The Sense Organs

• Diagram of the Ear

  
• The pinnacle is the outer visible ear and funnels sound into the ear canal.
• The ear canal is the tube leading to the eardrum. It has hair to trap dirt and germs.
• The eardrum is the membrane of skin that vibrates when sound waves hit it.
• The middle ear contains three small bones and the Eustachian tube.
• The ossicles are three small bones called the hammer, anvil and sitirrup that amplify the sound.
• The Eustachian tube keeps air pressure equal on each side of the ear drum.
• The cochlea contains nerves that convert sound vibrations into electrical impulses.
• The semi-circular canals help us keep our balance and posture.
• Deafness can be caused by long exposure to a high level of noise, drugs, or ear infections. 
• Diagram of the Eye

  
• Eyelids cover and protect the eyes.
• The conjunctiva is a thin and transparent lining protecting the cornea.
• The cornea is the transparent layer at the front of the eye that focuses light rays on the retina.
• The sclera is a tough fibrous layer that maintains the shape of the eye.
• The choroid contains blood vessels supplying food and oxygen to the cells of the eye. 
• The retina is the innermost layer that contains the receptor cells (rods and cones).
• Rods detect black and white and are found all over the retina. Cones detect colors and are found at the fovea.
• The iris contains blood vessels and melanin and controls the amount of light entering the eye through the pupil.
• The aqueous humor is a watery liquid that supplies the lens and cornea with nutrients and helps keep the shape of the cornea and lens.
• The blind spot is where the optic nerve fibers pass through the retina and there is no room for receptors. 
• The ciliary muscle is a thickened edge of the choroid that controls the shape of the lens 
• Suspensory ligaments hold the lens in place.
• The lens focuses light rays on the retina.
• For close vision, the ciliary muscle contracts, the suspensory ligaments relax, the lens becomes thicker.
• When the eye is at rest, the lens is thin, has a long focal length and is adapted for seeing distant objects.
• Accommodation is the ability of the lens to change its shape (focal length) to form a clear image.
• You are long-sighted if you can clearly see objects a long way off, but you cannot see things close by. Convex glasses can solve this.
• Diagram of long-sightedness

  
• You are short-sighted if you can clearly see objects close to you, but you cannot see things in the distance. Concave lenses are used to fix this.
• Diagram of short-sightedness.