Muscle Physiology: Contraction Mechanisms · Zoology

In 'Tetanus,' why is the muscle able to maintain a sustained contraction?

  1. Calcium remains high because the SR cannot reabsorb it between rapid stimuli
  2. The motor neuron ceases firing but chemical residue keeps the muscle active
  3. ATP is fully depleted, locking myosin heads in the attached cross-bridge state
  4. The actin filaments reach their fully extended length and cannot slide further
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Correct answer: Calcium remains high because the SR cannot reabsorb it between rapid stimuli

When stimuli arrive fast enough, the SR doesn't have time to reabsorb the calcium between shocks. This constant high calcium concentration keeps the troponin-tropomyosin complex out of the way, allowing for continuous cross-bridge activity.

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