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Chapter 8 Special Senses

Chapter 8 Special Senses. The Senses. Special senses Smell Taste SIGHT Hearing Equilibrium Lady website. The Eye and Vision. Of all the sensory receptors in the body 70% are found in the eyes Optic tracts Carry information from the eyes to the brain

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Chapter 8 Special Senses

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  1. Chapter 8Special Senses

  2. The Senses • Special senses • Smell • Taste • SIGHT • Hearing • Equilibrium • Lady website

  3. The Eye and Vision • Of all the sensory receptors in the body • 70% are found in the eyes • Optic tracts • Carry information from the eyes to the brain • Consists of over a million nerve fibers per eye

  4. The Eye and Vision • Protection for the eye • Only 1/6th of the eye’s surface can be seen • Remaining portion of the eye • Enclosed in a bony orbit • Cushioned by a layer of fat • Accessory Structures • Eyelids • Conjuctiva • Extrinsic eye muscles • Lacrimal apparatus

  5. Accessory Structures of the Eye • Eyelids • Meet at the medial & lateral corners of the eye = (Medial & lateral canthus) • Nictitating membrane • Eyelashes

  6. Accessory Structures of the Eye

  7. Accessory Structures of the Eye • Conjunctiva • Delicate membrane • Lines the eyelids & covers part of the outer surface of the eyeball • Connects to the surface of the eye • Secretes mucus to lubricate the eye • Conjuctivitis?

  8. Accessory Structures of the Eye

  9. Conjunctivitis • PINKEYE • Common condition • Inflammation of the conjunctiva • Clear membrane that covers the white part of the eye & lines the inner surface of the eyelids • No danger to the eye or your vision • Causes • Bacteria, viruses, allergies (hay fever), irritants

  10. Accessory Structures of the Eye • Lacrimal apparatus • Consists of the lacrimal glands and ducts  drain lacrimal secretions into the nasal cavity • Lacrimal glands • Continually release tears • Tears • Antibodies • Lysozyme • Enzyme that destroys bacteria • Clean, protect and moisten the eye surface

  11. Accessory Structures of the Eye • Extrinsic (external) eye muscles • 6 muscles attached to the outer surface of each eye • Produce eye movements

  12. Internal Structures: The Eyeball • Eyeball • Hollow sphere • Its wall is composed of three tunics (layers) • Sclera or fibrous tunic • “White of the eye” • Outermost layer • Choroid or vascular tunic • Middle layer • Sensory tunic • Innermost layer • Retina • Interior is filled with fluids called humors

  13. Internal Structures: The Eyeball

  14. The Fibrous Tunic • Sclera • White connective tissue layer • “White of the eye” • Cornea • Transparent “window”- central anterior portion • Allows for light to pass through • Repairs itself easily • Only human tissue that can be transplanted from one person to another without the fear of rejection • No blood vessels  beyond the reach of the immune system

  15. Choroid Layer • Middle layer • Blood-rich nutritive tunic • Pigment prevents light from scattering • Modified anteriorly into two structures • Cilliary body – smooth muscle to which the lens is attached • Iris • Pigmented layer that gives eye color • Pupil – rounded opening in the iris through which light passes

  16. Sensory Tunic (Retina) • Contains receptor cells (photoreceptors) • Rods • Cones • Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve • Photoreceptors • Distributed over the entire retina, except where the optic nerve leaves the eyeball • Optic disc or blind spot*

  17. Neurons of the Retina

  18. Neurons of the Retina & Vision • Rods • Most are found towards the edges of the retina • Allow dim light vision and peripheral vision • Test fact of rod location by looking “off-center” at objects at night…stars/glow-in-the-dark objects on ceiling • Perception is in all gray tones

  19. Neurons of the Retina & Vision • Cones • Densest in the center of the retina • Fovea centralis • Area of the retina with only cones • Greatest visual acuity • 3 types of cones  respond to a particular wavelength of light • Blue light • Green light • Both green & red light • ** Color blindness  lack of one to all cone types

  20. Color-Sensitive Cones

  21. Lens • Focuses light entering the eye on the retina • Flexible biconvex crystal-like structure • Held in place by a suspensory ligament  attached to the ciliary body • Divides the eye into 2 segments • Anterior (aqueous) segment • Posterior (vitreous) segment

  22. Lens

  23. Internal Eye Chamber Fluids • Anterior (aqueous) Segment • Contains a watery fluid  Aqueous humor • Found in chamber between the lens and cornea • Similar to blood plasma • Helps maintain intraocular pressure • Provides nutrients for the lens and cornea • Reabsorbed into venous blood • Blocked drainage = Glaucoma

  24. Internal Eye Chamber Fluids • Posterior (Vitreous) Segment • Vitreous Fluid • Gel-like substance behind the lens • Keeps the eye from collapsing • Lasts a lifetime and is not replaced

  25. Lens Accommodation • Light must be focused to a point on the retina for optimal vision • Resting eye is set for distance vision (over 20 ft away) • The lens must change shape to focus for closer objects

  26. Vision • Emmetropia • Correct focus • Myopia  nearsightedness • Focus of light in front of retina • Eyeball too long or lens too strong • Distant objects are blurry • Hyperopia  farsightedness • Focus of light beyond the retina • Short eyeball or lazy lens • Near objects are blurry.

  27. Emmetropia

  28. Hyperopia

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