Download Comparative Vertebrate Physiology

Comparative Vertebrate
Physiology
Skeletal muscle
Motor unit


Neurons plus muscles they innervate
Innervate 5 to 100 muscles
End plate potential


Depolarization at the neuromuscular
junction
Depolarization depends upon:
Size
Number of vesicles
Muscle tension


Active process of generating force
Types
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
Isotonic: change in joint angle
Isometric: no change in joint angle.
Tension without sliding
Twitch

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Brief threshold stimulus
Latent period (few msec.)
Contraction period
(10 - 100 msec.)
Relaxation period
(10 - 100 msec.)
Summation



Caused by stimuli in rapid succession
Tetanus
Refractory period is always honored
Contraction delay
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Cross bridges attach before muscle
tension is developed
Elastic properties of muscle
Twitch does not lead to full contraction
Summation leads to full contraction
Tension development

Factors effecting:


Number of fibers stimulated (large vs. small
muscles)
Frequency of AP’s

Tetanus causes fatigue
Neuromuscular fatigue

Physiological fatigue

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Depletion of ATP
Ach depletion (more likely)
Versus psychological fatigue
Tension development

Factors effecting:

Degree of muscle stretch
Types of skeletal muscles

Tonic fibers


slow, isometric contraction (e.g. postural
muscles)
Phasic (twitch) fibers

slow twitch (contract and fatigue slowly)
(e.g. postural muscles)
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
fast twitch oxidative (rapid, repetitive
movement) (e.g. flight muscle)
fast twitch glycolytic (few, rapid contractions)
(e.g. breast of domestic fowl; amphibians, reptiles)
Rigor mortis

Muscle stiffness
3 - 4 hr < 12 hours > 48 to 60 hr
Why?
 Ca++ influx
 no ATP = no detachment of myosin from
actin
 protein degradation
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