Light goes into your eye through an opening called the pupil. The cornea is a dome-shaped clear layer at the front of the eye that bends light. The lens and the cornea work together to focus light on the retina, a light-sensitive layer at the very back of the eye. Cones are packed most densely in the center of the retina and give sharp detail and color. Each eye also has a blind spot, an area of the retina with no light-detecting receptors.

The iris is the colored part of the eye. Muscles attached to the iris change its shape to control how much light gets in, so your pupils get smaller in bright light and open wider in dim light. The retina uses special cells called rods and cones to process light. Cones sense color and need more light than rods, while rods work better in dim light. Two eyes help you judge depth, how far away things are.

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. Hair cells in the cochlea sit on the basilar membrane and ride the wave made by sound vibrations. Hair cells near the wide end of the cochlea detect higher-pitched sounds. The auditory nerve carries signals from the ear to the brain.

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. When your head moves, fluid in the semicircular canals moves tiny hair cells, which send a signal to your brain.

Smell receptors high in the nose detect odor molecules that travel through the air. Food has to dissolve in saliva before you can taste it, and once the food chemicals have dissolved, receptors on the taste buds can detect them. You may have heard that you taste only with your tongue. In fact, flavor comes from taste and smell working together.

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. You may think your eyes alone make the picture you see. In fact, the optic nerve carries signals from the eye to the brain. Your senses send messages to your brain.

Words to know

• cornea: clear front layer
• retina: back of eye
• cochlea: snail-shaped part
• lens: focuses light
• saliva: spit