Skeletal Muscle Physiology

Muscle excitation and energy sources.• Describe the roles of ATP in muscle

function.

• Explain the sources of ATP for muscle function.

• Muscle elastic elements recoil, muscle returns to resting length.

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

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

GlucoseCreatine ~PGlucose, fat or protein

+ creatine

Pyruvic acid

(anaerobic)lactic acid

(aerobic) … next slide

Glucose is supplied by stored glucose (as glycogen) and plasma glucose

glucoseOxygen(plasma or myoglobin)

+ Pyruvic acid

+ 36 ATP

Krebs cycleCitric acid cycle

= Cellular respiration

= Aerobic metabolism

Time Course of Contributions from Different Energy Sources

Oxidative

fast twitch glycolytic (white)

slow twitch oxidative (red)

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)