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Enhancing the senses – worksheet Eye Anatomy Zonules The fiber-like processes extending from the ciliary body to the capsule of the lens of the eye. The zonules are responsible for holding the lens of the eye in its normal position. Sclera The white outer wall of the eye. Cornea The front clear "window" of the eye (where a contact lens rests). The cornea is responsible for focusing light rays to the back of the eye. 1 Retina The layer of tissue lining the inside of the back of the eye. The retina contains millions of photoreceptor cells which convert light into images. Macula The center of the retina which is responsible for about the central 15 degrees of vision. The macula is approximately 5.5mm (less than 1/4 inch) in diameter. Optic Nerve The bundled collection of the retinal nerve fiber layer which transmits visual information from the eye to the brain. Iris The colored structure which rests behind the cornea and in front of the natural lens. The opening in the center of the iris is the pupil. The iris acts like a camera shutter and controls the amount of light that enters the eye. Lens Normally clear, the lens sits behind the iris and in front of the vitreous humor. The lens focuses light rays on the back of the eye. Ciliary Body Located just behind the iris, the ciliary body is instrumental in controlling focusing of the eye and the production of aqueous fluid. Choroid A vascular layer situated between the retina and the sclera of the eye. 2 Your ears are not just for hearing — they are also important for controlling position sense and balance. Each ear is divided into 3 sections: the outer; middle; and inner ear. The middle and inner parts of the ear are located in hollow spaces on either side of the head within the temporal bones of the skull. The outer ear The external part of your ear consists of the pinna and ear lobe. The pinna is the shell-like part of your external ear, and is made of cartilage and skin. It directs sound waves from the outside into your external auditory canal (ear canal), which in turn channels sound waves to the tympanic membrane (better known as the ear drum). The tympanic membrane is a thin, semi-transparent membrane that connects the outer and middle ear. The middle ear The middle ear is an air-filled space that contains 3 tiny bones (also known as ossicles), called the malleus, incus and stapes (stirrup). Sound waves that reach the tympanic membrane cause it to vibrate. This vibration is then transmitted to the ossicles, which amplify the sound and pass on the vibration to the oval window (a thin membrane between the middle and inner ear). The Eustachian tube is a narrow tube that connects your middle ear to the back of your nose and throat. When you swallow, your Eustachian tube opens up to 3 allow air into the middle ear, so that the air pressure on either side of the tympanic membrane is the same. In situations when there is a sudden change in air pressure (e.g. during take off and landing when travelling on a plane), the pressure in the middle ear is not the same as the outside air pressure. This can make your ear drum bulge or retract and less able to transmit vibrations, causing temporary hearing problems. By swallowing or ‘popping’ your ears, you can equalise the pressure. The inner ear The inner ear (also called the labyrinth) contains 2 main structures — the cochlea, which is involved in hearing, and the vestibular system (consisting of the semicircular canals, saccule and utricle), which is responsible for maintaining balance. The cochlea is filled with fluid and contains the organ of Corti — a structure that contains thousands of specialised sensory hair cells with projections called cilia. The vibrations transmitted from the middle ear cause tiny waves to form in the inner ear fluid, which make the cilia vibrate. The hair cells then convert these vibrations into nerve impulses, or signals, which are sent via the auditory nerve to the brain, where they are interpreted as sound. The round window (fenestra cochlea) is a membrane that connects the cochlea with the middle ear. It helps dampen the vibrations in the cochlea. The semicircular canals also contain fluid and hair cells, but these hair cells are responsible for detecting movement rather than sound. When you move your head, the fluid within the semicircular canals (which sit at right angles to each other) also moves. This fluid motion is detected by the hair cells, which then send nerve impulses about the position of your head and body to the brain to allow you to maintain your balance. The utricle and saccule work in a similar way to the semicircular canals, allowing you to sense your body’s position relative to gravity and make postural adjustments as required. 4 5 SPECIAL RECEPTOR CELLS FOR EACH OF THE SENSES Vision: rod + cone Hearing Smell Taste Touch: free nerve-ending, Meissner Corpuscule Rod and cone cells in the eye respond to electromagnetic radiation—light. The ear’s receptor neurons are topped by hair bundles that move in response to vibrations— sound. Olfactory neurons at the back of the nose respond—and bind—to odorant chemicals . Taste receptor cells on the tongue and back of the mouth respond—and bind—to chemical substances. Meissner corpuscles are specialized for rapid response to touch, while free nerve endings bring sensations of pain http://library.thinkquest.org/3750/smell/smell.html http://yucky.discovery.com/flash/body/pg000150.html http://library.thinkquest.org/3750/taste/taste.html 6