1. Skeletal Muscle Physiology Muscle excitation and energy sources. Describe the roles of ATP in muscle function. Explain the sources of ATP for muscle function.

2. Muscle elastic elements recoil, muscle returns to resting length. End of contraction ACh destroyed by ACh-esterase in synapse Muscle repolarizes Ca 2+ returned to SR by Ca 2+ active transporter ATP hydrolysis (+Mg) reextends myosin head Titin is the largest polypeptide known (34,350 amino acids in length). It spans from the M to Z lines.

3. Energy for muscle function - uses of ATP  for cross-bridge cycle, myosin detachment from actin  for Ca 2+ return to SR, by active transport  for return of Na +, K + by sarcolemma ATPase pump

4. Energy for muscle function - sources of ATP GlucoseCreatine ~P Glucose, fat or protein

5. + creatine

6. Pyruvic acid (anaerobic) lactic acid (aerobic) … next slide Glucose is supplied by stored glucose (as glycogen) and plasma glucose

7. glucose Oxygen (plasma or myoglobin) + Pyruvic acid + 36 ATP Krebs cycle Citric acid cycle = Cellular respiration = Aerobic metabolism

8. Time Course of Contributions from Different Energy Sources Oxidative fast twitch glycolytic (white) slow twitch oxidative (red)

9. Skeletal Muscle Fiber Types innervating nerve is primary determinant of fiber type during development a motor unit is composed of homogenous fibers all human muscles contain mixture of three general fiber types –slow twitch (ST, oxidative, red) –fast twitch (FTa, fast-oxidative, red) –fast twitch (FTb, glycolytic, white)