Question

Name the structural and functional unit of the nervous system. Describe its structure.

Answer 1

Neuron

1. Neurons are the basic structural and functional units of the nervous system. It helps in relaying messages in the form of electrical impulses between sensory organs, the central nervous system, and the effector organs.
2. Neurons are of three types based on the function they perform. Sensory or receptor neurons transmit messages from the sensory receptors to the spinal cord or the brain. The motor or effector neurons transmit messages from the brain or spinal cord to the effector organs, tissues, or glands.
3. The neuron consists of different parts as shown in the diagram below. They are- a cell body (cyton) consisting of a nucleus, dendrites, axon with or without myelin sheath, nerve endings, and synapse.

Parts of the neuron

1. The cell body or cyton houses the nucleus, mitochondria, ribosomes, and other cellular structures. They are unable to undergo cell division.
2. Axon is a long cellular process that carries the nerve impulses away from the cell body.
3. Dendrites are short, highly branched cellular processes that carry the nerve impulses towards the cell body.
4. Neurons have protective insulation called neurilemma. The presence of a thin fatty sheath around nerve fibers is called the myelin sheath and such fibers are called myelinated fibers. They are present in a discontinuous fashion leaving gaps called the nodes of Ranvier.
5. The axon of the neuron terminates as swollen knob-like structures which store neurotransmitters like acetylcholine. They are closely placed near the effector cell leaving a small gap. This is called the synapse.