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Question:

Unidirectional transmission of a nerve impulse through nerve fibre is due to the fact that
Nerve fibre is insulated by a medullary sheath.
Sodium pump starts operating only at the cyton and then continues into the nerve fibre.
Neurotransmitters are released by dendrites and not by axon endings.
Neurotransmitters are released by the axon endings and not by dendrites.

Nerve fibre is insulated by a medullary sheath.

Sodium pump starts operating only at the cyton and then continues into the nerve fibre.

Neurotransmitters are released by the axon endings and not by dendrites.

Neurotransmitters are released by dendrites and not by axon endings.

Solution:

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 vesicles packed with a substance called a neurotransmitter which at the time of nerve impulse conduction diffuse across space and bind to receptors in the membrane of the post-synaptic cell. This opens ion channels in the post-synaptic membrane resulting in a change in its membrane potential and in the consequent generation of a nerve impulse in one direction.