Unit of nervous systems:

Neuron.

The correct answer is Option (1) -Neuron.

Neurons function as both the structural and functional building blocks of the nervous system, which comprises billions of these specialized cells. Also known as nerve cells, neurons play a pivotal role in receiving, processing, and transmitting information through a combination of electrical and chemical signals. They serve as the fundamental units of the nervous system, with the brain being the central organ where information undergoes processing.

A neuron is a microscopic structure composed of three major parts, namely, cell body, dendrites and axon. The cell body contains cytoplasm with typical cell organelles and certain granular bodies calledNissl’s granules. Short fibres which branch repeatedly and project out of the cell body also contain Nissl’s granules and are called dendrites. These fibres transmit impulses towards the cell body. The axon is a long fibre, the distal end of which is branched. Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called neurotransmitters.