[Campbell Biology P.1129] Sarin gas triggers paralysis and death because it inhibits the enzy... | Practice Question

Sarin gas triggers paralysis and death because it inhibits the enzyme that breaks down the neurotransmitter controlling skeletal muscles. Based on this information and the text provided, what is the most likely primary effect of sarin gas at the neuromuscular junction?

  • A: It directly blocks acetylcholine receptors, preventing muscle contraction.
  • B: It prevents the reuptake of acetylcholine into the presynaptic neuron, leading to its prolonged presence in the synaptic cleft.
  • C: It inhibits acetylcholinesterase, leading to a prolonged excitatory postsynaptic potential (EPSP) at the neuromuscular junction, causing sustained muscle contraction and eventually paralysis.
  • D: It enhances the breakdown of acetylcholine, leading to a rapid cessation of muscle activity.
  • E: It causes the presynaptic neuron to release less acetylcholine, resulting in muscle weakness.

Explanation

The text states that sarin gas 'inhibits the enzyme that breaks down the neurotransmitter controlling skeletal muscles.' It then identifies acetylcholine as the neurotransmitter at the neuromuscular junction, where its excitatory activity is terminated by acetylcholinesterase, an enzyme that hydrolyzes acetylcholine. Therefore, inhibiting acetylcholinesterase would lead to a prolonged presence of acetylcholine in the synaptic cleft, causing continuous stimulation of muscle cells sustained EPSP , resulting in sustained muscle contraction spasms followed by paralysis due to receptor desensitization and depletion of cellular resources.