As humans, we have five tools that help us explore the world around us - sight, hearing, smell, taste, and touch. Our eyes, ears, nose, mouth, and skin gather a lot of information about the world; they help protect us and help us enjoy life! Not everyone is born with all of these senses. Some people are born blind, or without being able to hear. Usually they learn to use the senses they do have better than people who have all five senses. A person who is blind may have an extra-good sense of hearing, for example. Some people also lose their sight or hearing as they get older.
Our vision is the strongest sense. As soon as you open your eyes every morning, you can see the things around you. You can watch a movie, or see a beautiful sunset, or run and play outside because of your eyes. How do our eyes work? We see color and movement because light enters our eyes and forms a pattern.
The little dark circle in the center of each of your eyes lets light in. It is called a pupil. If you are in a dark place where no lights at all are on, can you see anything? No, you can't, because our eyes need light to be able to see! Once the light goes in, it hits a part inside at the back of your eye that is very sensitive to light. This part is called the retina. When light hits the retina, it makes an upside-down picture of whatever you are looking at. The picture is sent to the brain through the optic nerve. Nerves are tiny parts in your body that act as messengers.They send signals to your brain of what they can feel, or sense. Together, the many parts inside our body that sense what is around us are called the nervous system.
When the brain receives the picture from your eyes it gets turned around very quickly so that you see it the right way instead of upside-down! This happens automatically whenever your eyes are open. Seeing is like breathing; you don't even have to think about it, but you do it all the time!
If you look at your eyes in a mirror, you will see eyelids and eyelashes which protect your eyes by keeping dust out. Every time you blink (about once every six seconds) your eye is working to keep out bits of dirt and dust so tiny you can't even see them.
Another important sense is hearing. Our ears allow us to enjoy things like being outside, talking with our friends, and listening to music. Being able to hear also helps protect us from danger, for example, we can hear if a car is coming when we are crossing the street. A human with normal hearing can tell the difference between 1500 sounds! Our brain is able to pick out really high sounds and really low sounds. If you have a piano or keyboard, try playing the lowest note, and then the highest. The piano has 88 sounds - our ears are able to pick up a much wider range of sounds, from soft to loud, low and high. We are able to hear the chirping of an insect on a summer's day, and the clashing of cymbals at a band concert.
Sound is caused when objects vibrate (move back and forth very quickly). Vibrations create sound waves that can travel in all different directions through air, water, and lots of other materials. When sound waves are spread out, the sound we can hear is quiet. When they are clumped together, the sound is much louder. When sound waves go into your ear, they hit your eardrum and make it vibrate. The tiny vibrations move through your ear like a light shining through a long tunnel until they get to some nerves at the end of your ear. The nerves take them to your brain where they turn into the sound that you hear!
What are some of your favorite smells? Without our noses we couldn't enjoy things like our favorite meal cooking, or a bouquet of flowers. Our nose also helps us know what we are eating. This happens because as we chew our food, air is flowing from our mouth to the back of our throat. When it reaches our throat, some air reaches the back of our nose. Our nose picks up the smell, and the signals are sent to the brain. The full flavor (whether you like the food or not) is "tasted" by your nose as well as your mouth!
Our tongue can pick out four types of tastes - bitter, sour, sweet, and salty. We can taste because of the tiny bumps called taste buds that are all over our tongue, and the top (or roof) of our mouth. Taste buds are connected to nerves in the tongue, and they pick up the signals that are sent to the brain so you can taste what you are eating. The inside of our mouth can also feel the foods we are eating, so if you don't like a food, it might not be the flavor, but the texture that "tastes" gross.
Our skin is very sensitive to what it comes in contact with. All over our skin are tiny receptors that are connected to nerves. These receptors are spread all over our body, allowing us to feel, but there are more receptors on our hands and face then anywhere else. Our hands are able to act like a second pair of eyes, providing a detailed picture for the brain. Our sense of touch is important in many ways. One way it protects us is by setting off reflexes. Have you ever tried to grab something that was really hot, and then quickly let go? Your senses told your body it was hot, and you reacted very quickly, even before your brain realized it felt hot. Our sense of touch allows us to enjoy things like petting a cat or dog, and running through the sprinkler on a hot day.