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Nervous System

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Nervous System - Lesson Summary

Nervous system is the organ system present in the animals to control and coordinate different activities of the body.  Nervous system comprises of the brain, the spinal cord, and a huge network of nerves that are spread throughout the body.

The nervous system is responsible for sending, receiving and processing messages in the form of chemical signals called as impulses.

A neuron is the basic unit of the nervous system. Each neuron consists of three parts, namely, the cell body or cyton, branched projections called the dendrites, and the long process from the cell body, called the axon.

Synapse is a gap between two neurons.

Nerves are thread like structures emerging out of the brain and spinal cord. Nerves branch out to all parts of the body and are responsible of carrying messages in the body.
Types of nerves: Different types of nerves present are sensory, motor and mixed.
        •  Sensory nerves send messages from the sense organs to the brain or spinal cord.
        •  Motor nerves carry messages back from the brain or spinal cord to all the muscles and glands in the body.
        •  Mixed nerves carry both sensory and motor nerves.

Reflex action and Reflex arc
Reflex action is an involuntary action by the body. Reflex is an action generated by the body in response to the environment.

Reflex arcs are formed in the spinal cord itself, although the information input goes on to reach the brain.

Types of nervous system
The nervous system is divided into two systems – the central nervous system and the peripheral nervous system.

Central nervous system:  It includes the brain and the spinal cord. It receives information from the body and sends out instructions to particular organs.
        •  The forebrain is the main thinking part of the brain. It consists of the cerebrum and diencephalon. The cerebrum is the seat of memory and intelligence, and of sensory centres like hearing, smell and sight. The diencephalon is the seat for pressure and pain.
        •  The midbrain connects the forebrain to the hindbrain and controls the reflexes for sight and hearing.
        •  The hindbrain consists of the cerebellum, pons and medulla. The cerebellum coordinates muscular activities and maintains balance and posture. The medulla controls involuntary activities like blood pressure and beating of the heart.
        •  The spinal cord extends from the medulla of the brain through the whole length of the vertebral column and is protected by the vertebral column or backbone.

Peripheral nervous system:  It consists of the cranial and spinal nerves. The peripheral nervous system is divided into autonomic nervous system and somatic nervous system.
        •  Autonomic nervous system includes motor nerves that control involuntary actions like breathing, beating of the heart, and peristaltic movements of the alimentary canal.
        •  Somatic nervous system includes voluntary actions like muscle movement and blinking of the eyelids.

        •  The cranial nerves originate from the brain.  Some cranial nerves carry impulses to and from the central nervous system.  Some cranial nerves are mixed, while the others are sensory and motor nerves.
        •  The spinal nerves originate from the spinal cord.  All spinal nerves carry impulses to and from the central nervous system. Spinal nerves are mixed nerves.


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