Nervous System

Did you know there are more nerve cells in our bodies than there are stars in the Milky Way? The nervous system is one of the most important systems in the human body that sends information from one part of the body to another. It is because of this system that we are able to control and coordinate our movements and actions.

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Parts of the Nervous System

It consists of two main parts.

• The Central Nervous System ( CNS)
• Peripheral Nervous System (PNS)

(Source – Wikipedia)

Central Nervous System

This system consists of the Brain and Spinal Cord. Find more about human brain in the related posts.

Peripheral Nervous System

It consists of the cranial nerves coming from the brain and the spinal nerves coming from the spine. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves in humans.

The peripheral nervous system is made of up of the Autonomic nervous system and Somatic Nervous System.  The Sympathetic nervous system and Parasympathetic nervous system fall under the autonomic nervous system.

The following figure explains the interrelation between the various nervous systems.

(Source – Wikipedia)

Nerves

A nerve is a thread like structure that comes out of the brain and the spinal cord. So these nerves branch out to all the parts of the body and are mainly responsible for carrying information and messages from part to the other. All the nerves make up the peripheral system. They carry information between the brain and spinal cord.

Types of Nerves

There are different types of nerves, according to the action they perform. They are:

• Sensory Nerves – These send messages to the brain from all the sensory organs,
• Motor Nerves – They carry messages from the brain to the muscles in the body.
• Mixed Nerves – They carry the sensory and motor nerves. They help in conducting the incoming sensory information and also the outgoing information to the muscle cells.

Based on which part the nerves connect to the Central Nervous System, they are classified as:

• Cranial Nerves – They start from the brain and carry messages from the brain to the rest of the body. Certain nerves are sensory nerves while some are mixed nerves.
• Spinal Nerves – These nerves originate from the Spinal Cord. They carry messages to and from the central nervous system. They consist of mixed nerves.

 Neurons

Nerves are made up special cells called the nerve cells or neurons. These neurons are the basic unit of the nervous system.

( Source – Wikipedia)

Three parts make up a neuron – axon, cell body and nerve endings. The cell body is the main part and has all the components of the cell such as the nucleus, mitochondria, endoplasmic reticulum etc. Axons are long cable-like projections that carry the messages along the length of the cell. These axons are covered by a protective covering called the myelin sheath. This myelin is made of fat and has a role in speeding up the transmission of messages down a long axon. Dendrites are the small branch-like projections that form connections with other neurons these dendrites can be present at both ends of the cell.

Synapse is the junction between two nerve cells. It consists of a minute gap. Impulses or messages pass by diffusion of a neurotransmitter.

Some Amazing Facts

• Neurons have high energy requirements and are bundled with blood vessels.
• There are billions of neurons in the body, about 100 billion in the brain and 13.5 million in the spinal cord.
• Axons can transmit electrical signals at a rate of 2,500 per second.

Solved Questions for You

Q: What is the gap between two nerve cells called?

Ans. Synapse

Q: How does the nervous system mechanism function?

Ans.  Broadly, the mechanism of the nervous system can be summarised as follows:

• Information is transmitted in the form of electric impulse.
• The flow of information is very quick.
• Axons and dendrites transmit information throughout the body, in a coordinated effort.