1. Comparative Vertebrate Physiology
Skeletal muscle

2. Motor unit Neurons plus muscles they innervate
Innervate 5 to 100 muscles

3. End plate potential Depolarization at the neuromuscular junction
Depolarization depends upon:

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

5. Twitch Brief threshold stimulus Latent period (few msec.)
Contraction period ( msec.)
Relaxation period ( msec.)

6. Summation Caused by stimuli in rapid succession Tetanus
Refractory period is always honored

7. 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

8. Tension development Factors effecting:
Number of fibers stimulated (large vs. small muscles)
Frequency of AP’s
Tetanus causes fatigue

9. Neuromuscular fatigue
Physiological fatigue
Depletion of ATP
Ach depletion (more likely)
Versus psychological fatigue

10. Tension development
Factors effecting:
Degree of muscle stretch

11. 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)

12. 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