15-1 Anatomy and Physiology, Sixth Edition Lecturer: Dr. D. Fisher Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Special Senses: The ear and eye

15-2 The Ear External ear: Hearing; terminates at eardrum Middle ear: Hearing; contains auditory ossicles Inner ear: Hearing and balance; interconnecting fluid-filled tunnels and chambers

15-3 The Ear External ear –Auricle or pinna: elastic cartilage –External auditory meatus Lined with hairs and ceruminous glands –Tympanic membrane Vibrated by sound waves Middle ear –Auditory or eustachian tube Opens into pharynx, equalizes pressure Ossicles: malleus, incus, stapes: transmit vibrations Oval window

15-4 Inner Ear Labyrinth –Bony Cochlea: Hearing Vestibule: Balance Semicircular canals: Balance –Membranous -Lymphs –Endolymph In membranous labyrinth –Perilymph Space between membranous and bony labyrinth

15-5 Structure of Cochlea

15-6 Auditory Function Vibrations produce sound waves –Volume or loudness : Function of wave amplitude –Pitch: Function of wave frequency –Timbre: Resonance quality or overtones of sound

15-7 Effect of Sound Waves on Cochlear Structures

15-8 CNS Pathways for Hearing

15-9 Balance Static –Evaluates position of head relative to gravity –Detects linear acceleration and deceleration –Utricle and saccule Maculae: Consist of hairs embedded in gelatinous mass containing otoliths Kinetic –Evaluates movements of head –3 semicircular canals Ampulla –Crista ampullaris –Cupula: endolymph moves when head moves

15-10 Structure of the Macula

15-11 Vestibule in Maintaining Balance

15-12 Semicircular Canals

15-13 CNS Pathways for Balance

15-14 Ear Disorders Tinnitus –Ringing, clicking, whistling in ear due to disorders in middle or inner ear Motion sickness –Dysfunctions caused by stimulation of semicircular canals during motion Otitis Media –Infections in the middle ear Earache –Results from otitis media, dental abscesses, TMJ pain

15-15 Anatomy of the Eye Three coats or tunics –Fibrous: Consists of sclera and cornea –Vascular: Consists of choroid, ciliary body, iris –Nervous: Consists of retina

15-16 Anatomy of the Eye Fibrous tunic: Outer –Sclera: White outer layer, maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea –Cornea: Avascular, transparent, allows light to enter eye and bends and refracts light Vascular tunic: Middle –Iris: Controls light entering pupil; smooth muscle –Ciliary muscles: Control lens shape; smooth muscle Retina: Inner –Contains neurons sensitive to light –Macula lutea or fovea centralis: Area of greatest visual acuity –Optic disc: Blind spot Compartments –Anterior: Aqueous humor –Posterior: Vitreous humor Lens –Held by suspensory ligaments attached to ciliary muscles –Transparent, biconvex

15-17 Functions of the Complete Eye Eye functions like a camera Iris allows light into eye Lens, cornea, humors focus light onto retina Light striking retina is converted into action potentials relayed to brain

15-18 Light Visible light: Portion of electromagnetic spectrum detected by human eye Refraction: Bending of light –Divergence: Light striking a concave surface –Convergence: Light striking a convex surface Focal point: Point where light rays converge and cross

15-19 Focus and Accommodation Emmetropia: Normal resting condition of lens Far vision: 20 feet or more from eye Near vision: Closer than 20 feet –Accommodation –Pupil constriction –Convergence

15-20 The Retina Provides black backdrop for increasing visual acuity Sensory retina and pigmented retina Photoreceptors –Rods: Noncolor vision Rhodopsin reduction: Light adaptation Rhodopsin production: Dark adaptation –Cones: Color vision

15-21 Sensory Receptor Cells

15-22 Rhodopsin Cycle

15-23 Rod Cell Hyperpolarization

15-24 Visual Pathways

15-25 Eye Disorders Myopia: Nearsightedness –Focal point too near lens, image focused in front of retina Hyperopia: Farsightedness –Image focused behind retina Presbyopia –Degeneration of accommodation, corrected by reading glasses Astigmatism: Cornea or lens not uniformly curved Strabismus: Lack of parallelism of light paths through eyes Retinal detachment –Can result in complete blindness Glaucoma –Increased intraocular pressure by aqueous humor buildup Cataract –Clouding of lens Macular degeneration –Common in older people, loss in acute vision Diabetes –Dysfunction of peripheral circulation

15-26 Effects of Aging on the Special Senses Slight loss in ability to detect odors Decreased sense of taste Lenses of eyes lose flexibility Development of cataracts, macular degeneration, glaucoma, diabetic retinopathy Decline in visual acuity and color perception