The human body can do some truly awesome things. Some of these things might seem simple, like being able to see and hear the TV or smelling someone's perfume. But things like feeling the softness of a feather or tasting something sweet take a lot of work for your body to do, and yet they happen without you ever having to think about it. That's pretty amazing! Sight, touch, taste, smell, and hearing are our senses, and without them you couldn't enjoy the warm, beautiful, and sweet things in life as completely. By learning how the senses work, it's easy to see how they all work together so that people can enjoy everything about the world around them.
Each of the senses depends on a part of the body. These parts of the body are important because they send signals to the brain so that it can make sense of them. Once the brain does that, it combines the information in a way that people can understand and enjoy. For example, the sense of sight depends on the eyes. You probably already know that eyes are what people use to see, but how do they work? When a person looks at something like a flower, light bounces off of the flower and goes through the dark, center part of the eye. This is called the pupil. Behind the pupil there is a lens. The light continues to travel through the lens, which makes the picture as clear as possible and turns it upside down. That's right, upside down! The image shines on the back part of the eye called the retina. In the retina, there are sensors that are called rods and cones. These rods and cones are how people see color and darkness. The image is then turned into an electrical message that travels to the brain. It reaches the brain by traveling along what is called the optic nerves. Once it arrives, the brain turns the image right-side up again and makes sense of it so that the person can see it. This sounds very complicated, but it happens quickly and people don't even have to think about what is happening.
Touch depends on skin, which is an organ. Because it covers all of the body, it is the largest organ in the human body. There are nerve endings in skin that send signals to the brain when touched. Different nerves send the brain different information about what's being felt. Did you know that there are three layers of skin? They are called the epidermis, the dermis, and the subcutaneous fat. In the middle layer of skin, the dermis, there are nerve endings that sense heat, cold, pressure, pain, and itching. These are the nerves that signal the brain so that you'll know what something feels like.
The sense of taste is experienced with the help of the tongue. On the tongue, there are small sensors that look like little bumps. These bumps are called papillae. In these bumps are taste buds that pick up different flavors from food. Depending on the buds, they can pick up flavors like salty, sweet, sour, and bitter. Smell also helps the brain taste food! The brain uses the messages sent from the tongue and the nose when it determines taste.
So how does the nose smell things? When a person breaths in, they are pulling air into their nose. Odors, or smells that come from things such as food or perfume, are carried back into the nose where sensors detect the odor molecules that have become trapped. These sensors are called olfactory sensors and they send a message to the brain telling it what odor has been detected.
Lastly, there's hearing. Sound waves travel through the air and to the ears, where they travel through the ear canal toward the middle and inner ear. Before reaching the inner ear, the sound hits the ear drum. This is actually a thin layer of skin that vibrates when the sound waves hit it. This causes the bones behind it to vibrate and make the sound signal louder. Eventually the sound makes it to the cochlea. This is filled with liquid and hair cells and looks kind of like a snail. When the sound hits this, it causes the liquid to move. When the liquid moves, it also moves the hairs. These moving hairs send the sound information to what is called the auditory nerve. Then, the sound information travels along this nerve all the way up to the brain.