Nervous system


•      The nervous system controls the different organs of our body.

•      The brain is the control centre of entire body.

•      It may also be called the human computer.

•      The brain not only controls what we think and feel, but also how we learn and remember, and the way we move and talk.

Figure 27: Nervous system

•      The brain controls many other things such as the beating of heart, the digestion of food, and yes, even the stress we feel.

Figure 28: Human brain

•      If we think of the brain as a central computer that controls all bodily functions, then the nervous system is like a network that relays messages back and forth from the brain to different parts of the body.

•      It does this via the spinal cord, which runs from the brain down through the back and contains threadlike nerves that branch out to every organ and body part.

•      Both the brain and the spinal cord are protected by bones:-



•      The brain controls just about everything we do, even when we're asleep.

•      It controls our body movements and helps us to store information in our memory.

•      Our brain has three different parts that work together.


•      The biggest part of the brain is the cerebrum.

•      The cerebrum makes up 85% of the brain's weight.

•      The cerebrum is the thinking part of the brain and it controls our voluntary muscles - the ones that move.

Figure 29: Cerebrum

•      It is the largest part of the human brain and is responsible for:-

        a.  Learning

        b.  Memory 

        c.  Intelligence 

        d.  Logic



•      The cerebellum is at the back of the brain, below the cerebrum.

•      It's a lot smaller than the cerebrum at only 1/8 of its size.

•      But it's a very important part of the brain.

Figure 29: Cerebellum

•      It controls- balance, movement, and coordination (how our muscles work together).

•      Because of our cerebellum, we can stand upright, keep our balance, and move around.



•      The brain stem is located beneath the cerebrum and in front of the cerebellum.

•      It connects the rest of the brain to the spinal cord, which runs down our neck and back.

•      The brain stem is in charge of all the functions of our body which are needed to be alive, like breathing air, digesting food, and circulating blood.

Figure 30: Medulla (Brainstem)

•      Part of the brain stem's job is to control our involuntary muscles.

•      It controls activities such as heartbeat, breathing, swallowing, and sneezing.


Spinal Cord:

•      The spinal cord is a thick cord of nerve tissue, which extends down from the brain stem.

•      It is surrounded and protected by the backbone.

Figure 31: Spinal cord

•      The spinal cord is responsible for the transfer of information between the brain and the rest of the body.

•      It even controls the actions that do not involve the brain.

•      Such actions are called reflex actions.



•      A network of nerves runs throughout our body.

•      The messages travel from nerve cells all over the body.

•      They travel along nerve fibres to nerve cells in the brain.

Figure 32: Nerves

•      Sensory nerves pass through the spinal cord and carry messages to the brain.

•      Sensory nerves collect the information and send it to the brain along with the network.

•      Motor nerves carry messages back from the brain.

•      Motor nerves take the brain’s orders back along another network (like cars travelling along their own side of the highway.)


Reflex Actions:

•      The automatic response of the body to an event is called a reflex action.

•      A reflex is an involuntary action that our body does in response to something.

Figure 33: Reflex action

•      Reflex actions are due to messages sent by the spinal cord. (the brain is not involved)


Sense Organs:

•      Our brain collects all the information, sorts it out, thinks, remembers, creates, compares, solves problems and coordinates actions all at the same time - even when we’re asleep.

•      The brain senses some organs and these organs help us to see, hear, taste, smell, and touch.

•      These organs are skin, eyes, ears, nose, and tongue.



•      There are tiny nerve endings in our skin.

•      These nerve endings help us to feel things.

•      The skin contains more than 4 million sensory receptors — mostly present in the fingers, tongue, and lips.

Figure 34: (a) fingers  (b) lips  (c) tongue

•      They gather information related to touch, pressure, temperature, and pain and send it to the brain for processing and reaction.

Figure 35: Sensory receptors respond to stimulus

•      They also help us to detect heat, cold, and pain.



•      Eyes help us in seeing the various objects around us.

•      Since eyes are very important organs, our body has several features to protect them.


(a)                                   (b)

Figure 36: (a) eyes (b) several features of an eye of a boy

•      The eyebrows prevent sweat from running into the eyes.

•      The eyelashes protect the eyes from dirt and strong light.

•      The eyelids protect the eyes from injury. 



•      Ears help us in hearing.

Figure 37: Human ear

•      Every sound we hear is the result of sound waves entering our ears and causing our eardrums to vibrate.

•      They also help us to keep our balance.



•      Nose helps us to smell a variety of objects—from flowers and perfumes to rotten eggs.

Figure 38: Human nose

•      According to experts, one can distinguish between more than 10,000 different smells.



•      The tongue contains small groups of sensory cells called taste buds that react to chemicals in foods.

•      Taste buds react to sweet, sour, salty, and bitter.

Figure 39: Human tongue

•      Different regions of the tongue help us in tasting different kinds of substances.