Skeletal Muscle Physiology Muscle excitation and energy sources. • Describe the roles of ATP in muscle function. • Explain the sources of ATP for muscle function.
End of contraction • ACh destroyed by ACh-esterase in synapse • Muscle repolarizes • Ca2+ returned to SR by Ca2+ active transporter • ATP hydrolysis (+Mg) reextends myosin head • Muscle elastic elements recoil, muscle returns to resting length. Titin is the largest polypeptide known (34,350 amino acids in length). It spans from the M to Z lines.
Energy for muscle function - uses of ATP • for cross-bridge cycle, myosin detachment from actin • for Ca2+ return to SR, by active transport • for return of Na+, K+ by sarcolemma ATPase pump
Energy for muscle function - sources of ATP Glucose, fat or protein Creatine ~P Glucose
Glucose is supplied by stored glucose (as glycogen) and plasma glucose Pyruvic acid (anaerobic) lactic acid (aerobic) … next slide
= Cellular respiration = Aerobic metabolism glucose Oxygen (plasma or myoglobin) + Pyruvic acid Krebs cycle Citric acid cycle + 36 ATP
Time Course of Contributions from Different Energy Sources fast twitch glycolytic (white) slow twitch oxidative (red) Oxidative
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)