Question

Unidirectional transmission of a nerve impulse through nerve fibre is due to the tact that

(a) nerve fibre is insulated by a medullary sheath

(b) sodium pump starts operating only at the cyton and then continues into the nerve fibre

(c) neurotransmitters are released by dendrites and not by axon endings

(d) neurotransmitters are released by the axon endings and not by dendrites.

Answer 1

Correct option (d) neurotransmitters are released by the axon endings and not by dendrites.

Explanation :

A synapse occurs where the axon of one neuron (the pre-synaptic neuron) meets the dendrite of another (the post-synaptic neuron). At the tip of the pre-synaptic axon is a button shaped swelling called a synaptic knob, inside which are numerous mitochondria and vesicles packed with a substance called a neurotransmitter which at the time of nerve impulse conduction diffuse across the space and bind to receptors in the membrane of the postsynaptic cell. This opens ion channels in the postsynaptic membrane resulting in a change in its membrane potential and in the consequent generation of a nerve impulse.