BSC 215 Exam 2 Study Guide (Lecture)
BSC 215 Exam 2 Study Guide (Lecture) BSC 215
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This 24 page Study Guide was uploaded by Jordana Baraad on Saturday October 8, 2016. The Study Guide belongs to BSC 215 at University of Alabama - Tuscaloosa taught by Dr. Jason Pienaar in Summer 2015. Since its upload, it has received 74 views. For similar materials see Human Anatomy & Physiology I in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 10/08/16
Exam 2 Study Guide Key: Italics: uniquely differentiating or frequently tested concept Bold: key terminology CT = connective tissue ECM = extracellular matrix PM = Plasma Membrane RBC/ YBC/ WBC = red/yellow/ white blood cell RBM/ YBM = red/ yellow bone marrow SR = sarcoplasmic reticulum TC = terminal cisternae IMO = intramembranous ossification ECO = endochondrial ossification GAG = glycosaminoglycan AP = action potential Histology Histology: study of physiology of tissues 4 basic types of tissues: –Epithelial –Connective – Muscular – Nervous All have 2 main components: 1. Cells (unique to tissue type) 2. Extracellular matrix (ECM) (contains ground substance) Epithelial tissues structure – Supported by connective tissue beneath the basement membrane o Reticular lamina + basal lamina = basal membrane o Blood vessels for nutrition/ gas exchange – Specialized contacts / junctions btwn adjacent cells o Tight junction: proteins btwn 2 adj cells form impermeable seal o Desmosomes: IMPs interweave; resist mechanical stress o Gap junctions: protein pores allow material to pass btwn adj cells – Polarity: Associated with external environment or organ cavity o apical side: Associated with external environment or organ cavity growing surface; faces out o basal side: Associated with basal lamina (non cellular filter between tissue types) – Avascular: no blood supply – Regeneration – a lot of friction, need to regenerate if well nourished – innervated 2 broad types/ functions • Two broad types of epithelial tissue • Coverings & linings: Boundaries between diff environmentsexternal / internal Protection, absorption, filtration, excretion, secretion • Glands: Secrete mucous, sweat, enzymes, hormones etc endocrine: secrete products into bloodstream, no ducts exocrine: secrete products locally, via ducts Exocrine secretion modes Merocrine (eccrine): Products released as vesicles during exocytosis tear glands, pancreas, gastric glands, sweat Apocrine: part of cytoplasm broken off along with vesicles from apical portion Sim to merocrine (e.g. mammary glands) Holocrine: Cells accumulate product, then rupture to release it (e.g. sebacious glands on scalp) diff btwn secretion and excretion secretion—releasing something useful excretion—releasing waste *** epithelial tissue always assoc w/ connective tissue Classification – By thickness – Simple: One layer of cells attached to basement membrane – Stratified: 2+ layers of cells – By shape – Squamous – Flat and scalelike – Cuboidal – Cube shaped or squared – Columnar – Column shaped and tall Structure/ function/ location –italics signify defining/ most commonly tested characteristic Structure Function Location Simple squamous elliptically shaped filtration and Kidneys— cells with flattened diffusion (gases and Bowman’s capsules, nuclei nutrients); secretes glomerulus serous fluid Lungs—alveoli Circulatory system —endothelium Simple cuboidal Cubeshaped protection (against Excretory ducts Large, central abrasion, foreign Misc. organs/ glands nucleus particles, bacteria, Kidneys—tubules and excessive water Ovarian surface loss); absorption; Lungs—bronchioles transport Simple columnar Cells longer than Absorption, Most prolific cells wide protection in the body Large, circular constant nucleus, oriented regeneration Digestive tract, closer to basement female reproductive membrane, organs, nasal sometimes passage. innervated Stratified squamous Flat, compact, Protection against Epidermis, scalylike cells. mechanical and esophagus Can be keratinized physical damage, (dead, enucleated) chemical damage in or nonkeratinized the esophagus (living, present nucleus). Stratified cuboidal Commonly two Protection; Rare or columnar layered (but can be secretion Linings of large multilayered) ducts (salivary, Circular nuclei that mammary, sweat appear stacked. glands) Transitional Stretchy Distension to allow Walls of ureter, Constriction dome for water filling bladder, urethra shape cavity Stretching flat shape Pseudostratified Typ covered in cilia Secretion, Trachea, vas 1 row of misaligned absorption, deferens and cells movement (thru epididymis, can tell it’s not ciliary action) endometrium in multiple rows bc all females touch basement membrane goblet cells for secretion Connective tissue Function • Protects, supports, and binds together other tissues of the body i.e. bone, cartilage, etc. Immunity, movement, storage, heat production (brown fat), transport (blood) Structure • With the exception of cartilage, connective tissue is highly vascularized • Typically have few cells extensive nonliving material (matrix) between cells of connective tissue 3 main components o 1) Elastic and/or collagenous fibers (3 main types) 1. Collagen fibers provides tensile strength 2. Elastic fibers gives tissues distensible properties (stretch, compress) 3. Reticular fibers Network for support collagen + glycoprotein o 2) Ground substance (gellike substance with extracellular matrix) o 3) Cells (specific to cell type Classification • Connective tissue proper o Widely distributed throughout body o fibroblasts secrete ECM o many fiber types (collagen, elastic, reticular) o many cell types o Fibroblasts: produce/ maintain ECM o Adipocytes: Fat storage o Mast cells: immune/ inflammatory response o Phagocytes: ingest particles o Other immune cells o Highly vascularized o 4 subtypes – Loose (areolar) – Structure: – Cell type: fibroblasts – Fiber type: – thinelastic fibers – thicker collagen fibers Primarily ground substance. – Location: (most widespread) walls of hollow organs Surrounds blood vessels, nerves, and muscles Part of lamina of digestive and respiratory tract – Dense – Regular CT – Structure: – Fiber type: Primarily parallel collagen fibers – Thin nuclei run along fibers – Good for Resisting unidirectional stress – Function: Resists tension and pulling from a single direction – Location: Tendons and ligaments – Dense Irregular CT: – Structure: – Fiber type: collagen (closely packed) – Randomly arranged – Resist stress from every direction Location: Deep layer of thick skin (dermis), around joints, submucosa of digestive tract – Reticular Structure: Cell type: fibroblast Fiber type: reticular fiber (type III collagen) Function: gives support to soft organs – Location: Spleen, lymph nodes, bone, liver – Adipose – Cell type: Adipocytes consisting of fat (lipid) droplets – Nuclei at point of adipocytes – Location: Deep to the skin; surrounding heart and abdominal organs – Adaptation: consist of primarily adipocytes • Cartilage o Tough, flexible tissue resistant to tension, twisting and compressive forces o Cell type: Chondrocytes; housed in in lacunae o Avascular • 3 subtypes 1. Hyaline structure: fiber type: collagen (Large amount) Cell type: chondrocytes; found with the lacunae of ECM Chondrocytes are often found in pairs, location: Tissues in the ear, nose, trachea, larynx, and small respiratory tubules Synovial joints. Rib connection to sternum 2. Fibrocartilage structure: fiber type: collagen (spongier) cell type: chondrocytes; found in lacunae (often aligning) function: shock absorption location: ligaments, intervertebral disks, pubic symphysis, knee disks 3. Elastic Cartilage structure: fiber type: elastic (tightly packed) cell type: chondrocytes embedded in ground substance function: great dispensability/ flexibility to withstand bending location: Pinna (outer ear) and epiglottis • Bone o structure: o Hard calcified matrix o many collagen fibers o rocklike o very vascularized o cell type: osteocytes; lie in lacunae o Location: bones throughout body (obviously) o function: Supports and protects, calcium storage, rbc / wbc formation, mech movement • Blood o structure: o cell type: Red blood cells (erythrocytes) & white blood cells (leukocytes) ECM called plasma contains platelets, fat globules, gases, proteins, and hormones Red blood cells: donutlike, smaller than WBC’s Bone Tissue Bone Functions Support bears weight, cradles viscera and teeth Protection – protection of soft organ (e.g. skull, ribs) Movement – in conjuction with muscle Mineral storage & homeostasis calcium, phosphorous & magnesium metabolism Fat/ triglyceride storage—YBM houses adipose tissue Blood cell formation RBM produces red and white blood cells o More prevalent in infants o RBM confined to epiphyses after maturation Acidbase balance buffers blood against excessive Ph changes o (using above mentioned minerals as weak acids & bases) Overall bone structure Bone tissue = osseous tissue = cells + ECM Cells (2 lineages; 4 total types) Embryonic mesenchymal cells (ordered from least to most developed) Osteogenic cells: Highly mitotically active found in periosteum and endosteum (inside bone) some differentiate into osteoblasts (some remain osteogenic stem cells) Osteoblasts: Don't undergo cell division secrete collagen fibers that form bone matrix Fibers become encrusted with minerals like calcium Fibers attract hydroxyapatite crystals Osteoblasts are trapped in hardening matrix, become osteocytes Osteocytes: • Mature bone cells, trapped in Lacunae maintain bone matrix signal for bone repair or remodeling Embryonic monocytes Osteoclasts: Dissolve bone tissue (when signaled) Formed from blood cell lineages (monocytes) Found in resorption bays etched in the bone surface Secrete H+ ions & enzymes o acid dissolves bone; enzymes brk down protein o Daily remodeling of bones Side of osteoclast facing bone surface has a ruffled border o (increases cell surface area and ability to resorb bone tissue) ECM Inorganic (65%) Hydroxyapatite crystals (*Ca* & P) Bicarbonate, K, Mg, Na Organic / osteoid (35%) Collagen fibers Proteoglycans (protein > sugar) “bottlebrush” slows pathogens connects ECMs of adjacent cells GAGs (sugar >>> protein) Charged Attract water Glycoproteins (sugar > protein) Bind PM to ECM components Types of bones and their defining characteristics (italics = unique to this bone type) Long bones – length > width Examples—majority of appendicular (peripheral skeleton) Tibia, fibula, etc regions Diaphysis: shaft Epiphysis: ends Growth (epiphyseal)plates: sites of bone elongation Separate epiphysis and diaphysis 2 sites (hyaline) cartilage: 1. epiphyseal plates 2. articular cartilage: covers areas at joints a. synovial fluid produced to allow ease of movement b. articulation = joint = place where to bones meet connective tissue Periosteum: 2 layers Outer dense irregular collagenous layer inner osteogenic layer—regneration/ remodeling bone stem cells—can make new bone cells perforating (Sharpey’s) fibers: extend into bone matrix collagen fibers Allow for pulling of bone covering motion of whole bone Endosteum: Reticular connective tissue lines marrow cavities contains bone stem cell Sim to inner layer of periosteumConstant remodeling covers trabecular surfaces of spongy bone nutrient foramina: tiny holes in bone tissue allowing blood vessels to penetrate osseous tissue Waste products diffuse fr central canal to venous syst compact bone encloses medullary cavity can exist indepenently Spongy (cancellous) bone • location: ends of long bone • Contains bone marrow RBM Produced by Hematopoietic cells “Cancellous” = makes RBM fills entire medullary cavity in infancy converted to YBM in adults confined to epiphyses; minimal YBM • Stores triglycerides majority of adult marrow cells • ***ALWAYS surrounded by compact bone • units = trabeculae bony struts, not actually spongey No osteons (not tight layers) No central canal Blood supply obtained from compact bone vessels Short bones: length = width Examples: carpals & tarsals Connective tissue Periosteum (see long bone description) Endosteum (see long bone description) Osseous tissue Compact bone (see long bone description) Only very thin layer Spongey (cancellous) bone (see long bone description) Housed in inner portion (not just ends) Contain relative large amount BM Flat bones: thin & broad Examples—majority of axial skeleton Skull bones, sternum, pelvis, ribs Connective tissue Periosteum (see long bone description) Endosteum (see long bone description) Osseous tissue Compact bone Spongey (cancellous) bone (see long bone description) **diploe = special term for flat spongey bone Housed in inner portion (not just ends) Contain varying amounts BM Contains most of adult RBM supply Wormian (sutural) bones found within skull sutures Irregular bones don’t fit in above categories Examples: vertebra Sesamoid bones: bones found within tendons Example: patella Ossification / Osteogenesis: formation of bone –2 ways • Intramembranous ossification • sites: Flat bones of skull and clavicle • Starting material = membrane of embryonic connective tissue start product: primary (woven) bone irreg arrangement (like dense irreg CT) Abundant osteoyctes (trapped in ECM) Little organic matrix (lack of hydroxyapatite matrix = main diff fr sec bones) Present dur embryonic devel or fracture repair Absorbed by osteoclasts replaced w/ secondary bone end product: secondary lamellae (bone) More inorganic matrix (stronger) Fully formed lamellae; crossover of collagen fibers (reg collagen fiber arrangement) steps: 1. produce spongey bone trabeculae around blood vessels Capillaries being surrounded become RBM 2. Mesenchyme condensation periosteum adjacent to spongey bone 3. Trapped cells become osteocytes beneath pereosteum sandwiching developing spongey bone Semihardened matrix; some deposition • Endochondral ossification (endochondrial = w/n cartilage) •site: rest of skeleton • Starting material = hyalin cartilage model start product: primary (woven) bone see structure above end product: secondary bone (lamellae) see structure above steps: 1. Hyalin cartilage model formed by chondroblasts in perichondrium a. (membrane). 2.1 Chondroblasts in perichondrium differentiate into osteoblasts deposit bone collar around the shaft grows towards the epiphyseal plates (perichondrium becomes periosteum). Hormonally controlled 2.2 internal chondrocytes inflate & die in primary ossification cent thin walls between them calcify leaves behind cavities, surrounded by calcified cartilage. 3. wave of chondrocyte death—2 bone cell types arrive; replace cartilage Osteoclasts arrive in the blood digest external (foramina) & internal calcified tissue creates the primary marrow cavity. Osteoblasts also arrive deposit layers of bone. Both cells types follow wave of 4. Secondary ossification center develops in epiphysis creating secondary marrow cavity. (repeat steps 13). After birth, epiphysis cavity fills with spongy bone 5. Hyalin Cartilage lim to epiphyseal plate plate = elongation occurs till late teens plate then replaced by bone to form epiphyseal lines signifies end of longitudinal growth/ maturation 2 directions bone growth: longitudinal—increase in length Chondrocyte division in epiphyseal plate **unique—only cite of chondrocyte division; typ, it’s osteoblasts Sim to hyaline cartilage model Progression thru 5 zones Zone of reserve hyaline cartilage: Reserve chondroblasts Small chondroblasts Can make more hyaline cartilage Zone of cell proliferation: Actively dividing chondrocytes As chondrocytes divide, push cells upward to elongate Growing epiphesial plates away from central zone Push toward zone of cell hypertrophy Zone of cell hypertrophy: Mature, expanded chondrocytes Maturity death zone of calcification Zone of cell calcification: Dead, calcified chondrocytes blood vessel invasion bone deposition Zone of ossification: Osteoblasts deposit bone tissue Become entrapped osteocytes Form secondary lamella Process continues until reserve hyaline cartilage depleted appositional—increase in width Osteoblasts underneath periosteum deposit new compact bone Sim to IMO—start w/ mesenchyme/ osteoblasts in periosteum With addition of Osteoclasts and secondary bone formation (osteons) around blood vessels to form Haversion canals Bone remodeling / deposition/ resorption 3 major hormones: 1. growth hormone a. liver produces glycogen (causes bone growth) b. takes E fr adipose tissue c. increases skeletal muscles d. increases mitotic activity of chondrocytes (zone of elongation) i. unique chondrocyte division main takeawy: more grh more height 2. testosterone: increases rate of appositional growth 2ndary growth: accel closure of epiphyseal plate causes more robust skull in both men and women; more in men 3. estrogen: Increases rate of longitudinal growth Potently accelerates closure of epiphyseal plate Also… thyroid hormones Parathyroid hormone Increases blood Ca by enhancing bone breakdown/ resorption Stimulates osteoclasts indirectly—bind to osteoblasts CalcitoninOpposite of parathyroid Decreases blood Ca by enhancing bone building/ depostion Inhibits osteoclast activity Bone structures osteon = structural unit • Elongated cylinder of concentric lamella rings • Collagen fibers in adjacent lamella twist in opposite directions gives strength lacunae: cavities that house osteons lamellae = layered ECM—3 types concentric: surrounding the central canal in a osteontubular interstitial: bony plates that fill in between the haversions system. circumferencial: underlie the periosteum and endosteum Central canals (haversian): Innermost osteocytes receive nutrients from blood vessels pass them through gap junctions and canaliculi to neighboring osteocytes Nutrient foramina: Openings on bone surface of perforating canals that allow capillaries and nerves passage through compact bone Cannaliculi: connect lacunae All bone has osteoclasts—for remodeling Muscle Tissue Muscle chars Contractility – protein fibers draw together—NOT shortening Excitability responds to stimuli (electrical or chemical) Conductivity conduct stimulus (electricity) Extensibility – can be stretched Elasticity – can return original state after stretching Structural Heirarchy Muscle (organ level) comprised of subunits –largest to smallest Epimyseium = membrane encasing entire organ Continuous w/ tendon (muscle + bone attachment) Muscles made up of Fassicles = groups/ bundles of muscle fibers/cells/ myocites Perimyseium = membrane encasing individual fassicles Muscle fibers: discrete cells; cellular level of muscle tissue Protypical cell structures present in modified/ stretched form Endomyseium = areolar CT that covers each muscle fiber, overlaying the Sarcolemma: muscle cell plasma membrane invagination = T tubule—part of triad/ action potential (below) Sarcoplasm: cytoplasm of muscle cell Release Ca ions into sarcoplasm musc contraction Sarcoplasmic reticulum: SER of muscle cell Regulates Ca ion concentration in sarcoplasm; Ca storage Contains transverse tubles part of triad (see action potentials below) Mitochonrion make ATP; lots needed for muscle cells Nuclei: multinucleated to control long, skinny cell Myofibrils: specialized cytoskeleton units—facilitate muscle contraction Myofibrils comprised of repeated segments of sarcomeres Proteins + myofilaments Dark A bands & light I bands = source of skeletal musc striation alternating Sarcomere = contractile unit of myocite/ muscle fiber/ cell Contain alternating segments of A&I bands AContains both thick (myosin) and thin (actin) filaments I—contains thin (actin) only H zone: middle of A band—only thick (myosin) filaments Zdisk: zigzag line bisecting I band; forms border of sarcomere Thin and elastic filaments anchor to Zdisks M line: point toward which microfilaments slide dur contraction Middle line of A band Structural proteins that anchor thick (myosin) filaments Comprised of different types proteins Troponin—binds Ca Tropomyosin (continuous strand along myofibril) Titin: elastic protein 2 types microtubules actin in thin tubules myosin in thick tubules Contraction Process Contractile unit = sarcomere; repeated units along length of myofibril steps 1. calcium ions bind to troponin 2. tropomyosin moves; active sties of actin are exposed 3. actin sites exposed 4. myosin heads pull on actin 5. thin and thick bands slide past one another toward M line 6. Zbands drawn closer together Keep in mind… A (dark) band Stays same dur contraction H &I band Narrow dur contraction Whole sarcomere contracts—NOT individual tubules Action Potential: quick, temporary change in membrane potential in single region of PM Helpful terms/concepts Na/K ATPase pump: uses E fr ATP hydrolysis tomaintain concentration gradient Moves 3 Na out; 2 K in more neg inside sarcoplasm than outside Electrical gradient (a.k.a. electrical potential) caused by charge separation across sarcolemma voltage = difference in electrical potential btwn 2 points membrane potential measures the inside relative to the outside negative potential means cytosol more negative than ECF **action potentials use voltagegated channels NOT ligandgated channels like w/ Ach (see below) Single action potential propagated along muscle fiber like ripple 2 steps: depolarization + repolarization 1. depolarization begin w/ no excitation at resting potential (85mV) stimulus reaches sarcolemma voltagegated Na channels open Na rushes in increasingly positive membrane potential (up to +30mV) 2. Repolarization Na channels close; voltagegated K channels open K leaves cell membrane potential reverts back to negative Return to resting potential K channels close end action potential From Action Potential to Muscle Contraction—3 phases (+ relaxation) Excitation phase 1. action potential arrives at axon terminal a. axon terminal = end of neuron 2. synaptic vesicles release Ach into synaptic cleft a. synaptic cleft: space btwn axon terminal and muscle fiber b. Ach (acetylcholine) = only neurotransmitter in motor neurons 3. Ach binds to ligandgated ion channels in motor end plate in sarcolemma a. **Ligandgated channels—NOT voltagegated 4. Ionchannels open and Na+ enters muscle fiber 5. Entry of Na+ locally depolarizes sarcolemma end plate potential a. Multiple end plate potentials needed to action potential i. Action potentials are irreversible Excitationcontraction coupling 1. end plate potential(s) action potential 2. action potential propagated down Ttubules a. invaginated Ttubule brings depolarization deep into fiber 3. Ttubule depolarization Ca channels open in SR Ca in cytosol a. Ttubule flanked on each side by terminal cisternae (TC) (extensions of SR) = triad b. Ttuble depolarization Ca channels in TC “twist” open Contraction phase 1. Ca ions bind to troponin a. shifted troponin position 2. Tropomyosin moves, exposing actin’s active sites for myosin binding a. Myosin head + actin molecule = crossbridge b. Crossbridge sliding filaments Crossbridge cycle 1. ATP hydrolysis “cocks” myosin head a. ATP binds to head; P cleave energy release cocking 2. Myosin head binds to actin—op degree crossbridge rel to thick filament 3. Power stroke: ADP and Pdetach fr myosin head myosin pulls actin toward Mline of sarcomere a. Crossbridge 45 detrees rel to thick filament 4. Binding another ATP myosinactin attachment broken a. **spasms of rigor mortis occur when lack ATP inability of myosin to detach from actin Relaxation 1. AchE (acetylcholinesterase) degrades remaining Ach ligandgated ion channels close final repolarization 2. Sarcolemma returns to resting membrane potential; Ca channels in SR close 3. Ca ions pumped back to SR [Ca] in cytosol back to resting level a. Active transport 4. Troponin and tropomyosin block active sites of actin relaxation Energy Sources Immediate: creatine phosphate kinase (CPK) Location: cytosol Instaneous production and depletion 1 ATP directly to cell Intermediate—anaerobic glucose catabolism: (glycolysis) Location: cytosol Produces 2 ATP (1 min energy) Longest time to produce/ use—aerobic glucose catabolism: (Krebs cycle) Location: mitochondria Requires oxygen Produces 36 ATP Nervous System • Organs of the nervous system (organ system level): • Brain (continuous w/ spinal chord, but diff function) • Spinal chord • Nerves NOT same as neuron Neuron = cell; nerve = organ—diff tissues coming together Terminology nerve = long, fibrous organ—job to transmit signals axon = part of nerve that transmits signal Nodes of Ranvier have voltagegated channels; signal jumps along nodes Myelin sheath covers non-nodes; keeps signal “on track” dendrite = part of nerve that receives signal; highly branched soma = neuronal cell body Axon hillock = point where soma and axon meet Action potential zone; “trigger zone” for action potentials Divisions Central Nervous System (CNS): central axis of body Contains: Brain, spinal chord Functions: 1. filters/ integrates sensory input a. filtration—distinguish btwn signals & random APs b. integration—combines info from all around body cohesive understanding 2. coordinate response Peripheral Nervous System (PNS) Contains: Cranial nerves—from brain; innervates everything above neck 12 pairs cranial nerves (pairs bc right and left are mirrored) Spinal nerves—from spinal chord; innervate everything below neck 31 pairs spinal nerves More subdivisions: Sensory division (afferent pathways—carry info brain) Somatic sensory division: non-internal organs brain Ex. skeletal muscles, skin, etc Visceral sensory division: signals fr internal organs brain Motor division (efferent pathways—carry info to brain) Somatic motor division Carry CNS-gen signals skeletal muscles Autonomic nervous system (ANS) CNS-gen signals smooth/cardiac muscles/glands Unconsciously controlled—involuntary Sympathetic and parasympathetic divisions Sympathetic: “fight or flight” Parasympathetic: “rest and digest” Nervous tissue Cells (80% tissue) 10% of cells – neurons axons—much longer than dendrites only max 1 axon per neuron dendrites = all other projections body/soma in center 90% of cells = neuroglia (supporting cells) ECM (20% of tissue) Ground substance--liquid glycoproteins—signalling; identification LO4: Neuron structure Length = 1mm to 1m in length Most amitotic –cannot undergo meiosis No centrioles If destroyed, NO regeneration excitable—respond to electrical/chem stimuli Cell Body contains nucleus & maintains cytoplasm • Produces all proteins required for nerve signaling • Numerous mitochondria for high energy needs • Nissl bodies (dark staining associations of ribosomes and rough ER) extensive ER • Golgi apparatus: transport materials up/down neuron Dendrites: Numerous, short, highly branched processes Large surface area for receiving signals • Generate local potentials BUT NOT action potentials local—decremental = gradual, not all/nothing; doesn’t nervous signal action potential—irreversible trigger to signaling Axons Always only 1 (if present) Leaving cell If part branches off, called collateral axon axon hillock = meeting point of soma and axon • Processes that can generate & conduct action potentials • Action potentials are turned into chemical signals at synaptic knobs (end axon) (secretion) • Range from micrometers to > 1 meter in length 1 m ex—nerve fr base of spine to pinky toe • Axon plasma membrane = axolemma, surrounds axoplasm ONLY cells that gen AP have PM called axolemma (NOT dendrite) • Often wrapped in myelin sheath Axonal transport Slow (13 mm / day—can take up to 3 yrs) Anterograde: Away from cell body Transports: Cytoskeletal & other proteins Slow because it is “stop & go” Fast (relative to “slow” transport—200 - 400 mm / day; 5-day process) Anterograde OR Retrograde Retrograde: going toward cell body transports: Vesicles containing substances (e.g. ACh) membrane bound organelles some viruses (e.g. rabies) that target CNS Neuron classification 3 main types multipolar neuron: 1 axon, many dendrites –polar bc 2 sides different bipolar neuron: 1 axon, 1 dendrite pseudounipolar neuron: 1 axon w/ collateral branch, no dendrites just generating an AP one side; needs to get guickly to other side soma just there to maintain axon Neuron functional grouping cell bodies of neurons grouping in common signaling pathways CNS: nuclei PNS: Ganglia axons of neurons grouping in common signaling pathways CNS: Tracts PNS: Nerves White matter = tracts Gray matter = cell bodies—mostly nuclei Used for integrating/ tracking info Neuroglia Functions: Hold neurons together, maintain extracellular fluid assist neural function, repair damaged tissue 6 types CNS (4) Astrocytes (star-shaped) Anchor neurons & blood vessels in place Maintain extracellular environment Helps facilitate AP Assist in bloodbrain barrier formation Force capillaries to close Works like tight junctions Repair damaged tissue ***Oligodendrocytes (compare to Schwann cells in PNS) form myelin sheaths around some CNS axons numerous extensions wrap around many axons **Wraps from outsidein NO neurolemma—nucleus/ organelles in centralized located Myelination begins after birth Microglial cells Act like macrophages in CNS tissue Destroy pathogen in less destructive way than typ immune cell Must preserve brain tissue Ependymal cells Line brain ventricles Produce cerebrospinal fluid Circulate cerebrospinal fluid with cilia PNS (2) ***Schwann cells (compare to oligodendocytes in CNS) Wrap around some PNS axons to form myelin sheath (a few others multiple axons are bundled in Schwann cells like a “multidog hot hog”Almost like a crude oligodendrocyte) ENTIRE cell wraps around part of 1 axon Squeezes cytoplasm w/ nucleus up (hydrophob) phospholipid bilayer insulates axon **Wraps from inside out Outer layer forms a neurolemma w/ nucleus & organelles Myelination begins in early fetal period Satellite cells—function unknown; supporting cells Nervous tissue regeneration CNS: Astrocytes form scar tissue (damaged neurons cannot be replaced) PNS: Axon regeneration possible if cell body & part of myelinated axon is present Neurons, once formed, cannot undergo mitosis (lost their centrioles) PNS axon repair After axon severed… 1. Wallerian degeneration: Phagocytes digest components distal to severance point 2. Growth processes form: Several proximal cell extensions sprout from axon connected to cell body 3. Regeneration tube forms: Schwann cells and basal lamina form a regeneration tube 4. Regeneration tube directs growth: growth process in tube stimulated to continue growing (growth factors released by tube) 5. Connection with target cell reestablished: Schwann cells for myelin sheaths, muscle atrophy halted Ion channels Leak channels: always open (e.g. Na and K channels in Na/K ATPase pump) Particles moving down conc. gradient Many more K than Na channels Gated channels: Voltagegated: excitation impulse change in voltage opening (e.g. Na channels in sarcolemma and axolemma) Ligandgated: binding specific ligand (e.g. Ach) opening Mechanically gated: mechanical deformation opening (e.g. osmotic channels) Neural electrophysiology Resting membrane potential = **70mV ** (comp to 85 mV in muscle cells) Na+/ K+ pump can be depolarized—made more positive OR can be hyperpolarized—made more negative repolarization also = make more neg (at nonresting potential) membrane more permeable to K+ Local potentials Depolarization or hyperpolarization initially— ∓ 10mV (60 or 80mV) Depolarization by Na entering cell Hyperpolarization by Cl entering cell Located in Dendrite or soma membranes Graded potentials (vary continuously in size)–depolarization & hyperpolarization Decremental = gradual Propagate through ligand/voltage gated Na channels Accumulate in dendrites, then Trigger action potentials at axon hillock only if signal is strong enough ( > 55mV) good for shortdistance signaling, NOT long Action potentials Axon membranes Depolarization only initially From 70mV to +30mV to 80 back to 70 All or nothing (either occur or don't) Nondecremental (same strength throughout axon) Propagate through ONLY voltage gated Na channels @ axon hillock & Nodes of Ranvier Only triggers if local potential signal is strong enough (55mV at axon hillock) mechanism for longdistance signaling Local Action Potential: the Na/K pump resting state 70 mV = resting potential: Na and K channels closed / resting stimulation 55 mV=threshold potential absolute refractory period: no further excitation possible Na gates fully open/ in activated stateNa rushes in increasingly positive membrane potential (rapid depolarization) +30 mV (max): Na gates close/ resting; K gates open / in activated state relative refractory period: greater excitation than normal needed for excitation K rushes out increasingly negative membrane potential (repolarization) 70 mV resting potential but K channels slow to close < 70 mV (hyperpolarization) K channels eventually close return to resting state Depolarization in section of axon adjacent Na channels activated—positive feedback Clicker Questions CQ1: type of junction that prevents water from flowing btwn cells? B. Tight junction CQ 2: Type of tissue that’s 1 layer; tall, elongated C. simple columnar epithelium CQ3: Simple columnar epithelial lines the air sacs of lungs, forms outer boundary of serous membranes, and lines blood vessels—T/F B: false—simple squamous is correct CQ 4: Glands single cells or organs made up of 2 or more tissues—true CQ 5: What type of secretion involves release of substances, such as saliva and seat, in secretory vesicles a. merocrine NOT… a. apocrine—it breaks off b. holocrine—whol new cell CQ: Which NOT a function of the skeletal system? A: B) vitamin storage and fluid homeostasis (vitamins not typ stores; need to be replenished) Yes—blood cell formation, fat storage (yellow bone marrow), support CQ. Which true dur musc contraction? C) H zone and I bands both narrow CQ 4: Intramembraneous ossification first develops primary woven bone from hyaline cartilage model, ten replace w/ secondary lamellar bone T/F? False—starts from mesenchyme, not hyaline—rest is correct CQ: Which NOT a function of the skeletal system? A: B) vitamin storage and fluid homeostasis (vitamins not typ stores; need to be replenished) CQ2 T/F—opening of voltage gated Kchanels depolarization? F. Kchannel opening repolarization CQ5: What cells actively underlie mitosis at zone of elongation of epiphysel plate? B. chondrocyte Blasts for all other tissue CQ. Which true dur muscle contraction? C) H zone and I bands both narrow CQ2 T/F—opening of voltage gated Kchannels depolarization? F. Kchannel opening repolarization Cq3 T/F? Ach acts to open voltage gated sodium ion channels in the muscle cell membrane? F—Ach opens ligandgated channels, not voltagegated CQ4 Troponin has higher affinity for Ca than it does for tropomyosin? True CQ5 Functional unit of muscle contraction found btwn 2 Z disc is C) sarcomere
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