Skeletal Muscle Physiology

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Skeletal Muscle Physiology

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

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• 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.
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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

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Energy for muscle function - sources of ATP
Glucose, fat or protein
Glucose
Creatine P
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creatine
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Glucose is supplied by stored glucose (as
glycogen) and plasma glucose
Pyruvic acid
(anaerobic) lactic acid
(aerobic) next slide
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Cellular respiration Aerobic metabolism
glucose
Oxygen (plasma or myoglobin) Pyruvic acid
Krebs cycle Citric acid cycle
36 ATP
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Time Course of Contributions from Different
Energy Sources
fast twitch glycolytic (white)
slow twitch oxidative (red)
Oxidative
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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)