Principles of Biology II
Principles of Biology II BIOL 112
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Chapter 42 CIRCULATION AND GAS EXCHANGE Organisms must exchange materials and energy with its environment and this exchange ultimately occurs at the cellular level Cells live in aqueous surroundings The materials they need must move across the plasma membrane into the cytoplasm and metabolic wastes must move out CIRCULATORY SYSTEMS REFLECT PHYLOGENY Internal transport and gas exchange are functionally related in most animals Diffusion is not enough for transporting substances over long distances more than a few millimieters in animals The time it takes to diffuse a substance is a function of the square of the distance The same amount will take 1 sec to diffuse lum 100 sec for 1 mm 3 hours for 1 cm INVERTEBRATES In all animals uid between the cells called interstitial uid or tissue uid bathes the cells and provides a medium for diffusion of oxygen and nutrients Sponges cnidarians ctenophorans platyhelminthes etc depend on diffusion for internal transport The gastrovascular cavity serves for both digestion and distribution of substances throughout the body Triploblastic animals with more complex body plan use open and closed circulatory systems Both systems have a circulatory uid blood a set of tubes blood vessels and a pump heart Heart creates blood pressure that acts as the motive force to move the uid through the set of tubes Arthropods and mollusks have an open circulatory system Blood ows into a hemocoel bathing the tissues directly The hemocoel is made of spaces or sinuses that surround the organs The hemocoel is not part ofthe coelom Hemolymph blood and interstitial uid are indistinguishable When the heart contracts hemolymph is pushed out of the tubes into the sinuses when the heart relaxes hemolymph is pulled into the tubes through openings called 0stia o Hemocyanin an oxygentransporting pigment found in some mollusks and arthropods contains copper Some invertebrates e g cephalopods echinoderms annelids and vertebrates have a closed circulatory system 0 Blood is con ned to the vessels 0 Blood is different from the interstitial uid 0 Chemical exchange occurs between the blood and interstitial uid Nemerteans have a primitive circulatory system that is closed but does not have a pumping organ Blood moves depending on the movements of the animal and contractions in the wall ofthe large blood vessels VERTEBRATES Functions of the vertebrate circulatory system Transports oxygen metabolic wastes nutrients and hormones Helps maintain uid balance Defends the body against invading microorganisms Distributes metabolic heat to maintain normal body temperature Helps maintain appropriate pH 959 Exchange of materials occurs through the thin wall of capillaries The human circulatory system is also known as the cardiovascular system Circulatory systems consists of 1 Blood a connective tissue made of cells cell fragments and a uid known as plasma 2 The heart consists of one or two atria which receive the blood and one or two ventricles which pump the blood 3 A system of blood vessels or spaces through which the blood circulates arteries veins and capillaries forming networks or capillary beds 1 In sh there is one atrium and one ventricle and blood ows in a single circuit Atrium gt ventricle gt aorta gt gill capillaries gt organ capillaries gt atrium 0 Blood must pass through two capillary beds in each circuit Blood pressure drops substantially and oxygenrich blood ows slowly through the system 2 In amphibians there are two atria and one ventricle 0 Systemic and pulmonary circulation a double circuit Ventricle gt aorta gt body capillaries gt veins gt right atrium gt ventricle gt pulmonary artery gt lung and skin capillaries pulmocutaneous gt veins gt left atrium gt ventricle o Oxygenpoor blood is pumped out the ventricle before the oxygenrich blood enters it 3 Reptiles have a double circuit blood ow and the ventricle is partly divided 0 Some mixing ofblood occurs 0 Ventricle sides contract at different times oxygenrich blood is diverted to the systemic ow and oxygenpoor blood is diverted to the pulmocutaneous circulation o Crocodiles have two ventricles 4 In crocodilians birds and mammals the heart ventricles are separated There are two ventricles Body capillaries gt veins gt right atrium gt right ventricle gt pulmonary arteries gt lung capillaries gt pulmonary veins gt left atrium gt left ventricle gt aorta gt body organs gt veins gt right atrium o The left side ofthe heart receives and pumps oxygenrich blood the left side ofthe heart receives and pumps oxygenpoor blood 0 Endotherms consume more energy than ectotherms and circulatory system must deliver about 10 times more oxygen and fuel to their tissues than ectotherms of equal size Mammalian Circulation The Pathway Double Circulation In Mammals Systemic circulation delivers blood to the tissues Coronary arteries feed the heart Carotid arteries bring blood to the brain Subclavian arteries to the shoulder region and arms Mesenteric arteries to the intestines Renal arteries to the kidneys Iliac arteries to the legs Four arteries deliver blood to the brain two carotids and two vertebral arteries Blood returns to the heart in veins The superior vena cava collects blood from jugular and subclavian veins drain the brain and arms Renal iliac and hepatic veins empty into the inferior vena cava Coronary capillaries empty in the coronary veins which in turn join to form a large vein the coronary sinus that empties directly into the right atrium The hepatic portal system delivers nutrients to the liver The hepatic portal system delivers blood rich in nutrients to the liver Blood ows from the liver to the small intestine through the superior mesenteric altery Blood ows through the capillaries of the intestine and collect glucose amino acids and other nutrients This blood passes to the mesenteric vein and then into the hepatic portal vein which delivers the nutrient rich blood to the liver Mammalian Heart A sac of connective tissue the pericardium protects human heart The inner surface of the pericardium and outer surface of the heart are covered by a smooth layer of endothelium The space in between the pericardial cavity is lled with a uid which reduces friction during heartbeats The heart consists of two atria which receive the blood and two ventricles which pump the blood On the upper surface of each atria lies a small muscular pouch called the auricle l The right atrio ventricular valve AV or tricuspid valve controls the blood ow between the right atrium and right ventricle 2 The left AV is called the mitral valve 3 The cordae tendinae attach the valves to the papillary muscles of the heart 4 The semilunar valves guard the exits from the heart aortic and pulmonary valves When the heart contracts it pumps blood when it relaxes is lls with blood One complete sequence of pumping and lling is called the cardiac cycle The contraction of the heart is called systole and the relaxation of the heart is known as diastole When the semilunar valves do not close tightly during diastole the blood ows back with a hiss known as a heart murmur Cardiac output is the volume of blood pumped by the left ventricle into the aorta in one minute The stroke volume is the volume of blood pumped into the aorta during one beat mlstroke o The average stroke volume is 75ml Heart rate is the number of contractions per minute strokesmin 0 Cardiac output stroke volume X heart rate mlmin Pulse is the rhythmic stretching of the arteries caused by the blood pressure due to the contraction of the ventricles The electrical activity of the heart spreads through the body uids to the body surface and can be recorded in a graph called the electrocardiogram ECG or EKG The oscilloscope and the electrocardiograph are the instruments used to record and monitor the heart activity A heart murmur is a hissing sound caused by a defect in one of the valves A stream of blood squirts back through the valve Heartbeat The heart is capable of beating independently of the nervous system It is called a myogenic heart Most arthropod hearts beat under the control of the motor nerves outside of the heart they are called neurogenic hearts At the end of cardiac muscle cells there are dense bands called intercalated discs gap junctions in which two cells are connected through pores pomtwhere the supenorvena cava enters the hght amum CardAa musele eells branch andmterconnectvxaxntercalatedducs them contract m umsoh nude loeated m the wall between the hght athum and the nght venmcle on the lower part ofthe septum The AV the venmcularwall Purkinie bers Check the followmg sites about the PurkJnJE bers ht eh Wm edAaor NahBundle of Hts htm www med mu eduhxstol argead asob acts642 htm 22 html Endocamlum Structure of O r ff veins and v 39 O Y 3 839 Veins carry blood to the hea1t EB Capillari tissues Smaller secondary branches of arten39es are called arterioles which they carry blood and not by the characteristics of the blood Veins and arteries have three layers of tissues 0 Tunica intima consists of squamous epithelium endothelium o Tunica media is made of connective tissue and smooth muscle 0 Tunica adventitia consists of connective tissue rich in elastic and collagen bers The smooth muscle in the wall of arteries can constrict vasoconstriction or dilate vasodilation The thick wall of the arteries and veins prevent gases from passing through Capillaries form a network between arterioles and venules Precapillary sphincters are located whenever a capillary branches off a metarteriole These sphincters open and close continuously to direct blood to needed sectors of the tissues Vasoconstriction and vasodilation help maintain the appropriate blood pressure and control the volume of blood passing to a particular tissue Changes in blood ow are regulated by the autonomic nervous system in response to metabolic needs of tissues Blood ow Blood ow follows the law of continuity o If a pipe39s diameter changes over its length a uid will ow through narrower segments of the pipe faster than it ows through wider segments 0 The volume of ow per second must be constant through the entire pipe Blood ows faster in the aorta than in a capillary The total cross sectional area of the capillaries determines the rate of ow The number of capillaries is so great that the total crosssectional area is much greater in capillary beds than in any other part of the circulatory system Capillaries are the only vessels with walls thin enough to permit the transfer of substances between the blood and interstitial uid The slow blood ow enhances the exchange Blood pressure Fluids ow from the area of greater pressure to the area of lower pressure Blood pressure is the hydrostatic pressure the blood exerts against the wall of the vessel and that propels the blood Blood pressure is greater in arteries than in veins When the heart contracts the blood pressure is the highest in the arteries systolic pressure Resistance is the opposition to ow It depends on 0 Blood viscosity the greater the viscosity the greater the resistance 0 Total blood vessel length the longer the vessel the longer the resistance 0 Blood vessel diameter the smaller the vessel the greater the resistance Peripheral resistance refers to the friction the blood encounters when it ows through the circulatory system As the elastic arteries return to their more relaxed condition during diastole the pressure in the circulatory system is maintained This is called the diastolic pressure m diastolic pressure diastole relaxation of the heart muscles 80 systolic pressure systole contraction of the heart muscles Nerve impulses and hormones control the arteriole muscles and vasodilation or vasoconstriction Cardiac output is adjusted in concert with changes in peripheral resistance This coordination maintains a constant blood ow Blood ow through capillaries Capillaries in the brain heart liver and kidneys are usually lled to capacity Nerve impulses and hormones control the contraction mechanism of the smooth muscles of arterioles and precapillary sphincters and the distribution of blood in the capillary beds 0 After a meal blood is diverted to the digestive track 0 During strenuous exercise blood ow to the muscles increases Capillary exchange All exchange of substances takes place across the thin endothelial wall of the capillary Some material may be transported across the wall cell by endocytosis and then released at the other end by exocytosis Small molecules like oxygen and carbon dioxide diffuse down the concentration gradient Diffusion also occurs through intercellular spaces Capillary pressure pushes out uid with sugars salts oxygen and urea into the interstitial uid Blood cells and blood proteins are too large to pass through the endothelium causing an increase in solute concentration osmolarity Water is recuperated downstream near the venule end of the capillary About 85 of the uid is recuperated that way The remaining 15 is returned to the blood stream by the lymphatic system LYMPHATIC SYSTEM The lymphatic system is an accessory circulatory system which 1 Collects and returns interstitial uid to the blood 2 Defends against diseasecausing organisms 3 Absorb lipids from the small intestine The lymphatic system consists of o Lymphatic vessels that conduct lymph o Lymphatic tissue organized into lymph nodes and nodules o Tonsils thymus gland and spleen Interstitial uid enters the lymph capillaries and is called lymph Lymph capillaries are deadend and extend into almost all tissues of the body Lymph capillaries join to form large lymphatics lymph veins 0 Thoracic duct empties the lymph into the left subclavian vein 0 Right lymphatic duct empties into the right subclavian vein Valves within the lymph veins prevent the lymph from owing backwards When blood enters the capillaries under pressure some plasma and proteins filters out into the tissues forming the interstitial uid Only about one fourth of the blood proteins pass into the tissues Lymph capillaries are made of overlapping cells that separate under pressure allowing excess interstitial uid and proteins in it to enter and drain the tissue Obstruction of the lymph vessels causes edema the swelling that occurs due to the accumulation of interstitial uid BLOOD In invertebrates with an open circulatory system blood is no different from interstitial uid the hemolymph Animals with a closed circulatory system have blood which is different from the interstitial uid Plasma Blood is a type of connective tissue containing different kinds of cells suspended in a liquid matrix the plasma Plasma makes about 55 ofthe blood The remaining 45 are made up of blood cells and platelets Plasma is about 92 water 7 proteins and the rest consists of nutrients organic wastes and electrolytes ions Blood makes up about 8 ofthe body weight Humans have 4 to 6 liters of blood The plasma contains ions nutrients wastes hormones and respiratory gases The plasma and interstitial uid are similar in composition except that the plasma contains a higher protein concentration than the interstitial uid When proteins involved in blood clotting have been removed from the blood the remaining liquid is called serum Ions in the plasma help maintain the osmotic balance on the blood and contribute to buffer the blood that usually has a pH of 74 in humans Plasma proteins act as buffers in order to maintain a constant pH of 74 Globulins are of three kinds HDL highdensity lipoproteins transport fats and cholesterol Some globulins are lipoproteins that bind to minerals vitamins lipids and cholesterol to dissolve and transport Other globulins are antibodies that provide immunity against certain diseases Globulins make up 33 of the plasma proteins Albumins help to regulate the amount of uid in the plasma and interstitial uid and help maintain osmotic pressure and proper blood volume They constitute 60 of plasma proteins Fibrinogen and prothrombin function in the clotting reaction 0 When proteins involved in blood clotting have been removed from the blood the remaining liquid is called serum Blood cells Red blood or erythrocytes cells RBC transport oxygen and carbon dioxide Made in the bone marrow ribs long bones vertebrae and skull bones 54 million ul mm3 in men and 50 million ul mm3 in women Lack nucleus and mitochondria and live for about 120 days Liver and spleen remove old RBC from circulation Hemoglobin is the oxygen transporting protein contains Fe Hemoglobin binds to Oz and NO nitric oxide NO relaxes the walls of the capillaries and helps in the diffusion of oxygen White blood cells or leukocytes WBC defend the body against diseasecausing microorganisms About 7000 cellsul mm3 in human blood 5000 10000 cells on the average The number increases temporarily during infections Made in the bone marrow Travel in the blood stream for a short time and can migrate across the endothelial lining of the capillaries Their collective function is to fight infections Platelets or thrombocytes function in blood clotting They are pinched off from very large cells called megakaryocytes in the red bone marrow Cell fragments containing enzymes they are 2 to 3 pm Lack nucleus About 300000 plateletspl Stem cells and the replacement of cellular elements Cellular elements erythrocytes leukocytes and platelets Cellular elements wear out and are replaced constantly throughout the person s life Phagocytes in the spleen and liver destroy red blood cells Their chemicals are recycled into new cellular material Erythrocytes leukocytes and platelets develop from a population of cells called pluripotent stem cells found in the red bone marrow of long bones ribs vertebrae breastbone and pelvis Pluripotent cells have the potential to differentiate into any kind of cells or into cells that produce platelets The population of stem cells renews itself while replenishing the cellular elements RBCs are produced via a negative feedback mechanism When the oxygen reaching the tissues is low the kidney converts a plasma protein to a hormone called erythropoietin which stimulates production of erythrocytes Blood clotting Coagulation Fibrinogen and prothrombin are proteins found in the plasma Platelets release several factors that combine with Ca2 in order to convert prothrombin to the active enzyme thrombin Thrombin then converts the soluble protein fibrinogen into the insoluble fibrin Fibrin polymerizes and sticks to the damaged surface forming a web RBC and platelets get trapped in the web and form the clot There are more than 30 factors interacting during the clotting process The absence of one of these factors due to genetic mutation is the cause of hemophilia Cardiovascular diseases Diseases of the heart and blood vessels usually result in a heart attack or a stroke Heart attack is the death of heart muscle due to oxygen deprivation Stroke is the death of brain tissue usually caused by the rupture or blockage of an artery Heart attacks and strokes are frequently caused by a clump of platelets and brin blood clot or thrombus that is formed within the blood vessels The traveling clot is called an embolus and can get trapped in an artery that is too narrow for it to pass The artery gets clogged and the blood ow stops to the tissues downstream which become deprived of oxygen and begin to die Atherosclerosis is often the cause of thrombus formation Plaques form when fibrous connective tissue and lipids partially close the lumen of the artery If the plaque becomes hardened with calcium deposits the disease is called arteriosclerosis The rough walls formed by the plaques facilitate the clustering of platelets and the formation ofblood clots Hypertension or high blood pressure promotes atherosclerosis and increases the risk of heart attack and stroke 0 Lowdensity lipoproteins or LDL tend to deposit cholesterol and build plaques in the arteries 0 Highdensity lipoproteins or HDL reduce cholesterol deposition Desirable 7 Less than 200 mgdL Borderline high risk 7 2007239 mgdL High risk 7 240 mgdL and over Your LDL cholesterol level Your LDL cholesterol level greatly affects your risk of heart attack and stroke The lower your LDL cholesterol the lower your risk In fact it s a better gauge of risk than total blood cholesterol Your LDL cholesterol will fall into one of these categories LDL Cholesterol Levels Less than 100 mgdL Optimal 100 to 129 mgdL Near Optimal Above Optimal 130 to 159 mgdL Borderline High 160 to 189 mgdL High 190 mgdL and above Very High http wwwamericanheartorgpresenterjhtmlidentifierl 83 GAS EXCHANGE IN ANIMALS The exchange of gases between an organism and its environment is called respiration Organismic respiration brings oxygen from the environment to the cells 0 Aerobic respiration occurs within the cell in the mitochondria Oxygen is taken in by the organism and carbon dioxide is released into the environment The respiratory medium is the source of oxygen air or water depending on the habitat of the organism Ventilation is the movement of air or water over the respiratory surfaces The tissue where the gas exchange takes place is called the respiratory surface Gas exchange occurs entirely by diffusion The rate of diffusion is proportional to the area of the respiratory surface and inversely proportional to the square of the distance thickness through which the molecules must move Respiratory surfaces are thin and with large areas In order for oxygen and carbon dioxide to diffuse across a cell membrane they must dissolve in water Respiratory surfaces must be maintained moist and air has to pass through a long series of tubes to reach these surfaces Living cells must be bathed is water in order to maintain their plasma membrane TYPES OF RESPIRATORY SURFACES 1 Body surface Used by protists and small animals with low metabolic rate e g sponges cnidarians and atworms 2 Gills containing capillaries Outfoldings of the body surface that are suspended in the water Specialized body appendages drive water over the gill surface increase ventilation Water is more viscous and dense than air and the aquatic animal must spend a lot of its energy moving water over the gills o Aquatic animals spend 20 of its energy while terrestrial animals spend 1 2 of its total energy Echinoderms have dermal gills Chordates usually have internal gills In bony sh the gills are protected by a bony plate the operculum Counter current system is an ef cient method of obtaining oxygen more than 80 of the oxygen in the water can be removed by this method 3 Tracheal system is an adaptation to terrestrial living that delivers oxygen to all parts of the body 0 Air contains much larger concentration of oxygen than water 0 Terrestrial animals have to compensate for water loss during breathing By having the respiratory surface inside the body evaporation is decreased 0 It consists of a network of tracheal tubes or tracheae that deliver air directly to the body cells through the tiny nal branches of the tracheoles o All body cells lie within a very short distance pm of a tracheole o The tracheae open on the body surface through up to 20 tiny openings called spiracles 0 Large insects and ying insects enhance ventilation by using muscles like bellows to pump air into the tracheal tubes 4 Lungs formed by in growth of the body surface or from the wall of the body cavity 0 Lungs are in one location 0 The circulatory system must transport gases from the lungs to other parts of the body Spiders have quotbook lungsquot 0 Located in an inpocketing of the abdominal wall 0 Open to the outside by a spiracle o A series of plates rich in hemolymph separated by air spaces Osteichthyes have a swim bladder o It is used to control buoyancy o Lung shes use it breath air at certain times in their life cycle Amphibians and reptiles have simple lungs o The lungs of toads and frogs are simple sacs with ridges that increase the respiratory surface Some amphibians do not have lungs and exchange gases through the skin Reptiles have sacs with folding of the wall to increase the respiratory surface HUMAN RESPIRATORY SYSTEM The human respiratory system is typical of airbreathing vertebrates Nostrils are the opening of the nose Nasal cavities moisten warm and lter the air Pharynx or throat is used also by the digestive system Larynx also called quotvoice boxquot contains the vocal cords and is supported by a cartilage Epiglottis is a small ap of tissue that closes the larynx during swallowing Trachea or windpipe is supported by rings of cartilage Bronchi are branches of the trachea that lead to each lung 0 Both trachea and bronchi are lined with a mucous membrane containing ciliated cells 0 Mucus traps dust pollen bacteria and other particles Alveoli are tiny air sacs at the end of the bronchioles and are lined with a very thin epithelium Capillaries surround the alveoli Gas exchange occurs in the alveoli of the lungs The lungs as such consist mostly of air tubes and elastic tissue with a very large internal surface Bronchioles and alveoli make most the lungs Each lung is covered with a pleural membrane which also lines the thoracic cavity Pleural cavity is the space in between the pleural membranes and it is lled with a uid 0 The pleural uid provides lubrication between the lungs and the body wall Passage of air Nostrils a nasal cavities a pharynx a larynx a trachea a bronchi bronchioles a alveoli BREATHING Ventilation is accomplished by breathing Breathing is the mechanical processes of moving air from his environment into the lungs inspiration and expelling the air from the lungs expiration Amphibians like frogs ventilate their lungs by positive pressure 0 The lowering of the buccal cavity draws air through the nostrils into the mouth With the nostrils and mouth closed the frog raises the oor of the oral cavity and air is forced down the trachea Compression of the body wall and elastic recoil of the lungs force air back out of the lungs during exhalation Mammals ventilate by negative pressure During inspiration the volume of the thoracic cavity is increased by contraction of the diaphragm Contraction moves the diaphragm downward increasing the volume of the thoracic cavity The pressure of the air in the lungs decreases by 2 or 3 mm Hg below the atmospheric pressure With the increase in volume in the thoracic cavity the pressure drops and air is forced in by the atmospheric pressure Expiration occurs when the diaphragm relaxes and moves up Diaphragm and rib muscles account for shallow breathing During vigorous exercise other muscles of the neck back and chest further increase ventilation volume by raising the rib cage even more The normal amount of air inhaled at rest is called tidal volume N 500 ml The vital capacity is the maximum amount of air a person can exhale after filling the lungs to the maximum extent It brings about 34 liters for college females and 48 liters for males After forcefully exhaling the alveoli remain in ated with the residual volume of air that cannot be expelled Birds have the most efficient respiratory system of any living vertebrate Their lungs have air sac extensions that reach into many parts of the bird39s body BREATHING CONTROL CENTERS Breathing is regulated by respiratory centers in the pons medulla oblongata and in the walls of the carotid arteries and aorta Neurons originating in the medulla send messages to the diaphragm and external intercostal muscles causing them to contract and inspiration occurs Negative feedback mechanism prevents our lungs from overexpanding stretch sensors in the lung tissue send nerve impulses back to the medulla inhibiting its breathing control center After several seconds the neurons become inactive the muscles relax and expiration occurs Chemoreceptors sensitive to increases in CO and H and to low 02 concentrations regulate the respiratory centers The medulla control center maintains homeostasis by monitoring the amount of CO in the blood Slight drop in the pH of the blood and cerebrospinal uid means an increase in CO in the tissues and blood The medulla registers these changes and increases the depth and rates of breathing so the excess of C02 is eliminated in exhaled air Oxygen concentration generally does not play an important role in breathing regulation Only if the partial pressure of oxygen drops markedly the aortic and carotid centers become stimulated to send messages to the respiratory centers in the brain and breathing increases PRESSURE GRADIENT AND THE DIFFUSION OF GASES Oxygen transport The difference in partial pressure of oxygen between the inhaled air and the blood allows the oxygen to diffuse Oxygen makes 21 by volume of the atmosphere The atmosphere exerts a pressure of 760 mm Hg at sea level The partial pressure of oxygen is 760 mm Hg x 021 160 mm Hg Fox 160 mm in air and Fox 40 mm in venous blood Therefore oxygen diffuses into the blood Fox 100 mm in arterial blood P0X 0 40 mm in tissues Therefore oxygen diffuses into the tissues Fick39slzw the greater the pamal pressure dAfference andthe 1argerthe surface area the fasterthe gas wru dAffuse Respiratnry pigments gas transpnrt and bland hunering resprratory prgrnents Hernnglnhin rnereases the eapaerty to transport oxygen by about75 tunes There are seyera1 types ofhemoglobm or re1eases rt the other three follow qurexdy All eontarn rron as part of a herne group Herne group rs bound to a protern eaned globm Protern poruon yanes m srze and AAm dAfferent speeres w m V d HEMOGLOBIN M F 4sz qubiw Lack herne group Copperrcon ammg proterns Drssolyedrn the bloodratherthan eontarnedrn eeu Blue when eornbrned wrth oxygen wrthout oxygen rs eo1or1ess Itrs found rnany speeres ofmollusks and arthropods 0 About 200 ml of 02 per liter ofblood in mammals The maximum amount of oxygen that can be transported by hemoglobin is called the oxygen carrying capacity The actual amount of oxygen bound to hemoglobin is the oxygen content The ratio of oxygen content to oxygen capacity is the percent oxygen saturation The conformation of the hemoglobin protein is sensitive to pH The affinity of hemoglobin for oxygen decreases Oxyhemoglobin dissociates faster in an acid medium Bohr Effect Bohr Shift Changing the blood pH affects the of 02 saturation of blood Carbon dioxide reacts with water to form carbonic acid An active tissue will lower the pH of its surroundings and cause hemoglobin to release more oxygen Carbon dioxide transport Carbon dioxide is transported mainly as bicarbonate ions About 70 of the C02 dissolves in the plasma and forms HC0339 and H lowering the pH About 7 10 dissolves in the plasma About 20 23 enter the red blood cells and combines with hemoglobin forming carbaminohemoglobin This reaction occurs in the RBC catalyzed by carbonic anhydrase Carbonic anhydrase 02 H20 gt H2C03 H HH HC037 Most of the H released from carbonic acid combine with hemoglobin and do not change the pH ofthe blood Many of the bicarbonate ions leave the RBCs and diffuse into the plasma As C02 diffuses out of the alveolar capillaries the resulting lower C02 concentration reverses the previous reaction Deep diving Diving mammals have high concentration of myoglobin an oxygen binding pigment found in muscles Myoglobin stores oxygen in diving mammals up to ten times more than in terrestrial mammals Weddell seal store about 25 of its oxygen in muscle compared to only 13 in humans Dive down to 500 meters and remain underwater for about 20 minutes sometimes for more than one hour After 20 minutes the supply of oxygen in myoglobin is used up and ATP is derived from fermentation Elephant seal dive to depth of 1500 m almost 1 mile and remain submerged for two hours Diving re ex reduces the heart rate blood is redistributed and other physiological changes occur that allow the diving mammal to conserve oxygen Scholarships httpwww house oVrovbalquotWW 2006 39 39 quot Directorvpdf Spring Final Exam Schedule httpwww 0111 Hill A J I I cu Snrinowm pxame html Chapter 29 PLANT DIVERSITY I HOW PLANTS COLONIZED LAND There are about 290000 of land plants on Earth LAND PLANTS EVOLVED FROM GREEN ALGAE Charophycean ancestor Charophyceans are the green algae most closely related to land plants Land plants probably are probably derived from a group of green algae called charophytes Land plants share with the charophyceans the following traits 1 Rosette cellulosesynthesizing complexes land plants and charophyceans posses a rosetteshape array of proteins that synthesize cellulose microfibrils in their cell wall Other cellulose wallcontaining algae e g brown algae dinoflagellates have linear arrays of celluloseproducing proteins This suggests a common ancestor between the charophytes and land plants This rosette synthesizing system evolved independently of the cellulose making system of other green algae 2 Peroxisomes enzymes the charophyceans and land plants have enzymes in their peroxisomes that minimize the loss of carbohydrate due to photorespiration Other alga groups do not have these enzymes in their peroxisomes 3 Structure of the flagellate sperm details of the sperm of charophyceans resemble those of land plants that have flagellated sperms P Cell plate formation during cytokinesis cell division features a complex network of microtubules and Golgi vesicles the phragmoplast again as found in all land plants 5 DNA and RNA sequences support their close relation to the charophytes especially Chara and Coleochaete TERRESTRIAL ADAPTATION OF LAND PLANTS ADAPTATIONS ENABLING THE MOVE TO LAND A layer of sporopollenin protects charophytes from desiccation sporopollenin is found in the spore wall of land plants Danger of desiccation required new adaptations transport tissue cuticle etc Support against gravity Plants are eukaryotic multicellular mostly autotrophic organisms with haploiddiploid life cycles which retain embryo within female sex organ on parent plant the cell wall contains cellulose Scientists are studying the ultrastructure of cells analyzing macromolecules and comparing morphology with life cycles There are several proposals to rearrange the boundaries of the kingdom Plantae 0 Only the Embryophytes the present and traditional system 0 Expand it to include the charophyceans Kingdom Streptophyta 0 Expand it further to include all the green algae Chlorophyta Kingdom Viridiplantae DERIVED TRAITS OF PLANTS The following characteristics are common to all four groups of land plants but are absent in the charophyceans 1 Apical meristem cluster of embryonic cells found at the tip of shoots and roots 2 Alternation of generations a characteristic life cycle Alternation of generation does not occur in the charophyceans This suggests that alternation of generation arose independently in land plants A life cycle characterized by a multicellular haploid gametophyte stage followed by a multicellular diploid sporophyte stage Multicellular dependent embryos The zygote is retained surrounded by tissues of the gametophyte The parental tissue provides the embryo with nutrients Placental transfer cells present in the embryo and sometimes in the gametophyte as well enhance the transfer of nutrients 3 Spores produced in sporangia haploid reproductive cells that become a multicellular haploid gametophyte by mitosis The multicellular sporangium contains sporocytes the cells that undergo meiosis to form spores Sporopollenin the most durable organic material known makes the walls of the spores P Multicellular gametangia the gametes of land plants are produced in multicellular organs called gametangia Algae produce their gametes in unicellular gametangia inside a single cell Adaptations for water transport and conservation 1 Waxy cuticle to protect against desiccation 2 Stomata sing stoma for gas exchange and control of transpiration 3 Transport system or vascular tissue Secondary metabolic compounds Land plants make many metabolic compounds that are produced by side branches off the primary metabolic pathways that make lipids carbohydrates proteins and other compounds common to all organisms Cell wall contains lignin a polymer to strengthen and support upright structures Other secondary compounds are alkaloids tannins and phenolics flavonoids These compounds functions as a protection against herbivores absorb harmful UV radiation and are involved in the symbiotic relationship with soil microbes ORIGIN OF LAND PLANTS About 475 million years ago in the midOrdovician plants were widespread all over the world as shown by the many spores found in sediments of this period In a relatively short time of about 50 million years plant diversified abundantly and colonized many land areas There are four main groups of land plants Bryophytes including mosses Pteridophytes including ferns and seedless vascular plants Gymnosperms including conifers O O O o Angiosperms including flowering plants Land plants are distinguished from algae by the production of multicellular embryos that remain attached to the mother plant which protects and nourishes the embryos Bryophytes are distinguished from the other three groups of land plants by the lack of a vascular tissue made of special cells called xylem and phloem Some bryophytes have water and nutrient transport system made of a different kind of cells 0 The vascular system transports water and nutrients Pteridophytes do not produce seeds Gymnosperms and angiosperms produce seeds A seed consists of a plant embryo with a food storing tissue and a surrounding coat for protection 0 The first vascular plants to produce seeds evolved about 360 million years ago 0 Their seeds were not enclosed in any specialized chamber Angiosperms produce flowers and conifers produce quotconesquot a specialized reproductive structure 0 Angiosperms produce their seeds in specialized chambers called ovaries o Gymnosperms do not produce seed in ovaries The word grade is used to designate a collection of organisms that shate a common level of biologial organization or adaptation BRYOPHYTES About 17000 species worldwide divided into three Divisions or phyla Bryophyta the mosses Hepatophyta the liverworts and Anthocerophyta the hornworts Their life cycle is similar but the three groups may not be closely related The bryophytes may form a polyphyletic group Bryophyta refers to the phylum of mosses only bryophytes refer to the three phyla mentioned above Characteristics of the bryophytes 1 Small plants found in moist environments lack woody tissue and usually form mats spread over the ground l Gametophyte generation is dominant sporophyte is parasitic on the gametophyte 3 Bryophytes have cuticle stomata and multicellular gametangia that allow them to survive on land 4 Bryophytes need water to reproduce and most species lack vasculartissue xylem and phloem 5 Water transport is mostly through capillary action diffusion and cytoplasmic streaming They lack true roots stems and leaves The gametophyte of mosses is a onecellthick filament known as the protonema that eventually produces buds having meristematic tissue These meristems produce an upright structure called the gametophore These gametophytes are one to a few cells thick and obtain nutrients and water by direct absorption from the environment Most mosses do not have conducting tissue Some species have specialized cells that conduct water and nutrients but lack lignin in their cell walls The gametophores are anchored by fragile rhizoids Rhizoids are either single elongated cells as those found in liverworts and hornworts or filaments of cells as those of mosses Rhizoids are not made of tissues and do not absorb any significant amount of water In that way they differ from roots Bryophytes have smallest and simplest sporophyte of any group The sporophyte remains attached to the gametophyte throughout its lifetime dependent of the gametophyte for food water and minerals The mature sporophyte of mosses consists of a foot embedded in the archegonium a seta or stalk is present in the phylum Bryophyta and a capsule or sporangium The cap or calyptra closes the peristome or opening or the capsule THE ORIGIN OF VASCULAR PLANTS Ferns and other seedless vascular plants formed the first forests 1 The next step in land plant evolution included the development of an independent sporophyte 0 At first this sporophyte was of equal size as the gametophyte o Cooksonia caledonica from the Silurian 420 million years ago rocks of Europe and North America is the oldest known land plant 0 Small leafless rootless dichotomous axes with terminal sporangia 2 Transport in xylem and phloem o Phloem for the transport of dissolved carbohydrates 0 Xylem for water and mineral transport 0 Lignin strengthens the vascular tissue cells 9 Evolution of roots 0 Roots anchor plants and allow the absorption of water and nutrients from the soil 0 Root tissues of living plants closely resemble stem tissues of early vascular plants preserved in fossils 0 Roots may have evolved from the lowest subterranean parts of the stem 0 The oldest lycophyte fossil had simple roots 400 million years ago 4 From an evolutionary perspective there are two kinds of leaves 0 Microphylls are single veined leaves associated and evolved as superficial outgrowth of the stem Microphylls first appear in the fossil recorda about 410 million years ago Megaphylls have a complex venation pattern and evolved from a branch system Megaphylls appeared about 370 million years ago at the end of the Devonian 5 The sporophyte became the dominant generation Sporophylls are modified leaves that bear spores Sporophylls may be grouped into conelike structures called strobili sing strobilus o Homospory production of one kind of spores Spores produce a bisexual gametophyte that produces eggs and sperms 0 Heterospory production of two kinds of spores Haploid megaspores develop into a female gametophyte Haploid microspores develop into a male gametophyte CLASSIFICATION OF SEEDLESS VASCULAR PLANTS There are two phyla of pteridophytes found in the modern flora Licophyta and Pterophyta 1 Phylum Lycophyta There are about 15 genera of lycophytes and approximately 1000 living species This phylum includes the Lycopods club mosses Selaginella spike moss and lsoetes quillwort This evolutionary line extends back into the Devonian 409363 mya but were most prevalent in the wet swamps of the Carboniferous period 363290 mya They eventually split up into two evolutionary lines o The first were very large woody trees that did not survive in the drier climate at the end of and after the Carboniferous age In the Carboniferous some lycophytes were forest forming trees more than 35 meters tall 0 The second and the surviving group of Lycopods are the small and herbaceous trees Lycophyta remains became the largest coal deposits of all geologic time The sporophytes of lycophytes consist of true roots stems and leaves microphylls Some Selaginella are 39 l I quot is 39 Sporophylls are specialized leaves that bear sporangia and are organized into a structure called the strobilus pl strobili 2 Phylum Pterophyta Psilophytes whisk ferns It includes two living genera Psilotum and Tmesipteris from tropical and subtropical regions of the world Sporophyte with a dichotomoust branching aerial and subterranean stem system True roots lacking Underground stems with rhizoids and with a fungal association Aerial stems lacking leaves but with scalelike or larger leaflike structures enations Until recently they were placed in a phylum of their own but DNA sequences analysis and sperm ultrastructure study has shown that they are related to present day fern The lack of roots and leaves may be due to simplification a derived or secondary characteristic ratherthan a maintained characteristic from ancient ancestors a primitive characteristic Sphenophytes Horsetails Sphenopsids extend back to the Devonian 409363 mya and reached their maximum development in the Carboniferous 363290 mya A family of one extant genus Equisetum ca 15 species of nearly worldwide distribution in damp habitats such as riverbanks lakeshores and marshes Michigan is a center of diversity for the genus with nine native species 0 The sporophyte of Equisetum is differentiated into an underground rhizome that bears adventitious roots and an upright photosynthetic stem with whorls of microphylls o Tough perennial herbs with jointed ridged aerial stems with distinct nodes 0 Stems rough accumulating silica and metals and complex anatomically o The aerial stems contain a large central pith region which in mature plants is hollow o Surrounding the pith cavity are discrete bundles of vascular tissue this arrangement of conducting tissue is known as a eustele Recent molecular data suggest that they are closely related to ferns and should be classified with them Ferns The fossil record of ferns extends back into the Carboniferous 363290 mya but their origins is in the Devonian 409363 mya There are about 12000 species of ferns in the world Most species are tropical gt There are about 380 species of ferns in USA and Canada gt Costa Rica has over 1000 species gt Philippines has over 950 species Sporophyte is differentiated into true roots stem rhizome and leaves megaphylls Leaves usually differentiated into Stipe petiole and blade with a central rachis or vein Most ferns are homosporous a few aquatic genera are heterosporous The sporangia are produced in clusters called sori sing sorus the sori can be arranged in various patterns e g rows or lines COAL FORESTS The Lycophyta and Pterophyta represent the modern lineages of seedless vascular plants that formed forests during the Carboniferous period about 290363 million years ago The coal beds oil fields and natural gas deposits that are mined in modern times are derived from these ancient forests From there comes the name fossil fuels During the Carboniferous Europe and North America were closer to the equator and covered with extensive swamps As plants died their body did not completely decay in the stagnant water and great depths of organic material accumulated forming peat These layers of peat were later covered by sediments that pressed the peat Pressure and heat converted the peat into coal petroleum and gas Chapter38 ANGIOSPERM REPORDUCTION AND BIOTECHNOLOGY The life cycle of angiosperms is characterized by an alternation of generations in which the haploid n and diploid 2n generations take turns producing each other 0 Sporophyte generation is diploid 2n and produces haploid spores through meiosis o Gametophyte generation is haploid n and produces haploid gametes through mitosis o Fertilization restores the diploid stage meiosis restores the haploid stage In flowering plants the diploid sporophyte generation is larger and nutritionally independent 0 The sporophyte produces spores by meiosis The haploid gametophyte generation which is located in the flower is microscopic in size and nutritionally dependent of the sporophyte o The gametophyte gives rise to gametes by mitosis The pollen grain is the male gametophyte of angiosperms Pollination is the transfer of pollen from the male structures to the female structures in the same or different flower Fertilization is a different process and takes place inside the ovary of the flower as does the development of the seed The ovary becomes the fruit another unique structure of the angiosperm STRUCTURE OF THE FLOWER The flower is a modified branch apex and is involved in sexual reproduction It is a unique structure of the angiosperms Flowers are a collection of organs designed to produce gametes attract gametes and develop seeds The flower is typically composed of four whorls of highly modified leaves called floral organs which are separated by very short internodes Flowers the reproductive shoots show determinate growth 0 Sepals petals stamens and carpels The whorls of organs sit on an enlarged branch end called the receptacle The sepals form the calyx and protect the flower bud The petals form the corolla and attract animals to assist in pollination Petals may or may not be present The stamens are the male reproductive organs 0 They consist of a filament and an anther Pollen grains form in the anthers Each pollen grain contains two cells one produces two sperm nuclei and the other produces a pollen tube to transfer the sperm nuclei to the ovule o A pollen grain represents a male gametophyte 339 e carpels are the female reproductive structures A flower may have one or several carpels Carpels may be separate or fused Carpel usually has a style and stigma Ovary is another name for the lower portion of the carpel An ovary may be formed by various fused carpels Pistil is another name for the female reproductive structure A pistil may be formed by a single carpel or by several fused carpels The ovary contains one or several ovules The ovule produces contains the embryo sac The embryo sac produces two polar nuclei and one egg The egg and the polar nuclei are involved in the process of double fertilization Variations in flower structure Floral whorls 0 Complete sepals petals stamens and carpels o Incomplete flowers lack one or several floral whorls Sexual parts of the flower 0 Perfect bisexual both stamens and carpels present 0 Imperfect unisexual the flower has only stamens staminate or carpels carpellate Sex of the plants 0 Monoecious the plant has both staminate and carpellate flowers flowers imperfect Dioecious staminate and carpellate flowers are found on separate plants flowers imperfect Hermaphroditic plant with flowers perfect quotOikosquot house eg monoecious one house Producing the male gametophyte ANTHER a SPOROGENOUS TISSUE 4 MICROSPORE a MICROGAMETOPHYTE POLLEN GRAIN a GENERATIVE CELL a MALE NUCLEI 1 The anther and the filament make the male reproductive organ of the plant 2 Inside the anther the diploid cells of the sporogenous tissue divide meiotically to produce haploid microspores 3 Each diploid cell produces four haploid microspores 4 Each of the four cells forming called now microspores divide mitotically to form pollen grains made of generative cell enclosed in a larger vegetative or tube cell 5 A very resistant outer layer of sporopollenin and an inner layer of pectin surround this twocell structure or pollen grain Producing the female gametophyte OVULE gt MEGASPORE gt MEGAGAMETOPHYTE EMBRYO SAC gt EGG 1 The ovule consists of an inner tissue called the nucellus and one or two protective layers called integuments 2 The integuments form one small opening at one end of the ovule the micropyle 3 One diploid cell in the nucellus produces four haploid cells or megaspores through meiosis 4 Three nuclei degenerate and one haploid nucleus remains 5 The functional megaspore enlarges at the expense of the other cells of the nucellus 6 This nucleus inside the cell divides mitotically twice forming first four nuclei and then eight nuclei 7 The eight nuclei separate and form six small cells and one large cell the megagametophyte or female gametophyte 8 Three cells migrate towards the micropylar end one cell becomes the egg and the two others are called synergids eventually degenerate 9 Three other cells migrate to the end opposite to the micropyle These are called antipodal cells 10 Two nuclei remain the in the center of the large cell These two nuclei are called the polar nuclei 11 At this point this structure is called the female gametophyte or megagametophyte or embryo sac 12 The ovule now consists of the embryo sac and its integuments Interesting site httpwww emr marimna 39 facultvfarabeebiobkBioBookflowerslhtm Mechanisms that prevent selffertilization Some plants can selffertilize if pollen from the same plant fall on the stigma Other plants cannot selffertilize these plants are selfincompatible There are several mechanisms involved in the compatibility or not of the pollen and the stigma The S locus in the cabbage family The quotS locusquot consists in reality of three loci There are multiple alleles of these genes up to 50 The proteins coded by these loci are located one in the membrane of the stigma cells another in the cell wall of the stigma cells and the third is secreted by mature pollen grains If the proteins secreted by the pollen are the same as one or both of the proteins in the cell membrane and wall of the stigma the pollen grain does not form a pollen tube Similarity of alleles means that they are probable from the same plant If the proteins secreted by the pollen tube are different from both of those in the cell wall and the cell membrane of the stigma the pollen tube forms The pollen comes from a different plant PM P 01 a d 535 xsszg b 5 515a x5152 9 c 5 s15 xss2 Q onwmpmmmm M whimnutmimms After fertilization Fertilization is the fusion of gametes o It restores the diploid condition in the zygote The male gametophyte produces a long tube that grows through the stigma the style and enters the micropyle of the female gametophyte syn embryo sac The generative cell of the pollen divides to form two sperm nuclei that move into the pollen tube Double fertilization is a unique phenomenon that occurs in angiosperms only 0 Egg and one sperm form the zygote 2n 0 The two polar nuclei and the second sperm form the endosperm 3n The endosperm stores food for the developing embryo The ovule will develop into a seed and the ovary will develop into a fruit Like in animals after the fusion of gametes there is 0 an increase in the amount of Ca2 in the cytoplasm o a blockto polyspermy the fertilization of the egg by more than one sperm Endosperm development After double fertilization the triploid nucleus of ovule39s central cell divides mitotically forming a multinucleate large cell The liquid mass of the endosperm becomes multicellular when cytokinesis forms plasma membranes and divides the endosperm into many cells Then these cells develop cell wall around them and the endosperm becomes solid ln monocots and many eudicots the endosperm stores the nutrients that are going to be used by the embryo during germination In some eudicots the food reserves of the endosperm are completely exported to the cotyledons before the seed completes its development the mature seed lacks endosperm eg beans Em bryogenesis Embryonic development follows a pattern The zygote divides into two cells the terminal cell develops into the embryo proper and basal cell develops into a column of cells the suspensorthat brings in nutrients and gibberellins to the developing embryo The suspensor is short lived and undergoes a process of programmed cell death or apoptosis Proembryo globular embryo heartshaped embryo a mature embryo The mature embryo A mature embryo consists of a radicle hypocotyl one or two cotyledons and the plumule Radicle embryonic root Cotyledons embryonic or seed leaves Hypocotyl embryonic or seed stem Plumule shoot apex or meristem In some species the cotyledons absorb the food from the endosperm and become the storage structure e g beans peanuts In other species the food remains stored in the endosperm and their cotyledons are very thin Seeds of monocots have a single cotyledon The grass family has a specialized cotyledon called the scutellum The scutellum is thin and in contact with the cotyledon During germination the scutellum absorbs food from the endosperm and transfers it to the developing embryo The embryonic root is covered by protective sheath called the coleorhiza and the shoot apex by a sheath called the coleoptile The fruit Seeds are enclosed in fruits Fruits are ripened ovaries and may or may not include other parts of the flower The fruit protects the seed and aids in seed dispersal The ovary wall or pericarp thickens during maturation Fruits may be fleshy like pears and oranges or dry like wheat and string beans As the fruit ripens enzymes digest the cell walls and organic acids and starch are converted to sugars which may reach a concentration of 20 in some cases Dry fruits have a dry pericarp and are usually confused with seeds e g wheat corn and acorns Simple fruits develop from one ovary eg peach or several fused ovaries eg tomato Aggregate fruits develop from many separate carpels of one flower eg blackberry Multiple fruits develop from many carpels of many flowers eg pineapple and fig Seed dormancy As the seed matures it dehydrates and enters a phase referred to as dormancy to sleep o Dehydration 0 Low metabolic rate 0 Suspension of growth and development Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling Seed dormancy is characteristic of plants that live in seasonal climates There is not one single mechanism involved in seed dormancy In some plants dormant seeds have high concentration of abscisic acid ABA which inhibits germination When the dormant seeds are exposed to water the abscisic acid washes out and germination starts Desert plants have phenolics compounds that inhibit dormancy During the short rainy season the phenolics compounds are washed away and the seed germinates when there is water available Some seeds have a very thick and resistant coat that does not allow water or oxygen to reach the embryo These seeds must be scarified by abrasion fire or passage through the digestive track of an animal Other seeds must undergo a period of cool or freezing weather before germination Some varieties of lettuce require light to germinate other plant seeds are inhibited by light Seed germination During germination glucose breakdown may be entirely anaerobic Increase in water uptake oxygen consumption and protein production After hydration enzymes begin the digestion of food in the endosperm or cotyledons and nutrients are transferred to the embryo Cells enlarge and the embryo burst through the seed coat Radicle emerges and begins to penetrate into the soil Hypocotyl elongates The process is controlled by mRNA stored in the seed ln dicots o The primary root emerges through the seed coats while the seed is still buried in the soil and grows down The hypocotyl emerges from the seed coats and pushes its way up through the soil It is bent into what is called the hypocotyl arch o The two cotyledons protect the epicotyl structures the plum ule from mechanical damage Once the hypocotyl arch emerges from the soil it straightens out This response is triggered by light Both red light absorbed by ph ochrome and blue light absorbed by cryptochrome can do the job 0 The cotyledons spread apart exposing the epicotyl consisting of two primary leaves and the apical meristem o In many dicots the cotyledons not only supply their food stores to the developing plant but also turn green and make more food by photosynthesis until they drop off In monocots o The primary root grows through the seed and fruit coverings and grows down into the soil 0 The first or primary leaf grows up protected by the coleoptile as it pushes up through the soil 0 The coleoptile stops growing once it reaches the surface then the primary leaf pushes through its apex and begins to expand Source httn39lusers rrn quot39 39 39 quot ma ultranetBioquyPaqesGGerminatinn html ASEXUAL REPRODUCTION Sexual and asexual reproductions are complementary in the life of plants Asexual reproduction enables successful clones to spread sexual reproduction generates the genetic variation that makes evolutionary adaptation possible Asexual reproduction is also called vegetative reproduction Offspring are formed without the fusion of gametes Offspring are genetically similar to the parent plant Stems leaves and roots may be adapted to asexual reproduction If a plant is very well adapted to a particular environment there is great advantage in producing offspring that are clones of the very well adapted parent Modified stems may give rise to independent plants in time by fragmentation The root system may give rise to many adventitious aerial shoots that eventually separate from the parent These new plants are clones of the original parent Apomixis is the formation of seeds without fertilization akin to parthenogenesis is animals 0 The new generation can come from an unfertilized ovule or from a vegetative cell 0 A diploid cell in the ovule gives rise to an embryo Modified leaves can produce plantlets that break off and give rise to new plants Vegetative reproduction of plants is common in horticulture Desirable varieties can be cloned from single cells taken from the parent plant Shoot or stem cuttings can be used to form undifferentiated masses of cells called a callus that eventually will form roots and a shoot Grafting allows combining the best characteristics of two plants 0 The plant that provides the root system is called the stock 0 The twig that is grafted is called the scion It is possible to grow whole plants by culturing small explants pieces of tissue cut from the parent on an artificial medium containing hormones and nutrients This method is used to propagate orchids and pine trees that produce wood at a very fast rate Protoplast fusion is a new method used to make plant hybrids from species that are sexually incompatible After the fusion of protoplasts the new cell is cultured using standard tissue culture techniques PLANT BIOTECHNOLOGY Biotechnology refers to any technique that uses living organisms or parts of these organisms Such techniques are used to make or modify products for a practical purpose Modern medicine agriculture and industry make use of biotechnology on a large scale Copyright GreenFacts asbllvzw 2001 2006 httpwwwgreenfactsorglgmol1 Agriculture began between 11000 and 10000 years From that time on humans have been selecting plants for their desired characteristics by means of artificial selection lnterspecific hybridization is common in plants and has been used by breeders to introduce new genes into crops Modern plant biotechnology uses techniques of genetic engineering to introduce genes of a species into the DNA of an unrelated species The genetically modified organisms are called GMOs These organisms that have genetically engineered to express a foreign gene from another species are called transgenic Genetically modified plants have the potential of increasing the quality and quantity of food There are many concerns about the unknown risks of releasing genetically modified organisms into the environment Effects on nontarget organisms Introduction of genes from GMOs to weed species that may become resistant to control methods Effects on human health related to the development of allergies effects of newly created proteins that are being ingested long term effects presently unknown antibiotic resistance etc Sleeper genes could accidentally be turned on and cause harmful effects Interesting sites on Chapter 43 NERVOUS SYSTEM The nervous endocrine and immune systems often cooperate and interact in regulating internal body functions to maintain homeostasis The ability of an organism to survive and maintain homeostasis depends largely on how it responds to internal and external stimuli A stimulus is an agent or a change within the body that can be detected by an organism Nerve cells are called neurons These cells are specialized for transmitting electrical and chemical signals through a network The nervous system consists of this network of neurons and supporting cells Neurotransmitters are chemical messengers used by neurons to signal other neurons and that allows the nerve impulse to be transmitted across a synapse or connection between neurons andor receptors EVOLUTION AND DIVERSITY OF THE NERVOUS SYSTEM The nervous system evolved over millions of years By the time of the Cambrian Explosion 545 million years ago a nervous system had already evolved Poriferans lack nervous system Nerve nets and radial nervous systems are characteristic of radially symmetrical animals 0 Nerve nets consist of scattered neurons impulses may flow in both directions of the synapse and the impulse weakens as it spreads from the point of stimulation 0 There is no CNS 0 Found in cnidarians Some cnidarians have two nerve nets one for slow fortentacle movement and another for faster to coordinate swimming 0 Echinoderms have a nerve ring and nerves that extend into various parts of the body Bilateral nervous systems are found in bilateral animals 0 Neurons aggregate to form ganglia nerves nerve cords and a brain 0 Cephalization includes the clustering of nerve cells at the anterior end of the animal 0 Planarians have two ganglia at the anterior end and two parallel nerve cords joined by transverse nerves o Annelids and arthropods have one or two ventral nerve cords that extend the length of the body An anterior pair of ganglia dorsally located is needed to respond adequately to stimuli and to coordinate input 0 Octopuses and squids have the most sophisticated nervous system of invertebrates They have large brains welldeveloped imageforming eyes and rapid signaling along giant axons FUNCTIONS OF THE NERVOUS SYSTEM The nervous system has three overlapping functions related to stimuli from within and without the body It is the master controlling and communicating system of the body It is responsible for behavior thought actions emotions and maintaining homeostasis together with the endocrine system Reactions to stimulus depend on four processes 1 Reception or sensory input afferent or sensory neurons and sense organs detect the stimulus 2 Integration involves sorting and interpreting information and determining proper response 3 Response or motor output efferent neurons bring the proper message to muscles and glands Neurons that transmit messages to the central nervous system CNS are called afferent or sensory neurons Neural messages are transmitted from the CNS by efferent neurons or motor neurons to effectors muscles or glands The action by effectors is the response to the stimulus Signals are transmitted by nerves Nerves are bundles of neuron extensions tightly wrapped in connective tissue The nerves that communicate between the body and the CNS form the peripheral nervous system NETWORKS OF NEURONS 1 Neuron structure Nerve cells are called neurons 0 Atypical neuron has cell body dendrites and an axon Dendrites are short highly branched cytoplasmic extensions specialized to receive stimuli and send nerve impulses to the cell body In many brain areas the finer dendrites have thorny projections called dendrite spines The axon is a long extension sometime more than 1 meter long and conducts impulses away from the cell body The conical region of the axon where it joins the cell body is called the axon hillock An insulating layer called the myelin sheath surrounds many axons The axon ends in many terminal branches called axon terminals with a synaptic terminal or knob at the very end that releases neurotransmitters Axons may branch forming axon collaterals Axons outside the CNS and more than 2 pm in diameter are myelinated The junction between a synaptic terminal and another neuron is called a synapse The transmitting cell is called the presynaptic cell and the target cell is called the postsynaptic cell A nerve consists of hundreds or thousands of axons wrapped together in connective tissue 2 The Reflex Arc A reflex is the simplest nerve circuit It is called the reflex arc A reflex is an automatic response to a stimulus Sensory receptor gt sensory neuron gt interneuron in spinal cord gt motor neuron gt effector organ e 9 muscle The cell body of sensory neurons is located in the dorsal root ganglion There are many ganglia along the sides of the spinal cord A ganglion pl ganglia is a cluster of neuron cell bodies that usually perform a similar function If the cluster of cell bodies is located in the brain it is called a nucleus pl nuclei 3 Supporting cells Glia are supporting cells There are several types 1 Envelop the neuron to form and insulating sheath around them 2 Phagocytes that remove microorganisms and debris 3 Lines the cavities of the brain and spinal cord 4 Anchor neurons to blood vessels Until recently researchers assumed that glia play a supportive role without actually participating in nerve signaling Recent studies have suggested that some synaptic interactions do occur between glia and neurons Glial cells are sometimes called collectively neuroglia Vertebrates have six types of glial cells Four types of glia cells are found in the Central Nervous System CNS astrocytes oligodendrocytes and ependymal cells A Astrocytes are starshaped cells that anchor neurons to capillaries which are the nutrient supply line Tight junction anchor these cells to capillaries and contribute to the bloodbrain barrier which restricts the passage of most substances into the brain 0 They are involved in the exchange between blood and neurons e g take glucose from the blood and pass it to neurons in the form of lactic acid 0 Some are phagocytic 0 Some regulate the concentration of K in the extracellular fluid of the nervous tissue 0 Others recapture or regulate the concentration of released neurotransmitters l Oligodendrocytes envelop neurons in the CNS with myelin and insulate them 9 Schwann cells are found outside the CNS and form an outer cellular sheath around the axon called neurilemma and an inner myelin sheath 0 The plasma membrane of the Schwann cell is rich in myelin a white fatty substance that acts as an insulator o Gaps in the myelin sheath are called nodes of Ranvier Multiple sclerosis occurs when the myelin sheath around the axons deteriorates and is replaced by scar tissue The damage interferes with the conduction of the nerve impulse The cause of MS is a mystery but there is some evidence that indicates that it is an autoimmune disease ION PUMPS AND ION CHANNELS lon pumps and ion channels maintain the resting potential of a neuron Most animal cells have a difference in electrical charge across the plasma membrane more negative on the inside and more positive on the outside of the cell in the fluid o This is called the membrane potential The plasma membrane is said to be polarized when one side or pole has a different charge from the other side When this occurs a potential energy difference exists across the membrane If the charges are allowed to come together they have the potential to do work Neurons use electrical signals to transmit information MEASURING THE MEMBRANE POTENTIAL Microelectrodes are used to measure the membrane potential of neurons The voltmeter registers the membrane potential the difference in charge across the membrane A resting neuron is the one not transmitting an impulse For an impulse to be fired the plasma membrane of the neuron must maintain a resting potential It must be polarized The resting potential is the difference in electrical charge across the plasma membrane 0 The inner surface of the membrane is negative 0 The interstitial fluid surrounding the neuron is positive 0 An electrical potential difference exists across the membrane It is called the resting or membrane potential The resting potential of a neuron is 70 mV millivolts By convention it is expressed as 70mV because the inner side is negatively charged relative to the interstitial fluid GATED IONS CHANNELS The resting potential results from the diffusion of K and Na through ion channels that are always open these channels are said to be ungated Neurons also have gated ion channels which open or close in response to one of three kinds of stimuli 1 Stretchgated ion channels found in cells that sense stretch and open when the membrane is mechanically deformed 2 Ligandgated ion channels are found at synapses and open or close when a specific chemical signal binds to the channel 3 Voltagegated ion channels are found in axons and open or close when the membrane potential changes THE NATURE OF THE NERVE IMPULSE Action potentials are the signals conducted by axons Graded potentials are called graded because their magnitude varies directly with stimulus strength 0 Hyperpolarization is an increase in the voltage across the membrane 0 Depolarization is a decrease in the voltage across the membrane The stronger the stimulus the more the voltage changes due to more channels opening and the farther the current flows Gated potentials are triggered by some change stimulus in the neuron39s environment Graded potentials are shortlived local changes in membrane potential that can be either depolarizations or hyperpolarizations These changes cause current flows that decrease in magnitude with distance PRODUCTION OF ACTION POTENTIAL Depolarization of a neuron s membrane is graded up to a particular voltage called the threshold voltage The nerve impulse is an action potential A Threshold phase Electrical chemical or mechanical stimulus may alter the membrane39s permeability to Na The axon contains specific voltageactivated ion channels that open when they detect a change in the resting potential When the change reaches threshold levels the protein changes shape the channels open and Na flows into the cell while the K remain closed The membrane of a neuron can depolarize by about 15mV without initiating an impulse The threshold to open the voltageactivated sodiumion channels is 55mV B Depolarization phase Sequence of events 1 Transient increase in Na permeability Kgated channels remain closed 2 Followed by the restoration of Na impermeability repolarization phase 3 Increase of K permeability If the depolarization reaches the threshold it triggers an action potential The inside of the cells becomes positive Polarity reverses due to the influx of Na These causes a momentary reversal of polarity as the membrane depolarizes and overshoots to 35 mV creating a spike o The spike is an example of positive feedback After a few milliseconds the sodiumion channels close The closing depends on time rather than on voltage K channels also open but more slowly and remain open until the resting potential has been restored Once depolarization occurred in one portion of the membrane the adjacent areas also become depolarize and the ion gates open Once the depolarization reaches the threshold potential it triggers a greater depolarization This is done by a positive feedback mechanism This process is repeated creating a wave of depolarization until the depolarization reaches the end of the axon The magnitude of the action potential is independent of the strength of the stimulus an allor none event C Repolarization phase Repolarization occurs in less than one millisecond later when the Na channels close and the membrane becomes impermeable to Na Leakage of K out of the cell also occurs and restores the interior of the membrane to its negative state Potassiumgated channels respond slowly and remain open longer K continue to leak out and this contributes to the temporary hyperpolarization ofthe membrane undershoot Sodiumpotassium pumps begin to function again This process restores the membrane to the usual resting potential of 75 mV When the membrane is depolarized it cannot transmit another impulse no matter how great stimulus is applied because the iongated channels are closed and unable to open This is called the refractory period when the membrane is insensitive to stimulus D Propagation of the nerve impulse along the axon The action potential is regenerated along the length of the axon 1 Na entering the cell creates an electrical current that depolarizes the next neighboring region of the membrane 2 In case of the action potential the depolarization is strong enough to reach the threshold in the neighboring regions reinitiating the action potential there 3 The membrane is repolarized in the previous region as K flow outward 4 The depolarizationrepolarization process is repeated in the next region of the membrane 5 Because of the refractory period the wave of depolarization cannot move backwards towards the cell body It can move only in the forward direction Continuous conduction occurs in unmyelinated axons In unmyelinated neurons the speed of transmission is proportional to the diameter of the axon o Axons with larger diameter transmit more rapidly o Squids and other invertebrates have large unmyelinated axons Resistance to the flow of electrical current is inversely proportional to the crosssectional area of the a conductor Many vertebrate axons are surrounded by a myelin sheath Myelin increases the conducting speed of action potentials by insulating the axon membrane The voltageactivated ion Na and K channels are concentrated at the nodes called nodes of Ranvier where the membrane is in contact with the interstitial fluid In myelinated axons depolarization action potential jumps from one node of Ranvier to the next This mode of conduction is called saltatory conduction saltare to leap in Latin It is fifty times faster than continuous conduction 120 meterssec COMMUNICATION BETWEEN CELLS AT SYNAPSES A synapse is the junction between two neurons or between a neuron and an effector o Neuromuscular junction or motor end plate is the synapse between a muscle and a neuron o Presynaptic neuron and postsynaptic neuron Signals across the synapse can electrical or chemical Electrical synapses contain protein channels gap junctions that connect the cytoplasm of two neurons and allow ions to flow directly from one neuron to the next o It allows the passage of ions from one neuron to the next and the impulse is directly transmitted 0 They occur between axons and cell body cell body to cell body dendrites and axons axons and axons dendrites and dendrites o For quick communication and coordination between many neurons Chemical synapses are separated by the synaptic cleft 0 Most synapses are chemical 0 Chemical messengers or neurotransmitters conduct the message When depolarization reaches the end of the axon it cannot jump across the cleft The electrical signal is converted to a chemical one Neurotransmitters are the chemicals that conduct the signal across the synapse and bind to chemically activated ion channels in the membrane of the postsynaptic neuron Synaptic vesicles at the tip of the axon contain neurotransmitters 1 Arrival of the depolarization wave opens calcium channels and allows Ca2 influx into the axon terminal 2 Ca2 act as messengers that cause the vesicles to fuse with the axon39s membrane and release the neurotransmitters into the cleft by exocytosis 3 Ca2 are quickly removed from the cytosol either taken up by mitochondria or ejected by calcium pumps 4 Neurotransmitters diffuse across the synaptic cleft and binds reversibly to specific protein receptors clustered on the postsynaptic membrane 5 Binding of neurotransmitters causes the protein receptors to change shape and open ion channels that initiate a depolarization wave in the postsynaptic neuron 6 Neurotransmitters are quickly destroyed by enzymes or reabsorbed by the presynaptic neuron 7 Removal of neurotransmitters closes the ion channels and terminates the synaptic response DIRECT SYNAPTIC TRANSMISSION Binding of neurotransmitters causes the protein receptors to change shape and open ion channels that initiate a depolarization wave in the postsynaptic neuron This is called direct synaptic transmission Each neuron may synapse with hundreds of other neurons Some of these synapses are excitatory and other inhibitory Presynaptic knobs may cover as much as 40 of the postsynaptic neurons39 dendrites and cell In excitatory synapses the binding of neurotransmitters open sodium channels and bring the membrane closer to the threshold making it easier to depolarize it o This is called the excitatory postsynaptic potential or EPSP In inhibitory synapses the neurotransmitters open potassium ion channels making it easier for the K to leak out and for CI39 and hyperpolarizing the membrane making it more difficult to reach the threshold 0 This is called inhibitory postsynaptic potential or IPSP Both EPSP and IPSP are graded potentials that depend on the number of neurotransmitters that bind to the receptors of the postsynaptic neuron Several synaptic terminals acting on one postsynaptic neuron have a cumulative impact on the membrane potential at the hillock bringing it closer to the threshold 0 This additive effect is called summation o In temporal summation the presynaptic neurons transmit to the postsynaptic neuron in rapid succession o In spatial summation several different synaptic terminals stimulate a postsynaptic cell at the same time and have an additive effect Summation is also applicable to IPSP INDIRECT SYNAPTIC TRANSMISSION In indirect synaptic transmission a neurotransmitter binds to a receptor that is not part of an ion channel This activates a signal transduction pathway involving a second messenger in the postsynaptic cell Cyclic AMP cAMP is one of those second messengers o Neurotransmitter e g norepinephrine activates a G protein 0 G protein activates adenylyl cyclase which converts ATP to cAMP o cAMP activates a protein kinase which phosphorylates specific channel proteins in the postsynaptic membrane causing them to open or close NEUROTRANSMITTERS More than 40 different chemicals are known or suspected to function as neurotransmitters Each type of neuron is thought to release one type of neurotransmitter A postsynaptic neuron may have more than one type of receptors for neurotransmitters 1 Acetylcholine is important in muscle contraction and in the autonomic nervous system o It can be inhibitory or excitatory o It is released from motor neurons called cholinergic neurons and from the CNS 2 Biogenic amines are neurotransmitters derived from amino acids 0 Norepinephrine epinephrine and dopamine are biogenic amine or catecholamine derived from tyrosine o Biogenic amines mostly function within the CNS 0 Dopamine and serotonin affect mood and have been linked to depression attention deficit disorder Parkinson39s and schizophrenia result from lack of dopamine 3 Amino acids and peptides function as neurotransmitters in the CNS GABA gamma aminobutyric acid is an amino acid that inhibits neurons in the brain and spinal cord and produces IPSP Glycine glutamate and aspartate are amino acids that function as neurotransmitters Some neurotransmitters are small molecules that act rapidly Others are neuropeptides larger molecules that modulate the effects of the smallmolecule neurotransmitters 0 Substance P is an excitatory neurotransmitters involved in the perception of pain 0 Endorphins are neuropeptides that decrease the perception of pain They also produce euphoria and other emotional states 4 Gaseous signals of the nervous system Nitric oxide NO and carbon monoxide C0 are local regulators 0 NO is involved in the production of erection in males during sexual arousal by relaxing the smooth muscles in the blood vessels in erectile tissue of the penis allowing the influx of blood 0 Viagra inhibits the enzyme that slows the musclerelaxing effects of NO Gaseous neurotransmitters are synthesized on demand and are not stored in vesicles VERTEBRATE NERVOUS SYSTEMS The vertebrate nervous system is regionally specialized In all vertebrates the nervous system shows cephalization and distinct CNS and PNS components Brain ventricles Central Spinal cord central canal Vertebrate Nervous Sensory Sensing external and internal environment Peripheral Somatic Motor Sympathetic Autonomic Parasympathetic Enteric Division 0 The somatic nervous system has receptors and efferent nerves from the CNS to muscles 0 The autonomic nervous system has receptors and efferent nerves from the CNS to organs Axons within the CNS are located in welldefined bundles ortracts whose myelin sheaths give them a whitish appearance the white matter The gray matter consists mainly of dendrite unmyelinated axons and clusters of nervecell bodies or nuclei The peripheral nervous system PNS consists of paired nerves and their associated ganglia Cranial nerves originate in the brain and extend to the head and neck and one pair the vagus into the thorax and abdomen 0 There are 12 pairs of cranial nerves The spinal nerves arise from the spinal cord and supply all parts of the body except the head and some areas of the neck 0 There are 31 pairs of spinal nerves Sympathetic NS permits the body to respond to stressful situations it is involved in arousal and energy generation o Preganglionic neurons transmit message from CNS to the paravertebral sympathetic ganglion chain and postganglionic neurons transmit the message to the effector o Nerves emerge from the middle region of the spinal cord 0 Most pathways consist of a chain of two neurons 0 Synapse is inside the ganglion o Sympathetic neurons release norepinephrine at their target organs Parasympathetic NS restores the body to resting state and actively maintains normal body functions 0 Parasympathetic preganglionic neurons synapse with postganglionic neurons in ganglia near or within the walls of the effector organs 0 Parasympathetic neurons release acetilcholine at their target organs Enteric Division consists of networks of neurons in the digestive tract pancreas and gallbladder Controls the organs secretions and peristalsis The enteric division can function independently but it is normally under the control of the sympathetic and parasympathetic nervous system EMBRYONIC DEVELOPMENT OF THE BRAIN The embryonic neural tube differentiates into three regions 1 Presencephalon orforebrain gt telencephalon gt cerebrum diencephalon gt thalamus hypothalamus 2 Mesencephalon or midbrain gt mesencephalon gt midbrain part of brain stem 3 Rhombencephalon or hindbrain gt metencephalon gt pons cerebellum myelencephalon gt medulla oblongata These primary divisions in turn differentiate to give rise to specific structures of the adult brain THE BRAINSTEM The medulla oblongata the pons and the midbrain are derived from the embryonic hindbrain They function in 39 39 quot quot of and conduction of information to higher brain centers The medulla and pons o The brain stem sends axons to the cerebellum and cerebral cortex by releasing norepinephrine dopamine serotonin and acetylcholine These signals cause changes in attention alertness appetite and motivation The medulla contains centers that control visceral functions including breathing heart and blood vessel activity swallowing vomiting and digestion o The pons contributes to some ofthese activities e g regulation of breathing All sensory and motor messages from the higher brain regions most pass through the brain stem to the rest of the body Conduction of information is one main function of the brainstem Coordinates large body movements such as walking Messages from the right side cross to the left side of the body and vice versa in the medulla Arousal And Sleep Sleep and arousal are controlled by several centers in the brainstem and cerebrum The reticular formation of the brainstem contains over 90 separate nuclei 0 Maintains consciousness and determines the degree of alertness o Receives messages from sensory receptors through the spinal cord and communicates with the cerebral cortex The more input the cortex receives the more alert the person is It filters out familiar and repetitive information that may cause a brain overload The pons and medulla have centers that cause sleep when stimulated and midbrain has a center that causes arousal Serotonin may be the neurotransmitter of the sleepproducing centers Melatonin produced by the pineal body seems to have an influence in the sleepwake cycle The function of sleep is not understood 0 One hypothesis is that sleep is involved in the consolidation of learning and memory THE CEREBELLUM The cerebellum develops from the metencephalon and is located dorsal to the pons and medulla lt processes and integrates information from the cerebral motor cortex and from receptors visual equilibrium etc and provides instructions to cerebral motor cortex about the precise timing and appropriate patterns of skeletal muscle contraction for smooth coordinate movements agility and posture The coordination occurs unconsciously lt checks for errors during motor perceptual and cognitive functions Cognitive functions learning decision making consciousness and an integrated sensory awareness of the surroundings THE DIENCEPHALON EPITHALAMUS THALAMUS AND HYPOTHALAMUS The forebrain gives rise to the thalamus hypothalamus and cerebrum o Telencephalon develops into the cerebrum o Diencephalon gives rise to the epithalamus thalamus and hypothalamus The epithalamus is the most dorsal portion of the diencephalon and forms the roof of the third ventricle o It includes the choroid plexus a cluster of capillaries that produce the cerebrospinal fluid 0 The pineal body is tiny projection of the epithalamus The thalamus incoming information from all the sense is sorted out in the thalamus and sent on to the appropriate higher brain centers for further interpretation in integration It is the gateway to the cerebral centers o It contains about 12 nuclei that receive information from a specific region of the cerebral cortex 0 lmpulses related to emotions visceral functions funnel through the thalamic nuclei The hypothalamus forms the floor of the third ventricle and receives olfactory messages and regulates the function of internal organs maintains homeostasis temperature respiration regulation of pituitary gland appetite etc o The hypothalamus contains the body thermostat that regulates hunger thirst and temperature o It regulates the sexual and mating behavior fightorflight response rage and pleasure The hypothalamus and circadian rhythms Animals exhibit regulatory rhythmic behavior e g seasonal reproduction migration sleep arousal etc Circadian rhythms is a physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues The biological clock is a component of the circadian rhythm In mammals a pair of structures called the suprachiasmatic nuclei SCN in the hypothalamus functions as a biological clock Cells of the SCN produce specific proteins under the influence of light The rhythm does no exactly match events in the environment and external cues are necessary to keep cycles timed to the outside world Visual information received through the eye keep the rhythm synchronized with the daily light and dark cycle 0 The human circadian rhythm is of 24 hours and 11 minutes THE CEREBRUM The cerebrum develops from the embryonic telencephalon In most vertebrates the cerebrum is divided into right and left hemispheres Each hemisphere consists of an outer covering of gray matter the cerebral cortex and internal white matter and a cluster of nuclei called basal nuclei deep within the white matter 0 White matter is made of myelinated axons 0 Gray matter cerebral cortex is made of cell bodies and dendrites The cerebrum is the largest and most prominent part of the human brain In humans the largest and most complex part of the brain is the cerebral cortex Sensory information analyzed motor commands are issued and language is generated in the cerebral cortex Characteristic to mammals is the neocortex an additional outer layer of cortex consisting of six sheets of neurons running tangential to the brain surface The neocortex is associated with greater cognitive ability and more sophisticated behavior The human neocortex amounts to about 80 of the brain mass Cerebral cortex is made of gray matter arranged into sulci White matter lies beneath the cerebral cortex Corpus callosum is made of axons and connects right and left hemispheres Axons are arranged into bundles tracts The basal ganglia a cluster of nuclei within the white matter are important centers of motor function Regions of the brain Regions of the brain are specialized for different functions Sensory areas receive information from senses and receptors Motor areas control the movement of voluntary muscles Association areas are the site of intellect learning memory language and emotion interprets sensory information The cortex has been mapped into areas responsible for certain functions Occipital lobe visual centers Temporal lobes auditory centers Parietal lobes receive information about heat touch and pressure Other areas are involved in complex integrative activities The size of the motor area in the brain for any given part of the body is proportional to the complexity of movement involved and not to the amount of muscle FUNCTIONS OF THE CEREBRAL CORTEX The cerebral cortex controls voluntary movement and cognitive functions The major increase in the size of the neocortex that occurred during mammalian evolution was mostly an expansion of the association areas that integrate higher cognitive functions and make more complex behavior and learning possible Information Processing In The Cerebral Cortex Sensory information is sent through the thalamus to the appropriate lobe from here the information is sent to adjacent association areas which associate the input with different types of senses and assess the significance of the overall sensory input The signals are then transmitted to still more association areas The association areas then compose an appropriate motor response which is used by the motor cortex to direct the movement of skeletal muscles The primary motor cortex and the somatosensory cortex are located and the rear of the frontal lobe The somatosensory cortex sends information to the motor cortex which in turn sends commands down the thalamus and spinal cord to skeletal muscles for a particular movement In both the motor cortex and the somatosensory cortex the neurons are distributed in an orderly fashion according tot eh part of the body that generates the sensory input of receives the motor commands See fig 4828 Lateralization of cortical function During early development brain functions are placed into opposite cerebral hemispheres and a division of labor is created This is called lateralization Each hemisphere has unique abilities not shared by its partner The left hemisphere is normally specialized for highspeed serial information processing essential to language and logic operations e g language mathematics logic operations and the processing of serial sequences of information The right hemisphere is stronger at pattern recognition nonverbal ideation and emotional processing e g face recognition spatial relations nonverbal ideation intuition artistic skills creative endeavors music emotional processing in general 0 Typical rightcerebral dominant people are lefthanded and male The two hemispheres have instantaneous communication with one another via connecting fiber tracts as well as complete functional integration Both hemispheres work together and never work alone at any task In some cases lateralization results in cerebral confusion and learning disabilities Language and speech Language is a process that involves multiple areas of the brain A large continuous region for language comprehension and articulation is located on the left hemispheres portions ofthe frontal and temporal lobes are involved The different areas of this region of the left hemisphere are 0 Wernicke39s area is involved in sounding out unfamiliar words 0 Broca39s area is for speech production A region to the anterior of the lobe is involved in language comprehension and word analysis Most of the lateral and ventral parts of the temporal lobe coordinate the auditory and visual aspects of language as when naming objects or reading Emotions The limbic system within the brain is involved in human emotions and memory It consists of a group of structures located in each hemisphere and surrounding the upper part of the brain stem Parts of the diencephalon the hypothalamus and the thalamus and inner parts of the cerebral cortex including the amygdala and the hippocampus make the limbic system The main limbic structures are the hypothalamus and the anterior nucleus of the thalamus Sensory areas of the neocortex and other brain centers the limbic system generates the feelings we generally call emotions