Unit III Muscular System Structure and Physiology

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Unit IIIMuscular System Structure and Physiology

• Chapter 10

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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

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

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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

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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

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• 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
• _______________________
• _______________________

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• _____________- 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

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

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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

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• __________________- 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

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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

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• 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

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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

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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

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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

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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

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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
  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)
• _______________________________
• _______________________________

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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

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• 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

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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

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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

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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
  begins

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• _______________ 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

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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

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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

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• 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

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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

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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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Definitions

• 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

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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- ________________

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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

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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
  follicles.
• 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

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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
  thymus
• Thymic abnormality may be the cause
• 1st affects eye? swallowing, chewing,
  talking?limbs
• Death may result from paralysis of respirtory
  muscles
• Anticholinesterase drugs (inhibits AchE)

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• Muscular dystrophy- group of inherited muscle
  destroying diseases
• Degeneration of skeletal muscle fibers
• DMD Duchenne muscular dystrophy
• Mutation on X chromosome ? strikes males almost
  exclusively
• 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
  contraction
• Gene therapy- inject myoblasts w/functional gene

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• _______________- painful, nonarticular rheumatic
  disorder
• 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

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• ______- 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
  recorded
• May signal destruction of motor neurons