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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:Special Senses:
The ear and eyeThe 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