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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:
SizeNumber of vesicles
Muscle tension
Active process of generating force Types
Isotonic: change in joint angle Isometric: no change in joint angle.
Tension without sliding
Twitch 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
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 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) 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