Question

If ACh binds to ligand-gated Na⁺ channels at a synapse, what would happen if acetylcholinesterase was nonfunctional?

A. Na⁺ entry into the postsynaptic cell would be prolonged, resulting in a strong depolarization
B. Na⁺ channels would be unable to open, tesulting in no change in the postsynaptio membrane potential.
C. Na⁺ exit out of the postsynaptic cell would be prolonged, resulting in a strong hyperpolarization.

Answer 1

Without functional acetylcholinesterase, acetylcholine remains in the synaptic cleft, causing prolonged Na+ inflow and depolarization of the postsynaptic neuron, leading to potential overstimulation. Correct option is A. Na⁺ entry into the postsynaptic cell would be prolonged, resulting in a strong depolarization

Step-by-step explanation:

If acetylcholinesterase (AChE) is nonfunctional, Na+ entry into the postsynaptic cell would be prolonged because AChE is responsible for degrading acetylcholine (ACh) in the synaptic cleft. Normally, when ACh binds to ligand-gated Na+ channels at a synapse, it leads to the depolarization of the postsynaptic membrane as Na+ rushes into the neuron. However, without AChE's function, ACh cannot be degraded, which prevents the termination of the signal. This results in prolonged depolarization and potentially unwanted extended muscle excitation and contraction.

To clarify, the correct answer to the question is A: Na+ entry into the postsynaptic cell would be prolonged, resulting in strong depolarization. The extended depolarization can lead to continuous stimulation of the postsynaptic neuron or muscle fiber, which is not the normal physiological response and can be detrimental.