# Solve this: Q.171. The given nervous system figure illustrate the axonal membrane and propagation of nerve impulse what will be the direction of propagation of nerve impulse:- (1) X $\to$ Y (2) Y $\to$ X (3) Z $\to$ Y (4) Y $\to$ Z

Dear Student,

As signal triggers from another neuron, sodium/potassium channels open and close as the membrane reaches its threshold potential. As nerve impulse travels down the axon, there is a change in polarity across axonal membrane.

At the start of action potential, sodium channels open and Na+ moves into axon causing de-polarisation. Re-polarisation occurs when K+ channels open and K+ moves out of axon. Thus, there is a change in polarity across axonal membrane.

So, as given in picture in question, nerve impulse propagate from X to Y and then Y to Z. Option (1) and (4) are correct answers.

Regards,

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