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The Special Senses

The Special Senses. A. Structure and function of the eye. sclera. Location Structure of the eye . cornea. fibrous tunic. Fibrous tunic. optic nerve. Sclera Cornea . iris. canals of Schlemm. dura mater. sclera. pupil. The Special Senses. A. Structure and function of the eye.

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The Special Senses

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  1. The Special Senses A. Structure and function of the eye sclera Location Structure of the eye cornea fibrous tunic Fibrous tunic optic nerve Sclera Cornea iris canals of Schlemm dura mater sclera pupil

  2. The Special Senses A. Structure and function of the eye choroid ciliary body 2. Structure of the eye b. Vascular tunic iris Choroid Ciliary body Iris with pupil Sphincter pupillae Dilator pupillae pupil pupil FULL CONSTRICTION FULL DILATION

  3. The Special Senses A. Structure and function of the eye retina 2. Structure of the eye c. Nervous tunic (retina) optic disk Photoreceptors (rods and cones) Photopigments Optic nerve Optic disc Fovea centralis optic nerve ora serrata

  4. The Special Senses A. Structure and function of the eye posterior chamber 2. Structure of the eye anterior chamber d. Lens e. Aqueous humor f. Vitreous humor anterior cavity posterior cavity

  5. The Special Senses A. Structure and function of the eye 3. Accessory structures lacrimal puncta lacrimal gland • Eyelids • Conjunctiva • Lacrimal apparatus • Extrinsic muscles lacrimal ducts nasolacrimal duct lacrimal caruncle superior and inferior lacrimal canals

  6. The Special Senses A. Structure and function of the eye 4. Light refraction and the accommodation reflex

  7. The Special Senses B. Age-related changes of the eye 1. External changes • Wrinkles and sags • Eyelids tend to not meet when eyes are closed • Upper eyelids tend to droop • Conjunctival changes • Fibrous tunic Sclera yellows and has transparent spots Cornea becomes more translucent and less spherical, leading to astigmatism Senile ring may form

  8. The Special Senses B. Age-related changes of the eye 2. Internal changes • Vascular tunic Retinal surface becomes uneven and fragile Less aqueous humor produced Ciliary muscles lose mass due to atrophy Iris hardens, color fades, dilator pupillae atrophies (senile miosis)

  9. The Special Senses B. Age-related changes of the eye 2. Internal changes b. Nervous tunic (retina) General decline in photoreceptors (?) Decreased total rhodopsin, regeneration rate, adaptation Less efficient removal of debris and wastes Increased atherosclerotic blood vessels c. Vitreous humor Becomes more liquid, causing light flashes Floaters More opaque

  10. The Special Senses B. Age-related changes of the eye 2. Internal changes d. Lens Yellows and becomes less transparent Increased cell growth on outside of lens e. Functional changes Altered refraction Less light reaching the retina Reduced light sensitivity Decreased central visual processing times

  11. The Special Senses C. Age-related dysfunctions of the eye 1. Presbyopia (farsightedness) • Practically universal post-40 • Results from loss of elasticity, flattening, and increased density of the lens • Loss accommodation during near vision 2. Blindness • Incidence of blindness increases with age • 16% of people 75 – 84 legally blind • Variety of causes

  12. The Special Senses C. Age-related dysfunctions of the eye 3. Glaucoma • Most serious eye problem of aging • 20% of blindness in the US • Caused by increased intraocular pressure Poor drainage of aqueous humor from anterior cavity Elevated pressure presses against retinal blood vessels Leads to degeneration of optic nerve fibers where they exit the eye “Tunnel” vision

  13. The Special Senses C. Age-related dysfunctions of the eye 3. Glaucoma • Etiology – mostly unknown • Onset • Symptomology • Treatments

  14. The Special Senses C. Age-related dysfunctions of the eye 4. Diabetic retinopathy • 7% of blindness in US (40,000 people) • Microaneurysms form in retinal capillaries • Areas of hemorrhage vs. areas of starvation • Symptomology • Treatments

  15. The Special Senses C. Age-related dysfunctions of the eye 5. Cataracts • 70% of people over 70 have some level • Cloudy (opaque) lens interfering with light passage • Causes Compression of old lens fibers by newer ones Oxidative reactions in lens proteins • Symptomology • Treatments

  16. The Special Senses C. Age-related dysfunctions of the eye 6. Age-related macular degeneration • Disease of the macula lutea (100% cone cells) • Loss of central vision (acuity and color) -- the opposite of tunnel vision • Cause • Two forms Dry (atrophy) – more common and very gradual Wet (hemorrhage) – rare and sudden e. No medical treatment

  17. The Special Senses C. Age-related dysfunctions of the eye 7. Detached retina • Retina attached to vascular pigment only at optic disc and ora serrata • Pressure exerted by vitreous humor “holds” the rest of the retina in place • As vitreous diminishes with age, detachment risk increases • Effects • Treatments

  18. The Special Senses D. Structure and function of the ear external auditory meatus • Location • Divisions temporal bone • External (outer) ear Auricle (pinna) External auditory meatus Tympanic membrane (eardrum) auricle (pinna) tympanic membrane

  19. The Special Senses D. Structure and function of the ear • Location • Divisions middle ear cavity b. Middle ear Ossicles (malleus, incus, stapes) ii. Auditory (Eustachian) tube iii. Oval and round windows incus malleus stapes oval window round window tympanic membrane

  20. The Special Senses D. Structure and function of the ear inner ear • Location • Divisions c. Internal (inner) ear Bony labyrinth Membranous labyrinth Perilymph and endolymph Cochlea (spiral organ) Vestibular apparatus semicircular ducts saccule utricle cochlea Semicircular ducts Utricle and saccule vi. Vestibulocochlear nerve

  21. The Special Senses D. Structure and function of the ear 3. Functions • Hearing b. Equilibrium

  22. The Special Senses E. Age-related changes of the ear 1. External ear • Auricles increase in size, lose flexibility • External auditory meatus becomes wider, causing skin within to become dry and brittle • Ear hairs become stiffer and grow longer • Earwax becomes drier, causing it to build-up

  23. The Special Senses E. Age-related changes of the ear 2. Middle ear • Tympanic membrane becomes thinner and less rigid • Ossicular joints ossify • Minor loss of hearing 3. Internal ear • Some degeneration of spiral organ cells, ganglion cells, and equilibrium receptor cells by age 50 • Loss of nerve fibers in vestibulocochlear nerve • Changes especially noticeable post-70 years

  24. The Special Senses F. Age-related dysfunctions of the ear 1. Presbycusis • Hearing loss as a result of aging • Loss of high-pitch (20kHz at childhood drops to 8kHz by age 65 • Post-65 there is also loss of low-range frequencies = difficult understanding speech • Interrupted pattern or rate of speech, or interference from background noises affects understanding of conversation • Environmental factors contribute significantly • Hearing loss is usually not severe

  25. The Special Senses F. Age-related dysfunctions of the ear 2. Tinnitus • Constant background ringing, hissing, whistling in one or both ears • Usually accompanied with some hearing loss • Mechanism unknown Obstruction of ear canal Middle ear infection Meningitis Hypertension d. 10% over age 65 complain of tinnitus

  26. The Special Senses F. Age-related dysfunctions of the ear 3. Deafness • Complete loss of hearing is not common • Conduction deafness vs. nerve deafness 4. Dizziness and vertigo • What’s the difference between the two? • 90% of elderly complain of one or the other • Often caused by inflammation of inner ear or vesitibulocochlear nerve • People tend to compensate by standing with feet wider apart and arms away from the body

  27. The Special Senses G. Structure and function of taste • Location of taste buds • Taste bud cells • Taste sensations • Substances must be dissolved • Sweet, salty, sour, bitter • Most of taste is olfaction

  28. The Special Senses H. Age-related changes in taste • General decrease in taste with age, thought to be due to decreased central sensation, not loss of cells • Decreased salivary secretion and volume • Fissure and furrow formation on tongue • Effects of tobacco

  29. The Special Senses I. Structure and function of smell • Slow generalized loss of olfactory cells • Loss of neurons in olfactory bulbs • Gradual decline in smell beginning in middle age, also related to decline in central processing • Smell identification increases to age 30-40 • Smell identification decreases post-60 • 70% identification between 20-40, but 5% >age 70

  30. The Special Senses J. Take home messages • Generalized loss of receptors • Eye – changes in lens, pupil size, and corneal curvature; loss of vitreous humor; adaptation time increases • Ear – loss of nerve fibers and sensory cells allows loss of hearing and balance with aging • General decline in taste and smell • Much decline attributed to decreased central processing end

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