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Unit III Muscular System Structure and Physiology


Unit III Muscular System Structure and Physiology Chapter 10 – PowerPoint PPT presentation

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Title: 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
  • Generating heat (_______________)
  • Exercise, shivering

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

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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
  • Epimysium CT surrounds many fascicles to bundle
    a whole muscle together as an organ

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

Submicroscopic skeletal muscle
  • _____________ muscle fibers plasma mem.
  • Skeletal muscle fibers can have gt100 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

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

  • _____________- red, oxygen binding protein
  • only in muscle fibers
  • Contributes oxygen for ATP synthesis
  • Mitochondria- many in skeletal muscle
  • Myoglobin sarcoplasm have ingredients for ATP
  • 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

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  • ____________- appearance due to light I bands and
    dark A bands
  • ____________- small mesodermal cells
  • Embryonic skeletal muscle fibers arise from
    fusion of 100 or more
  • 100s 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

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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

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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
  • if graded potential reaches the axon
  • voltage-gated ion channels open?AP

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

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

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  • 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

  • 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
  • NMJ usually located at midpoint of muscle fibers
    propagate toward both ends

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

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

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

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  • _______- 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

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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

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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

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Calciums 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

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
  • If strenous activity more ATP made

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3 ways to produce ATP
  • _____________________________
  • Unique to muscle fibers
  • While relaxed, muscle making more ATP than needed
  • Excess ? creatine phosphate an energy rich
  • 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)
  • _______________________________
  • _______________________________

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

  • 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

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

Comparing isotonic isometric
  • ___________ contraction- iso same, tonic
  • 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
  • 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

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 (_at_2msec)
  • Ca2 being released from SR filaments exert
    tension, elastic components stretch, shortening

  • _______________ 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

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

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  • ___________ 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

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
  • 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

  • Wave summation- (summation of contraction) ?
    strength of muscle contraction that results when
    muscle APs occur one after another in rapid
  • ? 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

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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

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

  • Tonus Muscle tone - state of partial contraction
  • characteristic of normal muscle
  • maintained at least in part by a continuous motor
    impulses originating from reflex, and serves to
    maintain body posture
  • AKA muscle tone
  • ______________- wasting away or decrease in size
    of a part due to a failure, abnormality of
    nutrition, or lack of use
  • _______________- excessive enlargement or
    overgrowth of tissue without cell division

Cardiac muscle
  • Figure 20.9, table 10.2
  • Only in heart
  • forms most of the heart wall
  • Striated
  • Action is involuntary
  • alternating contraction relaxation cannot be
    consciously influenced.
  • beats due to pacemaker- ________________

Cardiac muscle (2)
  • Requires constant O2, many mitochondria
  • Hormones and neurotransmitters adjust heart rate
    by speeding or slowing the pacemaker
  • _______________- thickening of sarcolemma
    connecting ends of fibers together
  • Gap junctions to communicate from cell to cell

Smooth muscle, fig 10.18, 19
  • In walls of hollow internal structures
  • b.v., airways, and most organs of abdominopelvic
    cavity, also in skin and attached to hair
  • Looks ____________________________
  • Action is usually ___________, some also has
    autorhythmicity-built in or intrinsic rhythm.
  • Regulated by neurons of autonomic NS and by
    endocrine hormones
  • Compared to other types of muscle cells
  • Contraction usually slower, lasts longer
  • Can stretch and shorten to greater extent

Muscle disorders myopathies
  • Myopathy- signifies disease or disorder of
    skeletal muscle tissue.
  • Neuromuscular diesase problems at all 3 sites
  • Somatic motor neuron, NMJ muscle fibers
  • Myasthenia gravis autoimmune disease, chronic,
    progressive damage to NMJ
  • AB bind and block AchR at motor end plates
  • 75 of patients have hyperplasia or tumors of
  • Thymic abnormality may be the cause
  • 1st affects eye? swallowing, chewing,
  • Death may result from paralysis of respirtory
  • Anticholinesterase drugs (inhibits AchE)

  • Muscular dystrophy- group of inherited muscle
    destroying diseases
  • Degeneration of skeletal muscle fibers
  • DMD Duchenne muscular dystrophy
  • Mutation on X chromosome ? strikes males almost
  • Difficultly running, jumping, hopping
  • Unable to walk _at_12, resp or cardiac failure
    usually ? death between 20-30 yrs
  • Gene defect protein dystrophin
  • Little or no dystrophin, sarcolemma tears during
  • Gene therapy- inject myoblasts w/functional gene

  • _______________- painful, nonarticular rheumatic
  • Usually ages 25-50, 15X more in females
  • Affects fibrous CT components of muscle, tendons
    and ligaments
  • Pain at tender points from gentle pressure
  • Fatigue, poor sleep, headaches, depression
  • ______- sudden involuntary contraction of single
    muscle of large muscle group
  • __________- painful spasmodic contraction

  • ______- spasmodic twitching made involuntarily by
    muscles that are usually under voluntary control
  • Eyelid, facial muscles
  • _____________- rhythmic, involuntary, purposeless
    contraction that produces quivering or shaking
  • _____________-involuntary brief twitch of an
    entire motor unit that is visible under skin
  • _________________- spontaneous contraction of
    since muscle fiber that is not visible but can be
  • May signal destruction of motor neurons
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