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Unit III Muscular System Structure and Physiology

Unit III Muscular System Structure and Physiology. Chapter 10. Muscle functions. Producing body motions Walking, running, nodding, grasping, etc. Stabilizing body positions Sustained contractions of neck hold head up Storing & moving substances within body GI tract, cardiac muscle

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Unit III Muscular System Structure and Physiology

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  1. Unit IIIMuscular System Structure and Physiology Chapter 10

  2. Muscle functions • Producing body motions • Walking, running, nodding, grasping, etc. • Stabilizing body positions • Sustained contractions of neck hold head up • Storing & moving substances within body • GI tract, cardiac muscle • Generating heat (_______________) • Exercise, shivering

  3. 4 Properties of muscle tissue • _________________ – respond to stimuli by producing electrical signals (AP) • ___________ – ability of muscle tissue to contract forcefully when stimulated by AP • _____________ – stretch w/out being damaged • ____________ – return to original length & shape after contraction or extension

  4. Structure of skeletal muscle, fig 10.1 • Each _______________________________ • composed of 100-1000s cells • * muscle ______= muscle _____ = myofibers • Endomysium = CT surrounds each fiber • B.V. & nerves penetrate into muscle • Perimysium = CT surrounds the fascicle • _______= 10s-100s of cells (fibers) bundled together • Epimysium = CT surrounds many fascicles to bundle a whole muscle together as an organ

  5. Structure of skeletal muscle (2) • All 3 layers of CT (endo, peri, epimysium) • protect and strengthen • extend from deep fascia - dense irregular CT bind muscles w/ similar function • ________ = fibrous membrane covering • Supporting & separating muscles

  6. Submicroscopic skeletal muscle • _____________= muscle fiber’s plasma mem. • Skeletal muscle fibers can have >100 nuclei just beneath the sarcolemma • ____________ = invaginations in sarcolemma • tunnel into center of fiber, filled w/ ECF • assists in exciting entire muscle fiber during AP • _____________-cytoplasm within muscle fiber • contains ___________________  ATP • stuffed w/ myofibrils

  7. Myofibrils – threadlike structures • contractile elements, extend entire length of muscle • Arranged in ___________- basic functional units • Striated appearance • Myofilaments - composed of contractile proteins • DO NOT extend whole length of fiber • 2 types: • _______________________ • _______________________

  8. _____________- red, oxygen binding protein • only in muscle fibers • Contributes oxygen for ATP synthesis • Mitochondria- many in skeletal muscle • Myoglobin & sarcoplasm have ingredients for ATP production: • O2 • Glucose • _____________________ (SR)- fluid-filled system of membranous sacs, similar to sER • in relaxed muscle stores Ca 2+ • release of Ca 2+ causes muscle contraction

  9. ____________- appearance due to light I bands and dark A bands • ____________- small mesodermal cells • Embryonic: skeletal muscle fibers arise from fusion of 100 or more • 100’s of nuclei • Satellite cells- myoblasts persisting in mature skeletal muscle • capacity to fuse w/ one another or w/ damaged muscle fibers • Regenerate functional muscle fibers

  10. Motor neuron & its muscle fibers • Figure 10.11- neuromuscular junction (NMJ) • __________________- motor neuron & all the muscle fibers it stimulates • __________________- region of sarcolemma that includes Ach receptors • Near synaptic end bulbs • ___________________ (NMJ)- a synapse between axon terminals of a motor neuron & sarcolemma of a muscle fiber

  11. Graded potential • ________________ from membrane potential that makes the membrane more or less polarized (Na+ & Ca 2+in, K+ out) • occur in dendrites & cell body of the motor neuron • if graded potential reaches the axon: • voltage-gated ion channels openAP

  12. All-or-none principle • When ______________ voltage is reached voltage gated channels will open and an action potential occurs • Different neurons may have different thresholds BUT the point is: • ________________________________ • Push over first domino, the rest fall

  13. __________________- molecules within axon terminals • Released into synaptic cleft in response to • Nerve impulse • Change in membrane potential • ___________________- NT released at NMJ • 1000s of molecules in each synaptic vesicle

  14. Acetylcholine receptor (AChR)- at each motor end plate 30-40 million • Transmembrane protein binds ACh • Binding opens ligand-gated ion channels • Acetylcholinesterase (AChE)- enzyme breaks down ACh, attached to ECM in synaptic cleft • ACh binding lasts only briefly • Breaks down excess not bound to receptor

  15. Nerve elicits a muscle action potential: • Release of ACh- diffuses across synaptic cleft. • Activation of AChR: binding opens gated ion channels allowing flow of small cations (most importantly Na+) • Production of muscle AP: inflow of Na+ inside fiber + charged, changing membrane potential, trigger AP • Termination of ACh activity: effect of ACh binding lasts briefly (ACh rapidly broken down by AChE) *NMJ usually located at midpoint of muscle fibers & propagate toward both ends

  16. Excitation - depolarization • Increased Ca 2+ concentration in cytosol initiates muscle contraction • [Ca 2+]  due to depolarization of muscle cell membrane = sarcolemma • AP from neuron  ACh receptors opening Na+ channels on the sarcolemma which depolarizes the muscle- muscle AP travels along T tubules causing SR to release Ca 2+

  17. Skeletal contraction & proteins • Myofibrils built from 3 types protein; • ________________ proteins- generate force • Actin and myosin • ________________ proteins- switch on and off • Troponin and tropomyosin • Both are part of the thin filament • ________________ proteins- proper alignment, elasticity, extensibility, link myofibrils to sarcolemma and ECM • 12: titan, myomesin, dystrophin

  18. Sliding filament theory fig 10.7,8 • Muscle contraction: • ______ heads attach & “walk” along _____ • Walking towards both ends of sarcomere • Thin filaments  M line • Thick filaments  Z disc • Length of thick and thin NOT changing • Sarcomere shortening  whole muscle fiber shortens  shorten entire muscle

  19. _______- motor protein (push and pull) • found in all 3 types muscle • 300 molecules/thick filament • ______________- convert chemical energy in ATP to mechanical energy of motion & force production • Shaped like 2 golf clubs twisted together • ______- molecules join to form filament in form of helix • On each actin molecule is a myosin binding site for myosin head to attach

  20. The contraction cycle, fig 10.8 • Ca 2+ released from SR • Binds troponin-tropomyosin complex & move it • In relaxed muscle, myosin binding sites are blocked by: • ______________- Are held in place by: _______________ • Contraction cycle can begin: • ATP hydrolysis • Myosin attaches actin, form crossbridges • Power stroke • Detachment of myosin from actin

  21. Contraction of skeletal muscle • Treadmill analogy • Myosin moving draws Z discs together • neighboring sarcomeres pulled together • Skeletal muscle shortens, pulls CT & tendons • Tension passes thru tendon, move bone • Fig. 10.11 to summarize contraction

  22. Calcium’s role •  [Ca2+] in cytosol starts contraction • (decrease stops contraction) • Muscle fiber relaxed: [Ca2+] low, BUT huge amt of Ca2+ stored in SR. • AP propogates along sarcolemma T tubules, ________________________ in SR membrane open • Ca2+ flows out into cytosol, combines with troponin to change its shape • Myosin binding sites are now free

  23. Sources of energy • Figure 10.12 • ______________: powering contraction cycle, pumping Ca2+ to SR for relaxation (& other metabolic rxns) • Relaxed state- modest amount used • Contracting- using at rapid pace • Amt present only enough for a few seconds of contraction • If strenous activity more ATP made…

  24. 3 ways to produce ATP • _____________________________ • Unique to muscle fibers • While relaxed, muscle making more ATP than needed • Excess  creatine phosphate – an energy rich molecule • Enzyme: creatine kinase (CK) catalyzes transfer of one phosphate of ATP to creatine creatine phosphate & ADP • When contraction begins, ADP levels  so CK transfers phosphate group from creatine phosphate back to ADP creating ATP (enough energy to last 15 sec) • _______________________________ • _______________________________

  25. Cellular respiration & muscle • Anaerobic- ATP-producing rxns, without O2 • Muscle activity but no creatine phosphate  glucose is catabolized to generate ATP • Glucose: blood  muscle fibers, & glycogen breakdown within muscle • Glycolysis: 1 glucose (10 rxns) 2 pyruvate yields 2 ATP • Pyruvic acid enters mitochondria & enters series of O2 requiring rxns to produce large amt of ATP • If no O2, pyruvic acid  lactic acid in cytosol • Liver cells take lactic acid  glucose

  26. Aerobic cellular respiration- series of O2 requiring rxns in the mitochondria produce ATP • muscle activity longer than ½ minute • Pyruvic acid ATP, CO2, H2O, and heat • Slower than glycolysis BUT yields more: • 1 glucose  36-38 ATP molecules. • F.a. molecule  over 100 ATP molecules • Oxygen comes from: • Diffuses into muscle from blood • Released from myoglobin within muscle fibers

  27. Motor unit recruitment • Process of ____________________________ • Typically different motor units in a whole muscle are NOT stimulated to contract in unison • Alternation delays muscle fatigue • Contraction of whole muscle can be sustained for long pds • One factor responsible for producing smooth movements rather than series of jerks • Recruitment causes small changes in muscle tension

  28. Comparing isotonic & isometric • ___________ contraction- iso= same, tonic= tension • Contraction where tension remains same • Occurs when constant load is moved thru the range of motions possible at a joint • Lifting a book off a table • _______________ contraction- iso = same, metric = measure • Contraction in which tension of the muscle increases but there is only minimal shortening so that no visible movement is produced • Holding a book in an outstretched hand

  29. Simple twitch figure 10.15 • __________________- brief contraction of all muscle fibers in motor unit due to a single AP in motor neuron • Myogram • Skeletal muscle twitch= 20-200msec • _____________ period- brief delay between application of stimulus & beginning of contraction (@2msec) • Ca2+ being released from SR & filaments exert tension, elastic components stretch, shortening begins

  30. _______________ period= 10-100msec • _______________ period= 10-100msec • Active transport of Ca2+ back into SR • Duration of all periods depends on type of muscle fiber (see table 10.1) • Fast twitch (as in eye) – 10 msec for each contraction and relaxation • Slow twitch (as in legs) – 100 msec for each contraction and relaxation

  31. Repolarization happens… • During the relaxation period Ca2+ is actively transported back to the SR • Refractory period= period of lost excitability • Characteristic of all muscle and nerve cells • Duration varies with muscle involved • Skeletal  5msec • Cardiac  300msec

  32. ___________ = minimum stimulus – the least amount of voltage required for contraction • _________________ – the voltage at which maximal force is generated (increasing voltage will not increase force of contraction) • All motor units are stimulated • All muscle fibers are contracting • Graded response (graded potential) – small deviation in the membrane potential that makes the membrane more polarized or less polarized

  33. Terms assoc. w/ frequency • _______________________________- • Maximal voltage applied to muscle in which all fibers in unit are stimulated • series of shocks at max voltage causes separate twitches • each twitch will stronger than the previous • Stimuli all at same intensity, cause muscle to contract more efficiently each time • May be warm-up effect, due to  intracellular Ca2+ needed for contraction

  34. Wave summation- (summation of contraction)  strength of muscle contraction that results when muscle APs occur one after another in rapid succession •  frequency =  strength of contraction • Tetany- fused tetanus -hyperexcitability of neurons & muscle fibers • Sustained or fused contraction • Continuous tonic muscular contractions – individual twitches not discerned • May be due to hypoparathyroidism

  35. Muscle fatigue • Inability to mantain force of contraction after prolonged activity • usually results from ∆ w/in muscle fiber • May feel tired, desire to cease activity • Central fatigue (CNS) • Mechanism unknown, possibly protective • Suspect contributing factors: • Inadequate release of Ca2+ from SR • Depletion of creatine phosphate (ATP levels not much change) • Insufficent oxygen, depletion of glycogen,build up of lactic acid and ADP, failure of AP to release Ach

  36. Recovery oxygen uptake • Formerly called ___________________ – the added oxygen that is taken into body after exercise • Recovery: few minutes to several hours depending upon intensity of exercise • Depletions during exercise: • Convert lactic acid  glycogen in liver • Resynthesize creatine phosphate & ATP • Replace oxygen removed from myoglobin • Post exercise oxygen needs remain high: •  body temp  chemical rxns • Heart & muscles still working hard   ATP use • Tissue repair processes

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