Muscle Physiology Case Histories - Case 5

Prior to intubation for a surgical procedure, the anesthesiologist administered a single dose of the neuromuscular blocking agent, succinylcholine, to a 23-year-old female to provide muscular relaxation during surgery and to facilitate the insertion of the endotracheal tube. Following this, the inhalation anesthetic was administered and the surgical procedure completed.

1. Beginning with depolarization at the neuromuscular junction, describe the normal sequence of events which lead to muscle contraction.

2. What prevents acetylcholine (ACh) from accumulating in the neuromuscular junction and causing a sustained contraction in a normal individual?

3. Succinylcholine acts as a depolarizing agent that prevents repolarization of the nerve. Therefore, no further ACh is released until the drug is cleared. Name another site within the neuromuscular junction that might be affected to prevent muscle contraction. (Hint: curare acts by this mechanism.)

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