What is the nervous system ?

The nervous system is the complex network of miilions of cells and nerves that carry messages from and to the brain and spinal cord to different various parts of body.

If your hand accidentally touches the hot lid of a vessel, what is your reaction ? You withdraw your hand immediately. This instant reaction without any thinking on your part is brought about by the nervous system. The nervous system is made up of special cells called neurons or nerve cells.

The nervous system helps us to react to our surroundings. It also helps us to think, learn and remember things.

The human brain is the body's control centre. It weighs about 1.4 kg approx.only.

The nervous system consists of three main parts. They are :

• The sense organs
• The nerves
• The brain
• Spinal cord

The sense organs are able to detect the change and send messages immediately to the brain and spinal cord along the nerves.

So, sense organs, nerves, brain and spinal cord are the main parts of the nervous system.

While thinking about nervous system, we always also think what is the main job of nervous system ? So, functions of the nervous system are as follows:

• The nervous system helps us to react to our surroundings.
• It helps us to think, learn and remember things.
• It send messages immediately to and from the brain and spinal cord along the nerves.
• It controls our body movement.
• Helps us to store information in our head.
• Carry messages from the sense organs to the brain helping us to see, hear, smell and taste.

The main part of nervous system, human brain has three parts:

• Cerebrum
• Cerebellum
• Medulla

Man is the most intelligent animal on the Earth. What makes him stand apart from all organisms is his highly developed brain. It keeps the body working smoothly and looks after thoughts, feelings and memory. The brain helps man to get messages, take decisions and send messages.

• It controls our body movement.
• Helps us to store information in our heads.

Cerebrum is the largest part of the brain. It receives signals from the sense organs and tells us what to do. It is also responsible for learning, memory, intelligence and various emotions such as joy, sorrow, etc.

Cerebellum lies below the cerebrum. It is responsible for co-ordination of movement and for maintaining the balance of our body while walking, running, dancing, etc.

An instant reaction (automatic) shown by the body to protect oneself from injury is known as reflex action .

A true reflex action is an automatic response over which the individual has no control. We are quite unconscious of most of our reflex actions.

Medulla connects the brain to the spinal cord. It controls certain vital involuntary or reflex actions such as breathing, heart beat, digestion, sneezing, etc.

The spinal cord is a thick cord or nerve tissue. It is protected by the backbone. The spinal cord transfers the information between the brain and the rest of the body. Sometimes, it even controls the actions that do not involve the brain. Such actions are called spinal reflexes.

We are aware of some reflexes such as the quick closure of eyelids when something touches it, recovery of balance after a slip. However, movement of food in intestines, change in heart beat and respiration are reflex actions we are not aware of.

There are three different kinds of nerves running throughout the nervous system of our body.

• Motor nerves
• Sensory nerves
• Mixed nerves

Carry messages from the brain to the muscles and glands resulting in movement of muscles or secretion by glands is the main work of 'motor nerves'.

Sensory nerves mainly carry messages from the sense organs to the brain helping us to see, hear, smell and taste.

Do both the functions.

1. Carry messages from our body parts .
2. And bring 'orders' from the brain or spinal cord.

One of the major part of the nervous system, major part of sensory nerves, the sense organs are like our windows to the outside world. Without them, our life would have been very dull.

Did you know the story of Hellen Keller ?She was blind and deaf since birth. Ye she managed to achieve so much in her life. To find more about her, Click here.

4.1 Eyes

• Eyes help us to see various objects in our surroundings. The eye is the organ of sight. Common defects of the eyes are shortsightedness (myopia) and longsightedness (hypermetropia) which can be corrected using spectacles.
• Eyebrows prevent sweat from running into the eyes.
• Eyelashes protect the eyes from dirt and strong light.
• The eyelids protect the eyes from injury.

These are the sense organs which help us to hear sound around us.

Ears also help us to keep our balance. The ear has three major parts - outer, middle and inner. In mammals, the outer ear is just an external flap called pinna.

The nose helps us to smell variety of objects from fragrant perfumes to stinking drains. The inner side is lined with small hair which act as filters trapping dust particles from entering in.

The senses os smell and taste are closely linked. When we are down with a cold, the nerve endings get blocked. This is why we cannot smell things properly nor can we taste our food well.

The tongue helps us in tasting things. The tongue has thousands of tiny taste buds on it. This is why it feels rough.

Different areas of the tongue help us in tasting different kinds of substances. There are four basic tastes:

• Sweet.
• Sour
• Bitter
• Salty

It is the largest and outermost sense organ in the nervous system of our body and is water-proof. It has millions of tiny nerve endings. The nerve endings help us to feel the sensations of pain, heat, cold, pressure, etc.

The skin protects the internal organs against infection, injury and harmful sun rays. The skin also has millions of tiny holes called pores. It is through the pores that sweat is excreted.

Sweat is a waste product containing mainly of water along with the dissolved salts. Sweating brings down the temperature of our body. The salt from the sweat collects on our skin while the water evaporates. The salt can be removed by bathing regularly.

1. The nervous system consists of three important parts:

(a) The brain (b) The spinal cord (c) The nerves (d) Sense organs

2. The brain helps human being to think and take intelligent decisions. It is control centre of the body. It has three regions, the cerebrum, the cerebellum and the medulla.

3. There are three kinds of nerves : sensory nerves, motor nerves and mixed nerves.

4. Our eyes, ears, nose, tongue and skin help us to connect with the outside world.

5. The are our sense organs.

6. We must look after our sense organs.