1. The Central Nervous System (CNS) : It comprises of the brain and spinal cord and regulates all activities of the body.
2. The Peripheral Nervous System (PNS) : It includes all the nerves. The nerves form a network and spread throughout the body. They are instrumental in connecting all parts of the body to the central nervous system.
3. The Autonomic Nervous Sytem (ANS) : If comprises of all the nerves present in the involuntary organs like heart, stomach, lungs etc.
4. On the basis of their function, the nerves are categorized as afferent and efferent nerves.
5. The nerves are composed of neurons and neuroglia. The neurons are specialized cells capable of creating and transmitting electrochemical impulses. The neuroglia are supportive cells which assist the neurons in their function.