The Greeks believed that all functions of the body were controlled by the brain since damage to that organ produced remarkable changes in behaviour. They had very little idea on how such control could be exercised Though Galen, a Greek physiologist (A.D. 129-200) made one notable observation. One of his patients, having suffered a blow on the neck when falling from his chariot, complained loss of feeling in the arm while still retaining normal muscular control of its moment. Galen concluded that nerves were of two kinds - those of sensation and those of action.
According to him the blow in the neck had damaged the nerves of sensation but had not affected it's action.

Why do you think Galen draw such a conclusion?
The functioning of nerves as integrating systems was little known till late 18th century. Then, physiologists began to study the mechanism of nerve functioning and found how signals were transmitted by making the connection between recent work on electricity and the propositions on working of the nervous system made till then.
Now we know more about how nerves from different sections of the brain and spinal cord control responses of different areas of the body. We also know the probable pathways that transmit information but we still know very little about the working mechanisms of the nerve cell.

Observe the permanent slide of nerve cell or neuron under microscope draw and label its parts, compare with the following diagram.
Each nerve cell consists of a cell body with a prominent nucleus. There are fine projections mainly of two types extending from the cell body of the nerve cell. The small projections are dendrites while a long one that extends to different parts of our body is called Axon. The axon is surrounded by a specialized insulatory sheath called myelin sheath.This sheath is interrupted at regular intervals called nodes of ranvier.The myelin sheath is made up of schwann cells and chiefly consists of fatty material. Axons not having the sheath are non-myelinated