• 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:-
• 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.
• 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.)
• 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)
• 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.
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.