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Externalearconsistsof3parts

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Unformatted text preview: lens in place; muscles pull or relax to change the shape of the lens so that the image focuses properly onto the retina [see vision tutorial] e. iris ­ muscle that opens/closes to let more/less light into the eye; the opening is called the pupil C. Eye problems 1. Nearsighted (myopic) a. the lens focuses the object in front of the retina b. corrected with a concave lens 2. Farsighted (hyperopic) a. lens focuses the object behind the retina b. corrected with a convex lens 3. astigmatism ­ points of light are focused as lines, leaded to blurry vision IV. HEARING A. External Ear ­ consists of 3 parts 1. the auricle, or pinna, which is constructed of cartilage; it focuses sound into the ear canal 2. the external auditory canal a. it is about one inch long by 1/2 inch in diameter b. it is skin lining has ceruminous glands, which produce cerumen (earwax) to trap foreign bodies and repel insects 3. the tympanic membrane (eardrum) a. located at the medial end of the ext. auditory canal b. it vibrates as sounds hit it B. Middle Ear (tympanic cavity) 1. it is filled with air and lined with mucus 2. there is a tube (pharyngotympanic, or auditory) that connects the middle ear with the nasopharynx 3. it contains three bones (ossicles) a. malleus (hammer) b. incus (anvil) c. stapes (st...
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