CBSE Class 10 Answered

Nerve impulses travel in only one direction along the axon.

This is due to the refractory period. The opening and closing of the sodium and potassium channels during an action potential may leave some of them in a "refractory" state, in which they are unable to open again (inactivation) until the membrane potential returns to a sufficiently negative value for a long enough time. In the absolute refractory period, so many ion channels are refractory that no new action potential can be fired. Significant recovery (de-inactivation) requires that the membrane potential remain hyperpolarized for a certain length of time. In the relative refractory period, enough channels have recovered that an action potential can be provoked, but only with a stimulus much stronger than usual. These refractory periods ensure that the action potential travels in only one direction along the axon.