Vision - of the hairs initiate a reflex action that closes...

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Vision The eye is supported by the following accessory organs:  •   The eyebrows shade the eyes and help keep perspiration that accumulates on the forehead from  running into the eyes. •   The eyelids (palpebrae) lubricate, protect, and shade the eyeballs. Contraction of the levator  palpebrae superioris muscle raises the upper eyelid. Each eyelid is supported internally by a layer of  connective tissue, the tarsal plate. Tarsal (Meibomian) glands embedded in the tarsal plate produce  secretions that prevent the upper and lower eyelids from sticking together. The inner lining of the  eyelid, the conjunctiva, is a mucous membrane that produces secretions that lubricate the eyeball.  The conjunctiva continues beyond the eyelid, folding back to cover the white of the eye. •   The eyelashes, on the borders of the eyelids, help protect the eyeball. Nerve endings at the base 
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Unformatted text preview: of the hairs initiate a reflex action that closes the eyelids when the eyelashes are disturbed. • The lacrimal apparatus produces and drains tears. Tears (lacrimal fluid) are produced by the lacrimal glands, which lie above each eye (toward the lateral edge). In each eye, tears flow across the eyeball and enter two openings (lacrimal puncta) into lacrimal canals that lead to the lacrimal sac. From here, the tears drain through the nasolacrimal duct into the nasal cavity. Tears contain antibodies and lysozyme (a bacteria-destroying enzyme). • Six extrinsic eye muscles provide fine motor control for the eyeballs. These are the lateral, medial, superior, and inferior rectus muscles and the inferior and superior oblique muscles. The eyeball is a hollow sphere whose wall consists of three tunics (layers), shown in Figure 1....
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This note was uploaded on 11/10/2011 for the course PT 101 taught by Professor Staff during the Spring '10 term at Texas State.

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