Which neurotransmitter chemical substance is released across synaptic clefts at human neuromuscular junctions to stimulate skeletal muscle contraction?
Answer and explanation
Correct answer: A. acetylcholine
- Step 1: When an action potential reaches the presynaptic axon terminal, voltage-gated calcium channels open, prompting synaptic vesicles to fuse with the membrane. Step 2. Acetylcholine (ACh) is released into the synaptic cleft, binding to nicotinic receptors on the motor end plate to trigger depolarization and contraction. Answer: acetylcholine. Why not the others: Glycine is an inhibitory neurotransmitter; melatonin regulates circadian sleep cycles; insulin is a pancreatic hormone.
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