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Special Senses Anatomy and Physiology Introduction Senses are classified in two major groups: A. Special – senses of smell, taste, sight, hearing, and balance B. General – touch, pressure, pain, temperature, itch, and proprioception (position of the body and its various parts) Anatomy of the Eye Adult eye is sphere – 1 inch in diameter Accessory structures: extrinsic eye muscles, eyelids, conjunctiva, lacrimal apparatus Eyes protected by eyelids Corners are: Medial canthus Lateral canthus Anatomy of the Eye Cont. Meibomian glands – sebacious glands produce oily secretions - lubricates eye Ciliary gland – modified sweat glandbetween eyelashes Conjunctiva – membrane - lines eyelid; covers part of outer surface Conjunctivitis –red eyes, irritation, Pink eye –bacteria or virus – highly contagious Anatomy of the Eye Anatomy of the Eye Cont. Lacrimal apparatus – gland and ducts drain lacrimal secretions into nasal cavity Lacrimal glands –Tears flush eyeball Lysozyme – enzyme that destroys bacteria Internal Structure of Eye Eye is hollow sphere wall composed of three tunics or coats Interior filled with fluid called humors – maintains shape of eye Tunics of Eyes 1. Sclera – outermost tunic – protection – white of eye A. cornea – transparent – light enters –no blood vessels -can be transplanted –not a tunic Tunics of the Eye cont. 2. Choroid – middle tunic – blood rich and dark pigment A. Ciliary body – smooth muscle structure – lens and iris are attached B. Iris – pigmented portion – eye color -has muscles to regulate light. C. Pupil - in iris – light passes Pupil Close Vision and Bright light – circular muscles contract and pupil constricts allowing less light in Distant Vision and Dim light – radial fibers contract enlarges pupil (dilate) allows more light in Tunics of the Eye Cont. 3. Retina – innermost tunic – contains millions of receptor cells –rods and cones Rods and cones -photoreceptors – nerve impulses transmitted to optic nerve Rods - see gray and peripheral vision Cones - allows us to see color no rods or cones on optic nerve where it leaves the eye –called blind spot or optic disk Inside View When a doctor looks at the back of your eye, here's the view: Visual problems Night blindness – vit A deficiency – deteriorates neural retina – rods Color blindness – lacks one or more cones – common red-green – sex linked trait – found on X chromosomes – most always in males Cont. Cataracts – vision is hazy – cause blindness – surgically remove lens Glaucoma – pressure within eye – build up of aqueous humor – causes pain, blindness in older people Myopia – nearsightedness – distant objects blurry – eyeball too long Emmetropia – good vision Hyperopia – farsightedness – eyeball too short – distant objects are clear - p. 283 Eye Muscles Six muscles control the movements of eye. Lateral rectus - moves eye laterally Medial rectus - moves eye medially Superior rectus - elevates eye Inferior rectus - depresses eye Inferior oblique - rotates eye Superior oblique - rotates eye Ch. 8 Day 2 The Ear – External Ear Auricle – fleshy partexternal ear Auricle opens into external auditory meatus –leads to eardrum Auricle directs sound waves toward external auditory meatus External Ear Cont. Meatus lined with hairs and ceruminous glands – EAR WAX Eardrum – called tympanic membrane – thin membrane, separates external from middle ear. Sound waves cause eardrum to vibrate. Middle Ear The middle ear contains three auditory ossicles – ear bones Malleus – hammer Incus – anvil Stapes – stirrup Eustachian tube – enables equalization of air pressure b/w outside and middle ear cavity. Changing altitude causes pain. swallow, yawn, chew, or hold nose to force air out of lungs Inner Ear Tunnels called bony labyrinth – maze – has fluid called perilymph Inner ear has three parts Cochlea – hearing Vestibule – between Cochlea & Semicircular canal Semicircular Canalbalance Steps involved in Hearing – Test Question Sound waves collected by auricle and conducted through external auditory meatus to tympanic membrane, causing vibrations Vibrating tympanic membrane causes malleus, incus, and stapes to vibrate Steps involved in hearing Cont. Vibration of stapes produces vibration in perilymph of scala vestibuli Causes vibration in cochlea Vibration detected by hair cells which induce action potential in cochlear neurons Action potentials conducted to CNS Perceived as SOUND by cerebral cortex Day 3 Taste and Smell Taste and Smell Chemoreceptors –taste and olfaction(smell) Taste buds – 10,000 on tongue – few on soft palate and cheeks Papillae – peglike– where taste buds are on tongue Four basic types – sweet, sour, bitter, salty Factors that affect taste – olfactory– congestion – temperature - texture The Tongue Dorsal surface covered with small projections, or papillae. 4 types of papillae: Fungiform Filiform Circumvallate Foliate FYI Older adults often prefer highly seasoned foods. (Why??) Mid-40s – diminished ability to taste and smell (fewer receptor cells) Half of people over 80 have poor taste and cannot smell at all. Geographic Tongue Some papillae fall off –Map-like, geographic appearance –Only symptom in most cases Sometimes painful –Sensitivity to hot and spicy foods No cure – heals by itself No known cause –Can happen to anyone! Geographic tongue Taste Buds Sweet – tip Salty – anterior sides Sour – posterior sides Bitter – back BUT… Taste Buds Cont. Only slight differences in locations of taste receptors. Most taste buds respond to two or more types of taste.
