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The Special Senses

The Special Senses - The Special Senses PART A Eye and...

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The Special Senses P A R T A
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Eye and Associated Structures ¡ 70% of all sensory receptors are in the  eye ¡ Most of the eye is protected by a cushion  of fat and the bony orbit ¡ Accessory structures include eyebrows,  eyelids, conjunctiva, lacrimal apparatus,  and extrinsic eye muscles
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Eyebrows ¡ Functions include: l Shading the eye l Preventing perspiration from reaching  the eye
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Palpebrae (Eyelids) ¡ Protect the eye anteriorly ¡ Palpebral fissure  – separates eyelids  ¡ Canthi  – medial and lateral angles  (commissures)
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Palpebrae (Eyelids) ¡ Lacrimal caruncle  – contains glands  that secrete a whitish, oily secretion  (Sandman’s eye sand) ¡ Tarsal plates of connective tissue support  the eyelids internally ¡ Eyelashes l Project from the free margin of each  eyelid l Initiate reflex blinking
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Palpebrae (Eyelids) ¡ Lubricating glands associated with the  eyelids l Meibomian glands  (modified  sebaceous glands) l Ciliary glands  lie between the hair  follicles (sweat and sebaceous glands)
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Palpebrae (Eyelids) Figure 15.1b
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Conjunctiva ¡ Transparent mucous membrane that: l Lines the eyelids as the  palpebral  conjunctiva l Covers the whites of the eyes as the  ocular or bulbar conjunctiva l Lubricates and protects the eye
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Lacrimal Apparatus ¡ Consists of the lacrimal gland and  associated ducts ¡ Lacrimal glands  secrete tears  l Located on the lateral portion of the  eye
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Lacrimal Apparatus ¡ Tears l Contain mucus, antibodies, and  lysozyme l Enter the eye via superolateral  excretory ducts   l Exit the eye medially via the  lacrimal  punctum l Drain into  lacrimal canaliculus lacrimal sac  and then into the  nasolacrimal duct
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Lacrimal Apparatus Figure 15.2
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Extrinsic Eye Muscles ¡ Six extrinsic eye muscles l Enable the eye to follow moving  objects l Maintain the shape of the eyeball
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Structure of the Eyeball ¡ A slightly irregular hollow sphere with  anterior and posterior poles ¡ The wall is composed of three tunics –  fibrous, vascular, and sensory ¡ The internal cavity is filled with fluids  called humors ¡ The lens separates the internal cavity  into anterior and posterior segments
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Structure of the Eyeball Figure 15.4a
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Fibrous Tunic ¡ Forms the outermost coat of the eye and  is composed of:  l Opaque sclera (posteriorly) l Clear cornea (anteriorly) ¡ The sclera protects the eye and anchors  extrinsic muscles ¡ The cornea lets light enter the eye 
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Vascular Tunic or Uvea ¡ Has three regions: choroid, ciliary body,  and iris ¡ Choroid region l A dark brown membrane that forms  the posterior portion of the uvea l Supplies blood to all eye tunics
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Vascular Tunic or Uvea ¡ Ciliary body l A thickened ring of tissue surrounding  the lens l Composed of the 
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