Refer to the figure showing a neuromuscular junction. Which event is occurring at position 5? A) Acetylcholine molecules are entering the postsynaptic cell. B) Ca²⁺ channels open after acetylcholine binding occurs. C) Charged acetylcholine molecules cause a graded potential in the postsynaptic membrane. D) The motor end plate is depolarized by the influx of Na⁺. E) Acetylcholinesterase breaks down acetylcholine, and the channel closes again.

Question

Quizplus · Accepted Answer

Position 5 is the motor end plate, where acetylcholine binding causes the opening of sodium channels and subsequent depolarization of the postsynaptic membrane. This is known as the end plate potential. Option A is incorrect because acetylcholine has already been released from the presynaptic neuron and is now binding to receptors on the postsynaptic membrane. Option B is incorrect because the opening of calcium channels occurs in the presynaptic neuron during neurotransmitter release, not at the motor end plate. Option C is incorrect because the end plate potential is an all-or-nothing response, not a graded potential. Option E is incorrect because acetylcholinesterase breaks down acetylcholine in the synaptic cleft, not at the motor end plate.

Refer to the Figure Showing a Neuromuscular Junction