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Anatomy and Physiology, Sixth Edition

Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College

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.

Chapter 15Chapter 15

Lecture OutlineLecture Outline**

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Chapter 15

The Special Senses

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Special Senses

• Olfaction

• Taste

• Visual system

• Hearing and balance

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Olfaction• Sense of smell

– Olfactory neurons in this epithelium

• Bipolar neurons

– Olfactory hairs• Cilia which lies in mucous

• Odors– Odorants bind to

chemoreceptor molecules

– Depolarize and initiate action potentials in neurons

– Low threshold for odor detection

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Neuronal Pathways of Olfaction

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Taste

• Detected by taste buds• Papillae

– Vallate– Fungiform– Foliate– Filiform

• Histology– Support cells – Gustatory cells

• Hairs

• Function– Receptors on hairs

detect dissolved substances

• Taste types– Sour– Salty– Bitter– Sweet – Umami

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Papillae and Taste Buds

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Actions of Major Tastants

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Neuronal Pathways for Taste

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Visual System

• Eye • Accessory structures

– Eyebrows, eyelids, eyelashes, tear glands

– Protect eyes from sunlight and damaging particles

• Optic nerve (II) – Tracts

– Pathways

• Eyes respond to light and initiate afferent action potentials

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Accessory Structures of Eye• Eyebrows

– Prevent running perspiration into eyes

– Shade

• Eyelids or palpebrae– Consist of 5 tissue layers

– Protect and lubricate

• Conjunctiva– Covers inner eyelid and

anterior part of eye

• Lacrimal apparatus

• Extrinsic eye muscles

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Lacrimal Apparatus

• Lacrimal apparatus– Lacrimal Gland: Produces

tears to moisten, lubricate, wash

• Lacrimal Canaliculi– Collects excess tears

• Punctum

• Lacrimal Sac

• Nasolacrimal duct– Opens into nasal cavity

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Extrinsic Eye Muscles

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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

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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

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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

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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

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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

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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

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Sensory Receptor Cells

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Rhodopsin Cycle

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Rod Cell Hyperpolarization

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Visual Pathways

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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

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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

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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

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Inner Ear• Labyrinth

– Bony• Cochlea: Hearing

• Vestibule: Balance

• Semicircular canals: Balance

– Membranous

• -Lymphs– Endolymph

• In membranous labyrinth

– Perilymph• Space between

membranous and bony labyrinth

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Structure of Cochlea

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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

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Effect of Sound Waves on Cochlear Structures

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CNS Pathways for Hearing

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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

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Structure of the Macula

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Vestibule in Maintaining Balance

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Semicircular Canals

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CNS Pathways for Balance

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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

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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