Introduction to Nervous System

The system that receives and transmits the stimulus, to and from the brain is called the nervous system.

Neuron:

The cell that transmits the message one part of the body to the other part is called nerve cell or neuron. A neuron is divided into three parts cell body, axon and dendrites. Cell body is the main cellular part of the neuron. All the protein synthesis occurs in cell body. Axon is the longest extension arising from thecell body. It carries electrical impulse away from the cell body. Sometimes the neuron has insulation sheet called myelin associated with it. Those neurons are called myelinated nerve cell. It increases the velocity of the impulse carried by the nerve. These type of neuron found in theperipheral nervous system. Dendrites are the short but numerous extension arising from the cell body. They carry impulse from other neurons into the cell body.

Types of Neuron:

There are three types of neuron on the basis of work performed by them. They are

1. Afferent or Sensory nerve: They carry impulses from various parts of the body to the brain or spinal cord.
2. Efferent or motor nerve: They carry impulses from the brain or spinal cord to different parts of the body. They are of three types:

• Motor nerves enter into muscle.
• Secretary nerves enter into various glands.
• Vasomotor nerves control blood vessels.

3. Mixed nerve: Sometimes axons of both motor and sensory neurons form a nerve which is called motor nerve. All the spinal nerves are mixed types.

Parts of Nervous System:

Human nervous system is divided into three parts. They are:

1. Central Nervous System (CNS): Consist of brain and spinal cord
2. Peripheral Nervous System (PNS): Consist of cranial nerves (nerves arising from brain) and peripheral nerves (nerves arising from spinal cord)
3. Autonomic nervous system (ANS): consist of ganglia and subganglia in organs.