Acetylcholine exerts its effect by:

Question

BlackTom AI · Accepted Answer

The question asks how acetylcholine exerts its effect.
Option 1: 'binding to receptors at the motor end plate' is correct. Acetylcholine (ACh) acts by binding to nicotinic acetylcholine receptors on the motor end plate of the muscle fiber, causing depolarization and the subsequent muscle contraction.
Option 2: 'activating acetylcholine esterase' is inaccurate. Acetylcholine esterase (AChE) is the enzyme that breaks down ACh in the synaptic cleft after it has exerted its effect; AChE does not activate ACh’s effect, it terminates it.
Option 3: 'stimulating the motor neuron's synaptic knob' misstates the mechanism. ACh is released from the presynaptic terminal of the motor neuron when the nerve impulse arrives; the neurotransmitter then travels across the synaptic cleft to act on the muscle. ACh does not stimulate the motor neuron's synaptic knob to exert its effect.
Option 4: 'allowing calcium into the cell' is not the primary mechanism by which ACh exerts its action on the muscle fiber. While calcium influx into the presynaptic terminal triggers ACh release, the effect of ACh itself on the muscle depends on receptor binding and ion channel opening in the motor end plate, not on ACh-caused calcium entry into the muscle fiber.
Overall, ACh’s primary effect is to bind receptors at the motor end plate, initiating a cascade that leads to muscle contraction; the other options describe related processes (ACh breakdown, neurotransmitter release dynamics, and calcium roles) but do not describe the direct mechanism of action of ACh on the muscle.

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