Question 1

What happens during the rising phase of an action potential?

Accepted Answer

Once threshold is reached, voltage-gated sodium channels open and Na+ enters the axon. This makes the inside less negative and then positive relative to outside, producing depolarisation.

Question 2

Why does the inside of a resting neuron become negative?

Accepted Answer

The resting membrane is selectively permeable, and K+ is distributed mainly inside while Na+ is distributed mainly outside. The membrane potential is commonly represented as about -70 mV inside relative to outside, although the exact value can vary by neuron and condition.

Question 3

How does repolarisation differ from the Na+/K+ pump action?

Accepted Answer

Repolarisation is mainly caused by voltage-gated K+ channels opening and K+ leaving the axon. The Na+/K+ pump restores the concentration gradients by moving 3 Na+ out for every 2 K+ in using ATP, but it is not the immediate cause of the falling phase.

Question 4

What is saltatory conduction?

Accepted Answer

Saltatory conduction is the propagation of a nerve impulse from one node of Ranvier to the next. Myelin insulates the internodes, so local current travels under the sheath while the action potential is regenerated at the exposed nodes.

Question 5

Are nodes of Ranvier breaks in the axon?

Accepted Answer

No. Nodes of Ranvier are small exposed gaps between myelin segments, while the axonal membrane and axon remain continuous underneath. They are the locations where ion channels concentrate and the spike is regenerated.

Action Potential and Saltatory Conduction — Watch the Spike Jump

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Practice