Question

Which of the following is the pathway that a nerve impulse travels through a neuron?
A. Axon → cell body → dendrite
B. cell body → axon → dendrite
C. Axon → myelin sheath → dendrite
D. Dendrite → cell body → axon

Answer 1

A nerve is a collection of nerve cells and each nerve cell carrying a message is called a neuron. A neuron is either sensory or motor in function. The message relayed between two neurons is a nerve impulse and they travel very fast.

Complete answer:
A nerve cell is composed of three parts viz., cell body, several dendrites and an axon. The cell body contains a nucleus and a few organelles. The periphery of the cell body gives off many radiating dendrites and only one axon. The number of dendrites may vary from a few to several in a neuron. The axon is wrapped by a fatty layer called myelin sheath which provides insulation to the axon and helps in efficient transmission of electrical signals. The myelin sheath is absent at various points on an axon. These intermittent gaps are called nodes of Ranvier and they allow faster transmission of an impulse.
The junction where an axon of a neuron meets the dendrite of an adjacent neuron is called synapse. A slight gap present at the synapse is called a synaptic cleft. During the transmission of an impulse, the axon of one neuron releases signalling chemicals called neurotransmitters which pass through the synapse and are received by the dendrite of another neuron. As the neurotransmitter binds to the membrane of the receiving neuron, a nerve impulse is generated. This impulse then travels through the cell body to the axon which transmits it to the next neuron. Therefore, the pathway of a nerve impulse through a neuron is first a dendrite then the cell body and finally the axon.

So, the correct answer is option (D), Dendrite → cell body → axon.

Note:
On sensing a stimulus, the sensory receptors communicate with sensory neurons which then carry impulses to the CNS. The CNS in turn transmits the information to a motor neuron. The motor neuron then carries impulses to the effector organs.