Why are action potentials usually conducted in one direction?

a) the nodes of ranvier can conduct potentials in only one direction.
b) the brief refractory period prevents reopening of voltage-gated na+ channels.
c) the axon hillock has a higher membrane potential than the terminals of the axon.
d) ions can flow along the axon in only one direction.
e) voltage-gated channels for both na+ and k+ open in only one direction.

B) The brief refractory period prevents reopening of voltage-gated Na+ channels.

Explanation:

Refractory period is a period during which neuron cell cannot be stimulated (depolarized) and this is why action potential does not re-stimulate the adjacent membrane that was previously depolarized. This is also the reason action potential can only travel in one direction from the neuron body towards axon.

Refractory period occurs because of the inactivation of voltage-gated sodium channels (while action potential is at its peak) which cannot be open for a certain period of time. and membrane cannot be depolarized.

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