CBSE Class 5 Science – 4. Nervous System (Notes)

Introduction

The nervous system is the body’s internal communication network.

This system carries and brings messages to and from the brain.

With these messages, we sense and respond to our environment.

This system controls different functions of our body.

 

Nervous system – The network of nerve cells and fibres which transmits nerve impulses between parts of the body is Called nervous system.

The nervous system comprises the nerves, brain and spinal cord.

They receive and integrate the signals relayed from sense organs (such as the eyes, nose, and ears).

Nerves have an important role in receiving and integrating the signals.

This system also controls unconscious functions such as heartbeat and breathing.

 

Nerves – One or more bundles of fibers forming part of a system that conveys impulses of sensation, motion, etc., between the brain or spinal cord and other parts of the body is called nerves.

Nerves are thread like structures spread throughout the body.

They carry and bring messages to and from the brain.

Nerves carry messages from the body parts through the spinal cord to the brain.

They also bring messages from the brain through the spinal cord to the body parts.

Nerves act like telephone wires which communicate the message to the brain.

Messages are sent and received through nerve cells.

 

Nerves are of different kinds

Sensory nerves – A nerve that passes impulses from receptors toward or to the central nervous system.

Sensory nerves carry a message from a body part to the brain.

These nerves allow sensing.

 

Motor nerves – A nerve carrying impulses from the brain or spinal cord to a muscle or gland is called motor nerves.

Motor nerves bring messages from the brain to the muscles.

These cause the muscles to contract.

These are responsible for the actions taken by the body.

Suppose you want to walk.

A message is sent from the brain through the motor nerve

The motor nerve in your leg carries the message to the muscles.

Your muscles receive the message and you lift your leg to walk

 

Mixed nerves – A nerve containing both sensory and motor fibers is called mixed nerves.

Mixed nerves pass signals between the sensory nerves and motor nerves.

 

Brain – An organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals is called brain.

Brain is the most important and delicate organ in the body.

It is protected by the skull, is the main control centre of the body.

The brain controls the body by receiving and giving messages.

Messages coming from different body parts tell the brain, what is needed by the body.

Messages sent by the brain tell different body parts, what to do and how to do.

The brain not only thinks, gives reason, remembers but also controls the movement body. It observes all sorts of actions done or needed by the body.

 

Parts of the Brain

Cerebrum – An enlarged anterior or upper part of the brain is called cerebrum.

The outer part of the brain is the cerebrum.

It is the largest part of the brain.

The cerebrum controls thinking, learning, intelligence, memory and talking.

It also controls the functions of sense organs.

 

Cerebellum – The portion of the brain in the back of the head between the cerebrum and the brain stem is called cerebellum 

The part below the cerebrum is the cerebellum.

The cerebellum controls the voluntary muscles of the body.

Playing, running, moving hand, riding a bike and other movements they are controlled by cerebellum.

 

Medulla oblongata – The bottom part of the brain that connects the brain to the spinal cord is called the medulla oblongata.

It controls all involuntary movements of the body.

It controls the muscles for breathing, heartbeat, digestion etc.

 

Spinal cord – A column of nerve tissue that runs from the base of the skull down the center of the back is called spinal cord.

Spinal cord is formed by a large group of nerves.

It is thick, cord like bundle of nerve cells.

Messages travel along the spinal cord, to and from the brain.

The spinal cord is like a connecting cable.

It connects the nerves to the brain.

It is well protected in the flexible but tough bony spine.

Reflex Action – An automatic (involuntary) and rapid response to a stimulus is called reflex action.

Some body movements are done automatically without thinking about them.

This automatic response of body to an event is called reflex action.

The reflex action involves only the nerves and spinal cord.

For example, your mouth gets watered at the sight of ice-creams and chocolates.

Similarly, the action, such as moving your hand away from a thorn place without the message going to the brain.

The reflex action allows fast reaction.

In reflex action, on touching the thorn or needle, the sensory nerves send a message to the spinal cord and the spinal cord orders the hand to withdraw immediately.

Sense organs – An organ of the body which responds to external stimuli by conveying impulses to the sensory nervous system is called sense organ.

 

Eyes

The eyes are our most important sense organ.

We see the beautiful world around us with the help of eyes.

The coloured circle in the eye is the iris.

The black spot in the centre of the iris is the pupil.

Light enters the eye through the pupil.

The nerve cells in the eye send messages along the optic nerve to the brain.

The brain ‘reads’ the messages and enables us to see the objects.

The front part of the eye is protected by a transparent covering called cornea.

Eyelids and eyelashes also protect the eyes.

They keep out dust and dirt.

 

Ears

We hear sounds through our ears.

The sound of an object enters the outer ear and travels through the middle and inner ear.

From there, it is sent to the brain by the nerves.

Ears also help us to keep our balance.

 

Nose

Nose helps us to smell different objects.

In External car the upper part of our nose there are endings of nerves which are sensitive to smell.

They send the message to the braid and the brain tells us what the smell is.

When we have a blocked nose, no air can reach the nerve endings and we cannot smell.

The senses of smell and taste are linked.

Our food does not taste good if we cannot smell it because of a blocked nose.

 

Tongue

We can sense four types of tastes-sweet, sour, salt and bitter.

These are sensed by means of four kinds of nerve endings in our tongue.

These are called taste buds.

These taste buds are grouped together in different regions of the tongue.

 

Skin

Skin is the protective outer covering of our body.

It contains nerve endings which detect sensation of touch, pain, heat or cold. Some parts of o skin such as finger tips, have more nerve endings than other par of the body so these are more sensitive.