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Eyebrows and Eyelids

Eyebrows and Eyelids. Eyebrows facial expression, protection from glare & perspiration Eyelids (palpebrae) block foreign objects, help with sleep, blinks moisten meet at corners (commissures) lined by conjunctiva tarsal glands secrete oil that reduces tear evaporation

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Eyebrows and Eyelids

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  1. Eyebrows and Eyelids • Eyebrows • facial expression, protection from glare & perspiration • Eyelids (palpebrae) • block foreign objects, help with sleep, blinks moisten • meet at corners (commissures) • lined by conjunctiva • tarsal glands secrete oil that reduces tear evaporation • eyelashes protect eye from debris

  2. Conjunctiva • Transparent mucous membrane lines the eyelids and covers anterior surface of eyeball except cornea • Richly innervated & vascular

  3. Lacrimal Apparatus • Tears flowing across eyeball helps wash away foreign particles, help with diffusion of O2 & CO2 and contain bactericidal enzyme

  4. Eye Tunics • Fibrous = sclera and cornea (blue) • Vascular = choroid, ciliary body & iris (pink) • Nervous = retina (yellow)

  5. Aqueous Humor

  6. Ophthalmoscopic Examination of Eye

  7. Effects of Corrected Lenses • Hyperopia is farsighted (eyeball too short) • correct with convex lenses • Myopia is nearsighted (eyeball too long) • correct with concave lenses

  8. Retinal Cells • Pigmented retina • absorbs stray light & prevents reflections • Rod cells (night vision) • outer segment is stack of coinlike membranous discs studded with rhodopsin pigment molecules • Cone cells (color vision in bright light) • outer segment tapers to a point

  9. Nonreceptor Retinal Cells • Bipolar cells (1st order neurons) • synapse on ganglion cells • large amount of convergence • Ganglion cells (2nd order neurons) • axons of these form optic nerve • more convergence occurs (114 receptors to one optic nerve fiber • Horizontal & amacrine cells form connections between other cells • enhance perception of contrast, edges of objects & changes in light intensity

  10. Location of Visual Pigments Vitamin A derivative Rods have rhodopsin for visual pigment Cones have photopsin

  11. Visual Pigments • Visual pigment of the rod cells is called rhodopsin • 2 major parts to the molecule • protein called opsin • vitamin A derivative called retinal • Rod cells contain single kind of rhodopsin • Cones contain photopsin

  12. The Photochemical Reaction • In light rhodopsin is converted from the bent shape (cis-retinal) to the straight (trans-retinal) form as it is bleached • Takes 5 minutes to regenerate 50% of rhodopsin

  13. Scotopic System (Night Vision) • Sensitivity of rods in dim light • extensive neuronal convergence • 600 rods converge on 1 bipolar cell • many bipolar converge on each ganglion cell • high degree of spatial summation but no ability to resolve detail • producing only a coarse image • Edges of retina with widely spaced rod cells is low-resolution system only alerting us to motion

  14. Photopic System (Day Vision) • Fovea contains only 4000 tiny cone cells and no rods • no neuronal convergence • each foveal cone cell has “private line to the brain” • High-resolution vision

  15. Visual Projection Pathway

  16. Anatomy of Middle Ear Plus: Ceruminous glands, stapedius, oval window.

  17. vestibular apparatus cochlea Inner Ear • Passageways in temporal bone = bony labyrinth • Endolymph-filled tubes floating in perilymph inside the bony labyrinth = membranous labyrinth endolymphatic sac

  18. Anatomy of the Cochlea 2.5 coils • Stereocilia of hair cells attached to tectorial membrane. 3 fluid-filled chambers Organ of Corti

  19. Potassium Gates of Cochlear Hair Cells • Stereocilia of OHCs have tip embedded in tectorial membrane which is anchored • Movement of basilar membrane bends stereocilia • Bending pulls on tip links and opens ion channels • K+ flows in -- depolarizing it & causing release of neurotransmitter stimulating sensory dendrites at its base

  20. Frequency Response of Basilar Membrane Peak amplitude of wave varies with frequency

  21. Equilibrium • Control of coordination and balance • Receptors in vestibular apparatus • semicircular ducts contain crista • saccule & utricle contain macula • Static equilibrium is perception of head orientation • perceived by macula • Dynamic equilibrium is perception of motion or acceleration • linear acceleration perceived by macula • angular acceleration perceived by crista

  22. Saccule and Utricle • Saccule & utricle chambers containing macula • patch of hair cells with their stereocilia & one kinocilium buried in a gelatinous otolithic membrane weighted with granules called otoliths • otoliths add to the density & inertia and enhance the sense of gravity and motion Otoliths

  23. Saccule and Utricle • With the head erect, stimulation is minimal, but when the head is tilted, weight of membrane bends the stereocilia (static equilibrium) • When car begins to move at green light, linear acceleration is detected since heavy otolith lags behind (one type of dynamic equilibrium)

  24. Crista Ampullaris of Semicircular Ducts • Crista ampullaris consists of hair cells buried in a mound of gelatinous membrane (one in each duct) • Orientation of ducts causes different ducts to be stimulated by rotation in different planes

  25. Smell • Receptor cells for olfaction form olfactory mucosa • smell is highly sensitive (women > men) • distinguish as many as 10,000 odors • Covers 5cm2 of superior concha & nasal septum

  26. Olfactory Epithelial Cells • Olfactory cells • neurons with ~20 cilia called olfactory hairs • binding sites for odor molecules in thin layer of mucus • axons pass through cribriform plate • survive 60 days • Supporting cells • Basal cells

  27. Olfactory Projection Pathways

  28. Taste • Gustation is the sensation of taste resulting from the action of chemicals on the taste buds • Lingual papillae • filiform • most abundant • fungiform • at tips & sides of tongue • circumvallate • contains 1/2 of taste buds

  29. Taste Bud Structure • Lemon-shaped groups of 3 kinds of cells • taste cells, supporting cells, and basal cells • taste cells have receptors on apical microvilli

  30. Physiology of Taste • To be tasted, molecules must dissolve in saliva • 5 primary sensations: salty, _______, _______, bitter & umami • Taste is also influenced by food texture, aroma, temperature, and appearance. • hot pepper stimulates free nerve endings (pain) • Taste bud distributions

  31. Pain • Fast vs Slow Pain • Referred Pain • Visceral pain “thought” to come from skin • Pain Modulation • Analgesic chemicals • Spinal gating

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