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5.a&p i muscle2010

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Power Point I for Dr. Krasilovsky's Bio 110

Power Point I for Dr. Krasilovsky's Bio 110

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  • 1. Muscle Structure and Physiology Marieb: Chap. 9
  • 2. Muscles
    • I. Introduction
      • 1. Types of muscles:
        • a) Skeletal = Voluntary Striated
        • b) Cardiac = Involuntary Striated
        • c) Visceral = Involuntary Smooth/Nonstriated
      • 2. Properties:
        • a) respond to stimulus with contraction = excitability
        • b) passively stretched = extensible
        • c) return to original shape or length = elasticity
      • 3. Functions:
        • a) motion b) posture
        • c) heat production d) stabilize joints
  • 3. Fig. 9.1
  • 4. II. Skeletal Muscle A. Extramuscular Tissue
    • 1. Fascia - sheets of fibrous CT wrapped around muscle
    • 2. Epimysium - fibrous CT, extension of fascia
    • 3. Perimysium - separates muscle into individual bundles or fascicles
    • 4. Endomysium - separates into individual muscle cells or fibers
    • 5. Tendon -
      • a) cordlike CT connected to epimysium & bone
      • b) aponeurosis - broad, flat band connected to muscle or bone
  • 5. II. Skeletal muscle = Voluntary Striated
      • 6. Blood Vessels
        • a) outside perimysium but below or under epimysium = larger vessels
        • b) capillaries and small branches associated with endomysium layer
      • 7. Nervous Tissue
        • a) Travel with larger blood vessels
        • b) branches to individual muscles or groups of muscles
      • 8. Motor Unit - single motor neuron plus all muscle fibers it stimulates
        • 1 neuron can stimulate
          • 10 separate muscle fibers
          • 150 separate muscle fibers
          • 500 separate muscle fibers (Behavior?)
  • 6.
    • 9. Neuromuscular Junction (NMJ)
      • Point of contact or communication between neuron and muscle
    • 10. Motor End Plate
      • Specialized portion of muscle membrane at a NMJ
    Fig. 9.13
  • 7. B. Ultrastructure of Skeletal Muscle
      • 1. Sarcolemma - cell membrane
      • 2. Sarcoplasm - cytoplasm
      • 3. Multinucleated with many mitochondria
      • 4. Sarcoplasmic Reticulum (SR)
        • Smooth ER
        • SR usually in longitudinal direction
        • If SR is perpendicular to surface, right angles, known as Transverse SR or T-Tubules
        • Triad = one T-Tubule plus 2 SR
  • 8. Fig. 9.5 5. Endomysium surrounding single muscle fiber
  • 9.
      • 5. Endomysium surrounds single muscle fiber/cell
        • Up to 30 cm long and 10-100um diameter
        • Each muscle cell contains many myofibrils
          • Myofibril (1-2um) = bundles of myofilaments
        • Myofilaments = individual muscle filaments
          • Thick = myosin
          • Thin = actin or troponin or tropomyosin
        • Sarcomere = contractile unit, segment of a myofibril
      • 6. Myofilament Information
  • 10. Fig. 9.2a/b
  • 11.  
  • 12. Fig. 9.3
  • 13. Fig. 9.3
  • 14. Fig. 9.4
  • 15.
    • 6. Myofilament Information
      • a) Myosin - rod like tail terminating in two globular heads (sites of cross bridges)
        • Each thick filament = 200 myosin molecules with tails in the center and heads facing outwards on each side (away from H zone)
      • b) Actin - thin filaments that contain active sites where myosin bridges attach
      • c) Regulatory proteins on actin
        • Tropomyosin - spiral around actin and block actin sites to bind myosin at rest
        • Troponin - 3 sites: bind to actin, tropomyosin and calcium
      • d) Elastic (Titin) filaments - extend from Z disc to myosin to anchor myosin in place and help help muscle spring back after being stretched
  • 16.
    • 7. Anatomy of Relaxed muscle
      • Sarcomere - region of a myofibril between two successive Z discs/lines
      • Z disc = anchors the thin actin filaments
      • I band = extends from both sides of a Z disc, contains only thin actin filaments
      • A band = boundary of thicker myosin filaments plus contain some thin actin from I band
      • H zone of A band = less dense area where actin ends but myosin continues
      • M line of center of H zone = protein strands that stabilize myosin together
  • 17. Fig. 9.2 c/d
  • 18.
    • C. Sliding filament model of contraction Huxley 1954
      • 1. Thin actin filaments slide past the thicker myosin due to activation of myosin cross bridges to sites on actin
      • 2. Each cross bridge attaches and reattaches to move actin towards H zone
      • 3. H zone disappears
      • 4. I band shortens as Z discs move closer to each other
      • 5. A bands move closer to each other but do not change length since length of myosin does not change, only actin sliding over myosin
  • 19. Fig. 9.6 - 1 M
  • 20. Fig. 9.6
  • 21. Fig. 9.6
  • 22.
    • D. Physiology of Contraction
      • 1. ATP = energy chemical for contraction
        • Hydrolysis of ATP
        • ATP + H 2 O ADP + P + ENERGY
        • Energy used by cell for active transport, synthesis, and muscle contraction
        • Dehydration Synthesis of ATP
        • ADP + P + ENERGY ATP + H 2 O
        • Energy supplied from cellular respiration
  • 23.
    • D. Physiology of Contraction
      • 2. At rest -
        • a) Calcium stored in the SR (not free in the sarcoplasm)
        • b) ATP attached to the myosin cross bridge heads in relaxed position (not power position)
        • c) troponin-tropomyosin attached to actin filament - blocking the actin site for the myosin head :. NO ACTIN-MYOSIN ATTACHMENTS AT THE CROSS BRIDGES - NO TENSION
  • 24. FIG. 9.11
  • 25.
      • 3. Nerve becomes active/excites
        • a) conducts electrical charge down motor neuron axon towards terminal branch endings at neuromuscular junction
        • b) in the ending of the neuron, vesicles are present that contain the neurotransmitter chemical - nerves that stimulate skeletal muscles contain acetylcholine (ACh)
        • c) electrical current dies out in nerve ending but vesicles move towards nerve membrane and release ACh contents into NMJ via exocytosis
  • 26. FIG. 9.9 modified
  • 27. Fig.9.11 modified
  • 28.
      • 4. ACh diffuses across the space towards muscle membrane of motor end plate (net diffusion) where there are receptors for ACh on the muscle membrane
        • ACh will change membrane permeability to sodium and muscle becomes electrically excited and active in this region
      • 5. Excitation - Contraction coupling - the electrical changes on the muscle membrane lead to sliding of the myofilaments
  • 29.
      • 5. Excitation - Contraction Coupling
        • a) electrical changes on surface of sarcolemma spread down the T- tubules to the inner core of the muscle
        • b) remember - T-tubules meet the horizontal SR and form a triad
        • c) electrical changes of the SR cause Calcium (Ca 2+ ) to be released into the sarcoplasm by opening Ca 2+ channels of the SR
        • Ca 2+ is available to bind to the myofilaments
      • 6. Calcium is free in the sacroplasm
        • a) Ca 2+ activates the ATPase activity on the myosin head and powers the bending of the head
  • 30. Fig.9.11
  • 31.
      • 6b) Ca 2+ also displaces the troponin - tropomyosin complex from the actin binding sites (see Figure 9.10 & 11)
      • c) actin-myosin cross bridge forms and flips backwards pulling the actin past the myosin towards the center of the sarcomere
      • d) TENSION develops
      • e) one working stroke of head shortens muscle 1% - usual muscle shortening 30 to 35% - therefore each myosin cross bridge attaches and reattaches several times during a contraction
  • 32.  
  • 33.
      • 7. Nerve stops firing and stops releasing ACh
        • As long as ACh is in gap - keeps stimulating muscle and Ca 2+
        • ACh is destroyed in the space by an enzyme always present - acetylcholinesterase
        • Therefore - muscle membrane no longer electrically active and this cessation causes the free Ca 2+ to be transported BACK into the SR spaces via an ATP-dependent active pump
        • NO FREE CALCIUM
  • 34.
      • 8. Without free Ca 2+ - troponin-tropomyosin reoccupy the active site that binds myosin heads and cross bridges are broken and not reformed.
        • a) ATP is resynthesized and occupy the myosin binding sites
        • b) since cross bridges were broken - tension is lost and muscle returns to its original resting length
      • Myostenia gravis - problem with ACh receptor destruction
      • Rigor mortis - explain it?????
        • 3-4 hours muscle stiffens, maximum by 12 hrs
        • Dissipates over the next 2-3 days
  • 35.
      • 9. Creatine Phosphate
        • Muscles cannot store adequate ATP for continues muscle contractions
        • At rest:
        • ADP + P + Energy = ATP stored and on myosin
        • ATP + creatine = creatine-phosphate + ADP
        • Exercise:
        • ATP = ADP + P + Energy
        • Creatine-phosphate + ADP =creatine + ATP
  • 36.
    • E. Skeletal Muscle Physiology
      • 1. Single Twitch Phenomenon (lab)
        • a) single stimulus - threshold
        • Weakest stimulus that causes a muscle contraction
        • b) latent period (01. sec) - time between the stimulation and actual mechanical contraction of muscle
        • chemical / electrical change / Calcium
        • any tendon slack taken up first
        • c) contraction phase - developing tension (.04s)
        • d) relaxation phase (.05 sec) - calcium upt6ake and breaking cross bridges
  • 37.
    • e) fast muscle = 0.03 sec (insect 0.003 sec)
    • slow muscles = seconds
    • f) refractory period - no response to second equal stimulus, but a response to a stronger stimulus
    Fig. 9.14
  • 38.
    • g) 1) slow oxidative muscle - posture, marathon
      • red muscles (myoglobin) + mitochondria + abundant capillaries = high aerobic activity but slow ATPase activity
      • 2) fast glycolytic fibers - quick powerful movement - hitting baseball
      • White muscle low in myoglobin, more anaerobic and faster ATPase activity
      • Most muscle have a mixture of both
      • Table 9.2 textbook
  • 39.
    • 2. All or None Phenomenon
      • a) threshold - individual fibers respond maximally when stimulated
      • b) influenced by :
        • Temperature
        • Products of metabolism
        • Oxygen availability
        • Fatigue
      • c) muscle contain many individual fibers
        • Each fiber = all or none
        • Entire muscle has graded response determined by the number of fibers contracting
        • Entire muscle has a maximum response (100% fibers)
  • 40.  
  • 41. Fig. 9.16/17
  • 42.
    • 3. Summation - 2 consecutive stimuli with second response greater than the first
    • 4. Staircase or Treppe - stimulate muscle second time after it relaxes and compare tension
    Fig. 9.15b
  • 43.
    • 5. Tetanus - physiological response
      • a) many rapid responses to prevent relaxation (2)
      • b) fusion of twitches - continuous sustained contraction (4)
      • c) partial or incomplete tetanus - contractions do not fuse (3)
    • 6. Tonic Contraction
      • a) some cells contracted, others relaxed, interchange
      • Posture
      • Flaccid - less than normal tone to muscle
    Fig. 9.15-9.16
  • 44.
    • 7. Isotonic
      • a) same tone or tension
      • b) change in length during contraction
      • c) pick up a book
    Fig. 9.18a
  • 45.
    • 8. Isometric
      • a) same length
      • b) develop or change tension
      • c) try to left heavy object, push wall
    Fig. 9.18b
  • 46.
    • III. Cardiac muscle
      • 1. Involuntary, striated muscle
      • 2. Single nucleus, branched
      • 3. Intercalated discs
        • Area of low resistance to electrical flow of current - network contraction response
      • 4. Intrinsic rhythm - normal rate of pacemaker = 120+ per minute
        • Vagus nerve slows down intrinsic pacemaker to 60-80 beats per minute
      • 5. Refractory period - rest
        • No tetanus possible
        • High rate = fibrillation
  • 47. Fig. 18.11
  • 48.
    • 6. Skeletal vs. cardac contraction
      • Cardiac has longer tension due to calcium involved from both SR and extracellular environment
    Fig. 18.12
  • 49.
    • IV. Smooth Muscle
      • 1. Involuntary, nonstriated muscle
      • a) actin & myosin poorer organization of fibers
      • b) fibers attached to membrane or lattice in sarcoplasm
      • c) SR less developed
      • d) spindle shaped
    Fig. 9.28a/b
  • 50.  
  • 51.
      • 2. Type of Contraction
        • Slow contraction due to poor arrangement of fibers
        • Does not fatigue
        • Tonic type of contraction
        • Calcium involved from
          • SR
          • Extracellular
          • Movement is slower since there are no T-Tubules
        • See Fig. 9.29
  • 52.
    • 3. Visceral/single unit vs. Multiunit
    • a) sheets lining blood vessels a) larger blood vessels and walls of organs airways, eye muscles, arrector pili muscles
    • b) tight junctions between muscle cells
    • c) one nerve controls many different muscle cells, wave-like contraction
    • c) individual muscles with separate motor nerves