The Nervous System
The nervous system helps you sense the world around you. It includes the brain and the nerves as well as the senses.
The nervous system can sense changes inside and outside the body through specialized cells called receptors. This information, in the form of small electric currents, is analyzed and responses are generated in the nervous system. These responses, again in the form of small electric currents, are conveyed to the appropriate organs such as muscles or glands, at a great speed.
Your five senses are: smell (with your nose), taste (with your tongue), touch (with your fingers, and so on), sight (with your eyes), and hearing (with your ears).
If human beings couldn't smell, they wouldn't know if their food had a bad odor. If they couldn't taste either, they might like to eat everything, or, also bad in a different way, they might not like to eat anything. If they couldn't see, it would be harder for them to find their way around and avoid danger. And if they couldn't hear, they could not communicate with each other as easily.