Light goes into your eye through an opening called the pupil. The iris is the colored part of the eye. Muscles attached to the iris change its shape to control how much light gets in. Your pupils get smaller in bright light and open wider in dim light. The retina is a light-sensitive layer at the very back of the eye. Cones sense color and need more light than rods, while rods work better in dim light.

Sound waves go into your ears and make your eardrums vibrate. Three tiny bones in the middle ear pass on the vibrations. The cochlea is a snail-shaped part of the inner ear. It turns vibrations into nerve signals. You may have heard that you have only five senses. In fact, you also have a sense of balance. The semicircular canals in your inner ear tell your brain when your head turns, which helps you stay balanced.

Your nose lets you smell. Special smell receptors high in the nose detect odor molecules that travel through the air. You use your tongue to taste. Food has to dissolve in saliva before you can taste it. You may have heard that you taste only with your tongue. In fact, flavor comes from taste and smell working together.

The epidermis is the top layer of your skin. Touch starts with touch receptors in your skin, which send nerve impulses to the brain. Fingers and lips have more touch receptors than your back, so they feel more. Braille is a way of reading with the fingers, using raised dots. American Sign Language is the primary language of many North Americans who are deaf or hard of hearing. It is expressed by movements of the hands and face.

Your senses send messages to your brain. Smell receptors in the nose send messages to the brain, which identifies the smell. The auditory nerve carries signals from the ear to the brain. You may think your eyes alone make the picture you see. In fact, the optic nerve carries signals from the eye to the brain.

Words to know

• iris: colored part
• retina: back of eye
• cochlea: snail-shaped part
• saliva: spit
• epidermis: top layer