Nervous System

The nervous system is composed of specialized tissues, called nervous tissue. The nerve cell or neuron is the functional unit of the nervous system. It is the nervous system which is mainly responsible for control and coordination in complex animals.

Importance of control and coordination

A living being does not live in isolation. It has to constantly interact with its external environment and has to respond properly for its survival.

For example, when a hungry lion spots a deer, the lion has to quickly make a move so that it can have its food. On the other hand, the deer needs to quickly make a move to run for its life.

The responses which a living being makes in relation to external stimuli are controlled and coordinated by a system, especially in complex animals.

Neuron

Neuron is a highly specialized cell which is responsible for transmission of nerve impulses. The neuron consists of the following parts:

Fig: Neuron

1. Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hair-like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
2. Axon: This is the tail of the neuron. It ends in several hair-like structures, called axon terminals. The axon terminals relay nerve impulses.
3. Myelin Sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve impulses from the surroundings. It works in the same way as plastic casing of an electric cable.

Types of Neuron

1. Sensory neuron: These neurons receive signals from a sense organ.
2. Motor neuron: These neurons send signals to a muscle or a gland.
3. Association neuron: These neurons relay the signals between sensory neuron and motor neuron.

Human Nervous System

The nervous system in humans can be divided into two main parts, viz. the central nervous system and the peripheral nervous system. The peripheral nervous system can be further divided into the somatic nervous system and the autonomous nervous system.

Central Nervous System

The central nervous system is composed of the brain and the spinal cord. The brain controls all the functions in the human body. The spinal cord works as the relay channel for signals between the brain and the peripheral nervous system.

Peripheral Nervous System

The peripheral nervous system is composed of the cranial nerves and spinal nerves.

• There are 12 pairs of cranial nerves. The cranial nerves come out of the brain and go to the organs in the head region.
• There are 31 pairs of spinal nerves. The spinal nerves come out of the spinal cord and go to the organs which are below the head region.

Peripheral nervous system is composed of two parts. They are: somatic nervous system and autonomous nervous system.

Somatic Nervous System

This is the part of the peripheral nervous system. Somatic nervous system is associated with volunatry control of organs.

Autonomous Nervous System

The autonomous nervous system is composed of a chain of nerve ganglion which runs along the spinal cord. It controls all the involuntary actions in the human body. The autonomous nervous system can be divided into two parts:

1. Sympathetic Nervous System: This part of the autonomous nervous system heightens the activity of an organ as per the need. For example, during running, there is an increased demand for oxygen by the body. This is fulfilled by an increased breathing rate and increased heart rate. In this case, the sympathetic nervous system works to increase the breathing rate and the heart rate.
2. Parasympathetic Nervous System: This part of the autonomous nervous system slows down the activity of an organ and thus has a calming effect. During sleep, the breathing rate slows down and so does the heart rate. This is facilitated by the parasympathetic nervous system. It can be said that the parasympathetic nervous system helps in conservation of energy.

Summary

Neuron: Functional unit of nervous system. It is composed of a cell body and a tail.

Nervous System: It is composed of Central Nervous System and Peripheral Nervous System. Peripheral Nervous System is further divided into somatic nervous system and autonomous nervous system.