A neuron's membrane voltage potential is at its resting potential. Rapid depolarization of the cell membrane at the start of an action potential.....

Question

A neuron's membrane voltage potential is at its resting potential. Rapid depolarization of the cell membrane at the start of an action potential.....

	A.	(1)... occurs whenever a synaptic input is received by the neuron
	B.	(2)... occurs whenever a positive membrane potential input is received by a neuron
	C.	(3)... occurs due a rapid feed-forward cycle of increased Na+ conductivity and more positive membrane voltage.
	D.	(4)... occurs whenever there is sufficiently strong depolarizing input.
	E.	Answers marked (1) and (2) are both correct.
	F.	Answers marked (3) and (4) are both correct.
	G.	All of the answers are correct.

Answer 1

F) Answers marked (3) and (4) are both correct

When the dendrites of a neuron receive an excitatory stimulus that depolarizes the local environment, the change in potential to become more positive causes other sodium channels to open with greater ease, allowing for a greater influx of sodium into the cell. The opening of a few sodium channel can therefore create a more drastic depolarization by facilitating the opening of other channels. This is why (3) is correct. However, not all depolarizing stimuli are sufficiently strong to cause this rapid change and depolarization. This is why (4) is correct.

Answer 2

The correct answer is (C). As voltage-gated Na+ channels open, sodium ions quickly rush through into the neuron and momentarily give the neuron a positive membrane potential. This happens only when the gates are opened and enough Na+ enter the neuron, not simply after an input, so answers (1) and (2) are not accurate. Answer (4) sounds promising, but implies that depolarization can occur with ions besides Na+, which is not accurate. The answer is (C).