristae resemble the organ of Corti a It has two classes of epithelial cells Supporting Cells and HairReceptor Cells b The hair cells have long stereocilia embedded in an acellular gelatinous membrane called the cupola 2 When the head moves the endolymph flows in the semicircular ducts a It will push against the cupola which in turn presses against the stereocilia of the hair cells b The bending of the stereocilia will stimulate and impulse to travel to the vestibular branch of CN 8 and to the cortex 3 The Cochlea and the Mechanism of Audition a The cochlea is a spiral shaped portion of the bony labyrinth located anterior to the vestibule b Internally the cochlea is divided into three canals Scala Vestibuli Scala Tympani and between them Scala Media 1 The scala media is also called the Cochlear Duct and houses the sensory structure responsible for hearing a It is separated from the scala vestibuli by the Vestibular Membrane b It is separated from the scala tympani by the Basilar Membrane c In the cochlear duct on the basilar membrane is the Organ of m aka Spiral Organ the organ of hearing 1 The organ of Corti consists of a series of epithelial cells located on the inner surface of the basilar membrane a One of the two classes of epithelial cells is the supporting cells b The other class is the neuroepithelial Hair Cells or auditory receptor cells 1There are two types Outer and Inner Hair Cells 2 They have long stereocilia called hairs which extend into an acellular membranous structure called the Tectorial Membrane 3 The basal ends of the hair cells are in contact with the cochlear branch of CN 8 2 Vibrations due to sound waves traveling through the endolymph and perilymph cause the basilar and tectorial membranes to rise and fall This results in the compression of the stereocila against the tectorial membrane and the production of an impulse c The Cochlear Duct and the Evolution of the Cochlea 1 Although the cochlea is limited to birds and mammals other vertebrates do posses a mechanism for hearing a The mechanism of hearing in some fishes 1 Cypriniformes use Weberian ossicles to transmit sound waves to the lagena a Sound waves traveling through the water transmit wave energy to gases located in the swim bladder This wave energy is then transferred from the bladder to the membranous labyrinth by Weberian Ossicles 1 Weberian ossicles are modifications of the transverse processes of the first 3 or 4 vertebrae 2 Clupeiformes use an extension of the swim bladder to transmit sound waves to the lagena a The swim bladder has an anterior extension that touches the labyrinth allowing for the transmission of sound energy to the lagena b The mechanism of hearing in amphibians and reptiles 1 ln amphibians and reptiles in addition to the normal macula there is a modified macula located in the sacculus near the lagena that allows for audition 2 Amphibians possess two special maculae in the sacculus a These maculae are called the Amphibian and Basal Papillae 1 Instead of having an otolith membrane these special maculae have a tectorial membrane that will stimulate the stereocilia due to sound waves 3 Reptiles have an expanded lagena and their basal papilla has grown into it a As in amphibians this basal papillae has a tectorial membrane and functions for hearing 2 The arrangement of lagena and basal papilla of the typical reptile has been modified in other amniotes a In crocodilians birds and monotreme mammals the basal papilla has become fully engulfed within the lagena to form an Organ of Corti b In marsupial and placental mammals the lagena has become extremely elongated grows around the Modiolus bone to form the snail shell shaped cochlea 3 To aid the membranous labyrinth of the ear with audition tetrapods have a Middle and an Outer Ear a The Outer or External Ear 1 The external ear is designed to collect sounds and to direct them inward a In mammals the external ear consists of the pinna external auditory canal and tympanic membrane 1The Pinna is composed mostly of elastic cartilage covered by thick skin a It is present in most but not all mammals b It serves to capture and to concentrate sound waves 2 The External Auditory Canal is located within the petrous portion of the temporal bone a It is a tube leading from the pinna to the tympanic membrane b The walls of this tube are composed of bone lined by elastic cartilage extending from the pinna 1The elastic cartilage in turn is covered by thin very sensitive skin c At the opening of the external auditory canal the skin contains Ceruminous Glands and a few hair follicles which serve to protect the ear from foreign invaders 3 The Tympanic Membrane is a thin semitransparent membrane composed of fibrous connective tissue located between the external auditory canal and the middle ear b Birds crocodilians and some specialized lizards have an external auditory canal and a tympanic membrane c Other reptiles and many amphibians have the tympanic membrane laying flush with the surface of the head 1They lack and external auditory canal d Some amphibians sphenodon and limbless reptiles lack a tympanic membrane 1Sound and seismic waves are conveyed towards the ear in a few different ways the most common being transmission via the jaw b The Middle Ear or Tympanic Cavity 1 The middle ear is located in the temporal bone and receives sound waves conducted from the tympanic membrane in most vertebrates a It is separated from the external ear or the external environment by the tympanic membrane b It is separated from the inner ear by a thin bony partition containing two openings the Round Window and the M Window which has the second tympanic membrane c In all tetrapods the anterior wall of the middle ear contains an opening which leads into the Eustachian Tube aka auditory tube 1The eustachian tube connects the middle ear to the pharynx and helps to equalize air pressure in the head 2 It evolved from the spiracle of fishes 2 Sound waves are conveyed across the middle ear from the tympanic membrane to the oval window by means of one or more ossicles a All tetrapods have the Columnella or Stapes as it is known in mammals which sits against the oval window 1To aid the columnella birds reptiles and amphibians also have a cartilaginous or bony complex called the Extracolumnella which is attached to the tympanic membrane on one end and the columnella on the other b Mammals have three small bones called the Auditory Ossicles 1The three ossicles are sequentially arranged from the tympanic membrane to the oval window aka fenestra vestibuli Malleus lncus and Stages a As discussed previously the malleus and incus evolved from bones of the reptilian jaw 2 There are some muscles associated with the mammalian ossicles a The Tensor Tympani Muscle increase tension on the tympanic membrane by pulling the malleus medially 1 It prevents damage to the inner ear due to loud sounds b The Stapedius Muscle draws the stapes posteriorly against the annular ligament to also protect the inner ear from loud sounds 1 It is the smallest skeletal muscle of the body 2 It passes through the opening of the stapes and is why the mammalian columnella has its characteristic stirruplike shape d Echolocation 1 Certain mammals possess the ability to project sound waves and form an image based on the reflection of these sound waves This is echolocation a It is found in whales bats some shrews and even a few species of blind mammals 3 Vision a Accessory Structures of the Lateral Eye 1 Eyelids or Palpebrae are found in amniotes a Functions 1 shade eyes from excessive light 2 protect the eyes when sleeping 3 protect the eyes from foreign objects d distribute lubricating secretions over the eyeballs b Features of the Palpebrae a The upper eyelid is termed the Superior Palpebra b The lower eyelid is termed the lnferior Palpebra c Nictitating Membranes are a third transparent eyelid found in many vertebrates 1 They also protect the eye a Ex sharks attacking prey will have the nictitating membrane close immediately prior to contact 2 They are histologically distinct from the other palpebrae 2 Eyelashes are found in mammals and birds primarily a The eyelashes of the superior palpebra are longer than are those of the inferior palpebra b Eyelashes help to protect the eye from particulate matter c At the base of each eyelash follicle is a gland which secretes a lubricant for the eyelashes These glands are the Glands of Zeis 3 The Lacrimal Apparatus is found in tetrapods a The structures of the lacrimal apparatus serve to manufacture to distribute and to drain the tears 1 The Lacrimal Gland produces lacrimal fluid a Lacrimal Fluid aka tears serves to lubricate the eye and to help remove particulate matter 2 The two lacrimal sacs are located in the lacrimal sulci of the lacrimal bones and serve to drain lacrimal fluid from the orbit aThey receive lacrimal fluid from the lacrimal canals and pass it on to the nasolacrimal duct b The nasolacrimal duct passes through the nasolacrimal canal into the posterior nasal cavity 1 It carries lacrimal fluid into the posterior nasal cavity 3 Lacrimal fluid is spread over the eye by the blinking of the palpebrae b In species possessing a nictitating membrane there is an extra component to the lacrimal apparatus called Harderian Gland 1 Harderian glands serve to lubricate the nictitating membrane 4 The Extrinsic Ocular Muscles are 6 skeletal muscles which originate outside of the eye and serve to move the eye They are pretty much the same for all vertebrates a The Rectus Muscles 1 lnferior Rectus lt attaches to the inferior eyeball a It depresses the eye 2 Superior Rectus lt attaches to the superior eyeball a It elevates the eye 3 Medial Rectus lt attaches to the medial eyeball a It turns the eye medially 4 Lateral Rectus lt attaches to the lateral eyeball a It turns the eye laterally b The Oblique Muscles 1 Superior Oblique lt attaches to the superior eyeball a It turns the eye laterally and depresses it inferiorly 2 lnferior Oblique lt attaches to the inferior eyeball a It turns the eye medially and elevates it b The Lateral Eve Structure and Function 1 The eyeball can be divided into three layers or tunics the fibrous tunic the vascular tunic and the nervous tunic a The Fibrous Tunic 1 The fibrous tunic is superficialmost layer of the eyeball 2 It is composed of a tough fibrous connective tissue 3 The fibrous tunic can be divided into two portions a The Sclera makes up the posterior four fifths of the fibrous tunic 1 It is an opaque white layer 2 The sclera gives shape to the eyeball protects the eyeball and serves as the point of attachment of the extrinsic ocular muscles 3 A variety of vertebrates have Scleral Plates a Scleral plates are reinforcing osseous or cartilaginous structures b Found in birds ichthyosaurs some deep sea fishes etc a The Cornea makes up the anterior fifth of the fibrous tunic 1The cornea is transparent so as to allow light to enter the eyeball 2 The cornea can be described as an avascular fibrous coat anterior to all other structures of the eyeball b The Vascular Tunic 1 The vascular tunic is also known as the Uvea a It is overall a well vascularized and heavily pigmented tunic 2 The uvea can be divided into three portions a The Choroid which makes up about the posterior four fifths of the uvea 1 It is a thin darkly pigmented and well vascularized tissue lining most of the sclera a The blood vessels of the choroid service the retina 2 The choroid serves to absorb light which has passed through the nervous tunic a This prevents the light from being reflected back and distorting the image 3 In many nocturnal and night active vertebrates the choroid will have a Tapetum Lucideum a This is a structure composed of guanine crystals that reflect light back to the retina so as to increase the amount of photoc stimulation available at night b The Ciliary Body is a portion of the anterior uvea 1 It contains the ciliary muscles which will alter the shape of the lens to allow for accommodation c The E is a structure of variable pigmentation which surrounds the pupil 1The pupil is really a circular opening in the iris 2 It serves to regulate the amount of light passing through the upil a It has both radially and circularly arranged smooth muscles which serve to constrict and to dilate the pupil respectively 3 The iris is connected to the ciliary body c The Nervous Tunic 1 The nervous tunic is found in the posterior eye lining the choroid 2 It has two portions a The Pigmented Epithelium a layer of heavily pigmented columnar epithelial cells laying against the choroid 1 It is considered to be a portion of the choroid by some b The Retina is the true nervous tunic 1 It is actually an outgrowth of the brain a As a result its hold on the eyeball is tenuous being only at the optic disc and the ora serrata 2 The retina serve for image formation a The rest of the eye is basically designed to direct light and to control the amount of light at the retina 3 The retina has a three layered arrangement what is called the trilaminar arrangement a The Photoreceptor Layer the last layer to receive light and the layer in contact with the pigmented epithelium 1 It is made up of neuroepithelial cells called Photoreceptors which respond to light conducting an impulse towards the brain a There are two types of photoreceptors 1 Rods cylindrical in shape respond to lower levels of light allow for black and white vision a Found in all vertebrates b Cones conical in shape need high levels of light for stimulation allow for color vision a Found in only some vertebrates b Different types of cones will contain different photopigments allowing for the detection of different wavelengths b The Bipolar Cell Laye the middle layer 1 It contains a variety of cells but gets its name from the Bipolar Cells a Bipolar cells are sensory neurons which pick up the impulse from the photoreceptors and conduct it towards the brain c Ganglion Cell Layer the first layer to receive light and the furthest from the uvea 1 It contains large neurons called Ganglion Cells which carry the impulse form the bipolar cells towards the brain a Their axons form CN 2 the optic nerve and exit the eyeball at the optic disc 1 This gives us a blind spot in the eyeball 3 The retina will have a variety of topographical features in duplex retinas which are cone rich and the point on which light is focused by the lens aOne is a conical depression filled with the cones called the Fovea or Area Centralis 1 Most animals having a fovea have only one However some species have two ex hawks four eyed fish or three ex some coral reef fishes b Another structure is a linear arrangement of cone rich retina called a Visual Streak c Some species have a combination of fovea and streaks 1 Other Structures of the Lateral Eye a The Lens 1 The lens is a complex structure composed of many layers of protein fibers 2 It serves to receive light and to focus it onto the retina 3 It is held in place by the Suspensory Ligaments which attach to the ciliary body which again allows for accommodation b The Cavities of the Eye 1 The Anterior Segment this is the space anterior to the lens a It is divided by the iris into two subsections 1 Anterior Chamber the portion of the anterior segment between the cornea and the iris 2 Posterior Chamber the portion of the anterior segment between the iris and the lens b The anterior segment contains Aqueous Humor a plasma filtrate 2 The Posterior Segment this is the space posterior to the lens alt is much larger than is the anterior segment b It contains an extremely fluidlike connective tissue called Vitreous Humor 1 It helps to hold the retina in place and helps the eye to withstand pressure b The Parietal or Median Eye 1 The median eye is found in many vertebrates excepting birds and mammals a It is an evagination of the epithalamus 1 Actually there are two evaginations of the epithalamus that together make up the Epiphyseal Complex a The anterior evagination is the Parapineal and the posterior evagination is the Pineal 1 In most vertebrates that possess a median eye the parapineal evagination is the photosensitive one the eye a However in lampreys both are photosensitive 2 Unlike the lateral eyes the median eye does not form a retinal image a Instead the median monitors the duration and intensity of light and so photoperiods 1 It play s a role in establishing circadian rhythms etc 3 In mammals the medial eye has become reduced to a Pineal Gland or Epiphysis Cerebrei a It is an endocrine organ that s secretions are stimulated by light received via the optic nerve 1 Its secretions include seratonin and melatonin a They have numerous functions including setting the biological clock and allowing for normal brain activity 4 Infrared Receptors in Snakes a Members of the snake family Crotalidae have an infrared receptor located in a deep pit between the nostril and the eye 1 The pit is lined by epithelium housing supporting cells and neuroepithelial receptor cells a The stereocilia of these hair cells respond to heat radiation b These pits are called Loreal or Jacobson s Pits b Pythons and some boa species have similar but less sensitive pits among the scales lining the mouth 1 these pits are called Labial Pits c The infrared receptors of snakes are innervated by CN 5 Olfaction a Olfaction and for that matter gustation is a chemoreceptive sense 1 The stimulus is a chemical and it must be in solution for detection a This is one reason for serous secretions in the nasal and oral cavities 01 b In gnathostomes olfactory organs develop from a pair of Olfactory Placodes that arise on the surface of the head and sink into the nasal cavity to forma pair of Nasal Pits during development 1 ln fishes other than lobefins the developing olfactory mucosa will become surrounded by mesenchyme to form a blind olfactory sac a Unlike tetrapods fish use nostrils only for olfaction 2 ln lobefins and tetrapods the olfactory pts push deep into the head to open into the oral cavity or pharynx a These openings become the internal nares b As a result the olfactory mucosa is a portion of the nasal mucosa 1 The amount and distribution of olfactory mucosa varies and will correspond to the sensitivity of the species to olfaction c The Olfactory Mucosa 1 It consists of sustentacular cells and receptor cells a The sustentacular cells are ciliated columnar epithelial cells much like those of the nasal mucosa b The olfactory receptor cells are bipolar neurons 1 The dendrite extends onto the surface of the olfactory mucosa a It has a knob like terminis that gives rise to a number of stereocilia olfactory hairs to detect stimulus 2 The axon extends into the underlying ct a The axons will form bundles called Filia Olfactoria that travel through the olfactory foramina of the cribriform plate of the ethmoid to synapse with Mitral Cells in the olfactory bulbs 1 It is the axons of the mitral cells that form the olfactory nerve 2 Since olfaction is chemoreceptive associated with the olfactory mucosa will be seromucus glands whose secretion will dissolve the olfactory stimuli a These glands are termed Bowman s Glands d The Vomeronasal Organs 1 Many tetrapods have an evagination of the ventral olfactory mucosa that becomes isolated from the rest of the nasal cavity during development a This evagination will become the vomeronasal organ 2 The vomeronasal organ is chemoreceptive a It may respond to food stuffs and or pheromones C Special Visceral Senses 1 Gustation a Taste is picked up by microscopic structures called Taste Buds 1 Taste buds are spherical clusters of sustentacular and taste receptor cells located within the oral mucosa generally a The sustentacular cells are columnar epithelial cells b Taste receptor cells are columnar shaped neuroepithelial cells 1 The apex of these cells will have hair like stereocilia a The stereocilia project through an opening in the mucosa called the Taste Pore to detect taste b In fishes taste buds are distributed overall of the pharyngeal surfaces and in some species even on certain external surfaces 1 ex the whiskers of catfish c In tetrapods the taste buds are typically limited to the tongue posterior palate and oropharynx d Three cranial nerves allow for the perception of taste CN 7 9 and 10 D General Somatic Receptors 1 General somatic receptors are dendritic endings either encapsulated or free and are wide spread in their distribution a There are two categories of general somatic receptors 1 Cutaneous Receptors detect stimuli such as light touch pressure temperature and pain 2 Proprioceptors monitor stress and strain on the skeletal muscles and their associated joints a This information allows an organism to know where its body is in space 1 Equilibrium is only concerned with the location of the head in space E General Visceral Receptors 1 General visceral receptors are typically free dendritic endings which monitor general sensations from the viscera Chapter 18 The Endocrine System A Endocrine Organs That Are Derived From Ectoderm 1 The Pituitary Gland or Hypophysis a The pituitary is located in the sella turcica and suspended from the diencephalon by a stalk like structure called the lnfundibular Stalk 1 The infundibular stalk connects the pituitary to the hypothalamus a It allows the hypothalamus to exert control over the pituitary by a variety of blood borne factors 2 The pituitary produces a number of hormones and has a powerful influence over the body a Some of its hormones will effect other hormone producing organs 1 The term for these hormones is Tmpic 3 The pituitary has two functionally histologically evolutionary and developmentally distinct portions the Adenohypophysis and the Neurohypophysis b The NeurthDophvsis or Posterior Pituitarv 1 The posterior pituitary develops as an outgrowth of the floor of the diencephalon a It will develop into three regions Pars Nervosa Median Eminence and lnfundibular Stalk 2 The posterior pituitary does not produce hormones of its own a Instead it stores hormones produced by the hypothalamus 1 The hypothalamus has specialized neurosecretory cells a These cells are modified neurons b Their axons will pass from the hypothalamus through the infundibulum and into the pars nervosa where the secretions are released 1The secretions are stored as Hering Bodies and are released into capillary beds when needed by the body a These hormones are M and Oxytocin c The Adenohypophysis or Anterior Pituitary 1 The anterior pituitary arises from an evagination of the stomodeum a In amniotes sharks and some bony fishes this evagination is a hollow pouch called Rathke s Pouch b The evagination becomes detached from the stomodeum and attaches to the neurohypophysis 2 The anterior pituitary has three portions Pars Distalis Pars lntermedia and Pars Tuberalis 3 The anterior pituitary is the truly endocrine portion of the pituitary producing a variety of hormones a As a result it is rich in secretory epithelial cells b lts secretions are controlled by chemical factors produced by the hypothalamus 1 These factors travel from the hypothalamus to the pituitary by way of a special circulatory loop called the Hypothalamic Hypophyseal Portal Tract 4 The hormones of the adenohypophysis are Somatotropin GH Thyrotropin TSH Adrenocorticotropin ACTH LH amp FSH Prolactin PRL and Melanoc e Stimulating Hormone MSH 2 The Pineal Gland or Epiphysis Cerebrei a The pineal gland is an evagination of the epithalamus that has developed from the median eye b It produces several hormones and this production is typically based on photic stimulation 1 Two hormones produced by it are a Serotonin for normal brain physiology b Melatonin for establishment for circadian rhthyms 3 Aminoqenic Tissue and the Adrenal Medulla a The tetrapod adrenal gland consists of two distinct tissue components 1 Aminogenic Tissue produces catecholamines and makes up the adrenal medulla in mammals a It is derived from ectoderm 2 Steroidogenic Tissue produces a variety of steroid based hormones and makes up the adrenal cortex a It is derived from mesoderm b Aminogenic Tissues in Fishes and Amphibians 1 Lampreys and elasmobranchs have aminogenic tissue arranged into clusters along the length of the postcardinal veins 2 Hagfish have their aminogenic cells in association with the heart and many major blood vessels 3 Lungfish have their aminogenic tissue located along the dorsal aorta 4 ln teleosts the aminogenic tissue is generally found near the anterior end of the kidneys interspersed amid steroidogenic tissue 5 ln anurans both tissue types are loosely arranged into a diffuse gland on the ventral aspect of the kidney c Aminogenic Tissues in Amniotes 1 Most amniotes have discrete adrenal glands located at or near the cranial aspect of the kidneys a In crocodilians and birds the two tissue types are interspersed within a capsule b In lizards aminogenic tissue encompasses the steroidogenic tissue c In mammals the situation is variable 1 In some such as primates steroidogenic tissue forms a capsule around aminogenic tissue d Aminogenic cells are of the same lineage as are postganglionic neurons of the sympathetic division 1 Both are derived from neural crest ectoderm 2 In effect they are a third type of sympathetic ganglion a They receive axons from preganglionic neurons and produce epinephrineadrenaline and norepinepherinenoradrenaline 1 In the case of the secretion from aminogenic tissue these products are called Sympathomimetic 3 Aminogenic cells are also referred to as Chromaffin Cells B Endocrine Organs That Are Of Mesodermal Derivation 1 Steroidogenic Tissue of the Adrenal Cortex a Steroidogenic tissue is of mesodermal origin 1 Unlike aminogenic tissue that is controlled by preganglionic neurons steroidogenic tissue is controlled by tropic hormones 2 It arises from the genital ridge and underlying nephrogenic mesoderm 3 Steroidogenic cells are epithelial cells as is typical for a gland a Their secretions are termed Corticosteroids since the steroidogenic tissue of the adrenal gland is located in the adrenal cortex b The mammalian steroidogenic tissue forms the cortex of the adrenal gland The cortex has three layers and each layer produces a different group of hormones 1 Zona Glomerulosa is the superficial layer and produces Mineralocorticoids such as aldosterone 2 Zona Fasiculata is the middle layer and produces Glucocorticoids such as hydrocortisone and cortisol 3 Zona Reticularis is the deepest layer and produces Gonadocorticoids 2 The Endocrine Gonads a Testes 1 Within the ct surrounding the seminiferous tubules are small clusters of epithelial endocrine cells called the Interstitial Cells of Leydig a These cells produce the male sex hormone testosterone b Ovaries 1 The ovary produces the female sex hormone estrogen a Estrogen allows for the maintenance of secondary female sexual characteristics and helps to regulate the reproductive cycle 2 The ovary will also produce the female sex hormone progesterone a The function for progesterone is known only for mammals 1 It plays a role in ovulation and in maintaining the endometrial thickening for implantation of the embryo C Endocrine Organs That Are Derived From Endoderm 1 The Thyroid a The thyroid develops from epithelial cells located on the floor of the pharynx 1 Initially the thyroid was just a few scattered cells that could accumulate iodine and produce Thyroxine 2 Its degree of organization today varies among the vertebrates a In some teleosts it is composed of only a few clusters of cells along the ventral aorta on the pharyngeal floor b In most tetrapods it arises as a median evagination of the floor of the second pharyngeal pouch 1 It will develop into a paired gland in placental and marsupial mammals 2 In other tetrapods such as monotremes turtles snakes and a few bird species it is a singular structure often called a median thyroid b In all vertebrates the thyroid produces thyroxine 1 Thyroxine is produced by the Follicular Cells a Follicular cells are arranged into hollow spheres called follicles 2 Thyroxine is dumped into the lumen of the follicle where it is stored until needed as a colloidal mass called Thyroglobulin a The release of thyroxine is controlled by a secretion of the anterior pituitary called TSH c Mammals also produce another hormone called Calcitonin 1 Calcitonin is produced by Parafollicular Cells a Parafollicular cells are arranged into small clusters between the follicles 1 Parafollicluar cells migrate into the thyroid from the developing ultimobranchial glands b Calcitonin regulates bloodcalcium levels 1 It causes an increase in the storage of calcium when bloodcalcium levels are high 2 The Parathyroids a Parathyroids also arise as evaginations of the pharyngeal floor 1 In most vertebrates that possess the parathyroids the parathyroids are located either within the thyroid or very close to the thyroid 2 The number of parathyroids present vary between species a Humans have four two pairs on the posterior surface of the thyroid b Crocodilians have two parathyroids one pair c Some reptiles have six parathyroids arranged into three pairs b The parathyroids produce Parathyroid Hormone PTH which helps to regulate bloodcalcium levels 1 PTH causes calcium to be removed from bone tissue when bloodcalcium levels are too low 3 The Ultimobranchial Glands a Ultimobranchial glands develop from the last pair of pharyngeal pouches 1 These glands produce calcitonin b Ultimobranchial glands are present in all gnathostomes excepting mammals 1 Mammalian ultimobranchial glands migrate into the thyroid and become the parafollicular cells 4 The Thymus a The thymus is a lymphoid organ that in birds and mammals will also have an endocrine role 1 The thymus in mammals and birds produces the hormone Thymosin that serves to stimulate the immune response b The thymus is basically a ct capsule filled with lymphocytes and macrophages 1 Its main lymphoid role is to serve as the site of T cell maturation a As T cell production decreases the parenchyma of the thymus is progressively replaced by adipose and the organ degenerates c In many young birds an evagination of the cloaca forms the Bursa of Fabricus and supplements the thymus in the immune system 1 However it is not known to produce thymosin 5 The Pancreas a The pancreas serves both an exocrine and an endocrine role b The pancreas arises as an endodermal evagination of the foregut 1 It is a ct capsule filled with secretory epithelial cells arranged into lobes and lobules a Most of the secretory cells are exocrine and produce a variety of substances that aid in digestion 1 These cells are called Acinar Cells collectively and their product is collectively known as Pancreatic Juice b Among the exocrine cells are clusters of endocrine cells 1 The nature of the relationship between exocrine and endocrine cells varies among the vertebrates a In agnathans the two cell populations are located so far apart as to allow for no true pancreas b In many jawed fishes the two components are more or less separate c In mammals we see the endocrine pancreas arranged as small clusters of cells amid the exocrine pancreas called Isles of Langerhans or Pancreatic lsles c As is the case with most endocrine organs the endocrine pancreas secretes its products into fenestrated capillaries d The endocrine pancreas in most vertebrates produces the hormones insulin and glucagons which both regulate bloodglucose levels 1 lnsulin causes glucose to be stored as glycogen when bloodglucose levels are high 2 Glucagon causes glucose to be released from glycogen into the blood when bloodglucose levels are low 3 Note insulin and glucagons are most likely the phylogenetically oldest of the hormones D The Diffuse Endocrine System 1 Along with discrete endocrine organs the endocrine system also consists of numerous unicellular endocrine glands distributed throughout the body a Ex the enteroendocrine cells of the digestive tube secrete a variety of hormones that play a role in digestive physiology b We have seen how cellular aggregates can develop into discrete organs over evolutionary time Histology Terms Tissue group of closely related cells similar in structure and perform similar functions 4 classes Epithelial Connective Muscle Nervous Extracellualar Matrix acelluar matter in tissue Epithelial Tissue covers all body cavities inner and outer Cells are very close to each other intercellular junctions Desmosomes cellular junctions which bind cells together membranes not fused Tight Junction binds cells together cell membranes fuse Gap Junction allows communication between cells ion channels Basement Membrane separates epithelium from underlying tissue acellular made of Epithelium underlying connective tissue Allows for regeneration support defense Squamous cells low attened cells scale like Cuboidal Cells cube shaped equal height and width Columnar Cells column shaped taller then wide Simple 1 cell layer Strati ed 1 cell layer Pseudostrati ed composed of 1 layer of unequal height Simple Squamous 1 layer of attened cells blood vessels alveoli lymphatic M esothelium epithelium lining the ventral body cavities Endothelium epithelium lining all the hollow organs of circulatory system Simple Cuboidal single layer of cube shaped cells small glands ovary surface Simple Columnar single layer of column shaped cells alimentary canalgastrointe stinal Can have cilia on the apical surface simple ciliated columnar epithelium Pseudostrati ed Columnar single layer of columnar shaped cells w varying height Upper Respiratory Tract Strati ed Squamous more than one layer of attened cells skin vagina mouth Found in areas of much abrasion 2 types Stratified Squamous Keratinized Skin Stratified Squamous NonKeratinized esophagus Strati ed Cuboidal 23 layers of cube shaped cells rare mammary gland Strati ed Columnar 23 layers of column shaped cells rare Transitional stratified epithelium of variably shaped cells Allows for some stretching Glandsepithelial cells that secrete an aqueous uid product Unicellular Glands 1 cell Multicellular Glands 1 cell Exocrine Glands secrete product into ducts multiunicellular Endocrine Glands don t secrete product into ducts released into blood stream Multiunicellular secrete hormones Connective Tissue very diverse 4 classes connective tissue proper blood bone amp cartilage Have an extensive extracellular matrix which separates them All from mesenchyme stem cells Connective Tissue Proper 2 types Loose amp dense Loose Connective Tissue Areolar Connective Tissue underlies most of body epithelia surrounds small nerves and blood vessels Matrix all three types of bers collagen reticular elastic Collagenstrongest most abundant lots of tension Reticular branches more exible than collagen Elastic weakest most exible use protein called elastin Cell Typeslots of different cells found in Areolar Tissue F 139 broblastsimmature CT cells produces the bers F 139 brocytemature cell inactive Macrophages White Blood Cells Mast Cells Fight in ammation Plasma Cells secretes lymphocytes Reticular Connective Tissue only has reticular ber found in areas where Some strength stretching is needed AdiposeFat Tissue stores nutrients insulates body protects from trauma Adipocytes Dense Connective Tissue much higher ber content lower cell content much stronger Dense Irregular Tissue primarily collagen running in random pattern Found in dermis Dense Regular Connective Tissue collagen running in repetition patterns Collagen runs parallel to each other Very Strong in 1 direction ligaments tendons Elastic Connective Tissue uses just elastic bers areas that need exibility Blood Plamaextracellular matrix very uid Has 3 types of cells whiteampred blood cells and platelets Transport materials throughout body defends body Cartilage Found in embryonic skeleton replaced by bone later some will remain Lays framework for areas of body needing support ears nose Main cell Chondrocyte Chondrocyte comes from chondroblasts secretes ec matrix Lacunae chondrocyte home inside matrix 3 Types Hyaline Elastic Fibrocartilage Bone Densest has minerals in ec matrix Main Cell Osteocyte Osteocyte comes from osteoblast secretes ec matrix Lacunae Osteocyte home in matrixb Muscle Tissue allows movement of the body Uses myo bers which contract only Actin and Myosin 3 Types Skeletal Cardiac Smooth Skeletal striated multinucleated voluntary Cardiacheart onlystriated 12 nuclei involuntary branching Smoothmonstriated 1 nuclei involuntary Nervous Tissue regulates amp controls body functions 2 Cell Types Neurons amp Supporting Cells Neuronsconduct information Supporting Cells assist neurons Makes up nerves spinal cord brain Notes All epithelium has underlying loose connective tissue Epithelium lacks blood vessels needs connective tissue for vascularization Connective tissue has little regeneration and decreases with age Muscle and Nerve cells can not be regenerated after birth Blast immature cell produces part of matrix in a tissue


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