Skeletal Muscle Physiology cont.

1
Skeletal Muscle Physiology cont.

• Diagram the chemical and mechanical steps in the
  cross-bridge cycle and explain the effect on the
  muscle fiber length.
• Describe the end of contraction mechanisms.
• Muscle excitation and energy sources.
• Three roles of ATP in muscle function.
• Three sources of ATP for muscle function.

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Sliding myofilaments shorten sarcomeres
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• Excitation -contraction coupling
• ACh binds to, opens nicotinic Na/Kchannels
• Muscle depolarizes
• Ca2 released from sarcoplasmic reticulum
• Ca2 binds to troponin, cross-bridge cycling
  between actin myosin begins, filaments slide

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http//www.sci.sdsu.edu/movies/actin_myosin_gif.ht
ml
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• Draw and label a diagram to show the following
• stage of the cross-bridge cycle
• At rest, when the muscle is not stimulated.

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Skeletal Muscle Physiology cont.

• Diagram the chemical and mechanical steps in the
  cross-bridge cycle and explain the effect on the
  muscle fiber length.
• Describe the end of contraction mechanisms.
• Muscle excitation and energy sources.
• Three roles of ATP in muscle function.
• Three 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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• Draw and label a diagram to show the following
• stage of the cross-bridge cycle
• 2. At death when the muscle has depleted ATP.
  (rigor)

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Genetic mutationturns tot into
superboy4-year-old is first documentedhuman
case, scientists sayA German boy, seen here at
seven-months old, has a genetic mutation that
boosts muscle growth.
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Excitation-Contraction Coupling

• action potentials, generated at neuromuscular
  junction travel around sarcolemma and through
  T-tubules
• T-tubules signal SR to release Ca2 into
  sarcoplasm (cytosol)
• Ca2 saturates troponin (in non-fatigued state)
• troponin undergoes conformational change that
  lifts tropomyosin away from actin filament

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E-C Coupling (cont.)

• myosin head attaches to active site on actin
  filament forming cross-bridge
• after forming cross-bridge, myosin head moves
  actin-myosin complex forward and ADP and Pi are
  released
• ATP binds with myosin head, which releases actin,
  and returns to original position
• in resting state, myosin head contains partially
  hydrolyzed ATP (ADP and Pi)

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E-C Coupling (cont.)

• entire cycle takes 50 ms although myosin heads
  are attached for 2 ms
• a single cross-bridge shortens 10 nm
• as long as action potentials continue, Ca2 will
  continue to be released
• when action potentials cease, SR Ca2 pumps
  return Ca2 ceasing contractions
• skeletal motor units follow all or nothing
  principle