Question

Explain how an action potential when fired spreads to the rest of the axon.

Why does the action potential spread in only one direction (toward the axon terminal)?

Explain why action potentials are conducted more quickly and effectively (in terms of energy used) in myelinated cells than in unmyelinated cells.

Answer 1

Action potential travels from cell body to axon of a neuron when there is a change in polarity of axonal membrane which occurs due to mechanism of sodium and potassium pump.

The action potential always remains unidirectional from cell body to axon but never reversed, it occurs due to refractory period of sodium channel. During refractory period sodium channels of becomes inactivate after reaching to threshold impulse and passes to forward.

In myelinated nerve fibres action potential or impulse travels via saltatory mechanism in which impulse jumps from one node (Ranvier's node) to another and prevent from energy loss during conduction at remaining axon. Hence, nervous conduction also become more quick in them.