Question

Transmission of nerve impulses through nerve fibres are unidirectional because

• A. nerve fibres are 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 the dendrites

Answer 1

The correct option is D neurotransmitters are released by the axon endings and not by the dendrites

Nerve impulse is the signal that is transmitted in a neuron with the help of electrical signals.

It starts with receiving information in the form of chemical signal (neurotransmitters) from another neuron through the dendrites. This information is transported ahead by the axon in the form of an electrical signal to the another neuron by releasing the neurotransmitters.

Since, neurotransmitters are released by the axon terminals and not by the dendrites, the transmission of nerve impulse through the nerve fribres becomes unidirectional from dendrites to axons.

Medullary sheath contributes to the speed and not to the directionality of the nerve impulse. Sodium pumps open near the cyton first because dendrites are close to the cyton and dendrites receives the signal.