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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.
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
Creatine ~P
Glucose
Glucose, fat
or protein
+
creatine
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)