Chapter 9 The Senses. Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of...

Chapter 9Chapter 9The SensesThe Senses

Elsevier items and derived items © 2008, 2004 by Mosby, Inc., an affiliate of Elsevier Inc. Slide 2

CLASSIFICATION OF SENSE ORGANSCLASSIFICATION OF SENSE ORGANS

General sense organs (Table 9-1)General sense organs (Table 9-1) Often exist as individual cells or receptor unitsOften exist as individual cells or receptor units Widely distributed throughout the bodyWidely distributed throughout the body

Special sense organs (Table 9-2)Special sense organs (Table 9-2) Large and complex organsLarge and complex organs Localized grouping of specialized receptorsLocalized grouping of specialized receptors


CLASSIFICATION OF SENSE ORGANSCLASSIFICATION OF SENSE ORGANS

Classification by presence or absence of covering Classification by presence or absence of covering capsulecapsule EncapsulatedEncapsulated Unencapsulated (“free” or “naked”)Unencapsulated (“free” or “naked”)

Classification by type of stimuli required to Classification by type of stimuli required to activate receptorsactivate receptors Photoreceptors (light)Photoreceptors (light) Chemoreceptors (chemicals)Chemoreceptors (chemicals) Pain receptors (injury)Pain receptors (injury) Thermoreceptors (temperature change)Thermoreceptors (temperature change) Mechanoreceptors (movement or deforming of capsule)Mechanoreceptors (movement or deforming of capsule) Proprioceptors (position of body parts or changes in Proprioceptors (position of body parts or changes in

muscle length or tension)muscle length or tension)


CONVERTING A STIMULUS INTO A CONVERTING A STIMULUS INTO A SENSATIONSENSATION

All sense organs have common functional All sense organs have common functional characteristicscharacteristics All are able to detect a particular stimulusAll are able to detect a particular stimulus A stimulus is converted into a nerve impulseA stimulus is converted into a nerve impulse A nerve impulse is perceived as a sensation in A nerve impulse is perceived as a sensation in

the central nervous systemthe central nervous system


GENERAL SENSE ORGANS GENERAL SENSE ORGANS (Table 9-1)(Table 9-1)

Distribution is widespread; single-cell Distribution is widespread; single-cell receptors are commonreceptors are common

Examples (Figure 9-1, Table 9-1)Examples (Figure 9-1, Table 9-1) Free nerve endings—pain, temperature, and crude Free nerve endings—pain, temperature, and crude

touchtouch Meissner’s corpuscles—fine touch and vibrationMeissner’s corpuscles—fine touch and vibration Ruffini’s corpuscles—touch and pressureRuffini’s corpuscles—touch and pressure Pacinian corpuscles—pressure and vibrationPacinian corpuscles—pressure and vibration Krause’s end-bulbs—touchKrause’s end-bulbs—touch Golgi tendon receptors—proprioceptionGolgi tendon receptors—proprioception Muscle spindles—proprioceptionMuscle spindles—proprioception


SPECIAL SENSE ORGANSSPECIAL SENSE ORGANS

The eye (Figure 9-2)The eye (Figure 9-2) Layers of eyeballLayers of eyeball

• Sclera—tough outer coat; “white” of eye; cornea is transparent Sclera—tough outer coat; “white” of eye; cornea is transparent part of sclera over irispart of sclera over iris

• Choroid—pigmented vascular layer prevents scattering of light; Choroid—pigmented vascular layer prevents scattering of light; front part of this layer made of ciliary muscle and iris, the colored front part of this layer made of ciliary muscle and iris, the colored part of the eye; the pupil is the hole in the center of the iris; part of the eye; the pupil is the hole in the center of the iris; contraction of iris muscle dilates or constricts pupilcontraction of iris muscle dilates or constricts pupil

• Retina (Figure 9-4)—innermost layer of the eye; contains rods Retina (Figure 9-4)—innermost layer of the eye; contains rods (receptors for night vision) and cones (receptors for day vision and (receptors for night vision) and cones (receptors for day vision and color vision)color vision)

Conjunctiva—mucous membrane covering the front surface of Conjunctiva—mucous membrane covering the front surface of the sclera and also lines the eyelid; kept moist by tears found the sclera and also lines the eyelid; kept moist by tears found in the lacrimal glandin the lacrimal gland

Lens—transparent body behind the pupil; focuses light rays on Lens—transparent body behind the pupil; focuses light rays on the retinathe retina



The eye (cont.)The eye (cont.) Eye fluidsEye fluids

• Aqueous humor—in the anterior chamber in front of the Aqueous humor—in the anterior chamber in front of the lenslens

• Vitreous humor—in the posterior chamber behind the lensVitreous humor—in the posterior chamber behind the lens Visual pathwayVisual pathway

• Innermost layer of retina contains rods and conesInnermost layer of retina contains rods and cones• Impulse travels from the rods and cones through the Impulse travels from the rods and cones through the

bipolar and ganglionic layers of retina (Figure 9-4)bipolar and ganglionic layers of retina (Figure 9-4)• Nerve impulse leaves the eye through the optic nerve; the Nerve impulse leaves the eye through the optic nerve; the

point of exit is free of receptors and is therefore called a point of exit is free of receptors and is therefore called a blind spotblind spot

• Visual interpretation occurs in the visual cortex of the Visual interpretation occurs in the visual cortex of the cerebrumcerebrum



The earThe ear The ear functions in hearing and in equilibrium The ear functions in hearing and in equilibrium

and balance—receptors called and balance—receptors called mechanoreceptorsmechanoreceptors

Divisions of the ear (Figure 9-5)Divisions of the ear (Figure 9-5)• External earExternal ear

Auricle (pinna)Auricle (pinna) External auditory canalExternal auditory canal

– Curving canal 2.5 cm (1 inch) in lengthCurving canal 2.5 cm (1 inch) in length– Contains ceruminous glandsContains ceruminous glands– Ends at the tympanic membraneEnds at the tympanic membrane



The earThe ear Divisions of the ear (cont.)Divisions of the ear (cont.)

• Middle earMiddle ear Houses ear ossicles—malleus, incus, and stapesHouses ear ossicles—malleus, incus, and stapes Ends in the oval windowEnds in the oval window The auditory (eustachian) tube connects the middle ear to the The auditory (eustachian) tube connects the middle ear to the

throatthroat Inflammation called Inflammation called otitis mediaotitis media

• Inner ear (Figure 9-6)Inner ear (Figure 9-6) Bony labyrinth filled with perilymphBony labyrinth filled with perilymph Subdivided into the vestibule, semicircular canals, and cochleaSubdivided into the vestibule, semicircular canals, and cochlea Membranous labyrinth filled with endolymphMembranous labyrinth filled with endolymph The receptors for balance in the semicircular canals are called The receptors for balance in the semicircular canals are called

cristae ampullariscristae ampullaris Specialized hair cells on the organ of Corti respond when bent by Specialized hair cells on the organ of Corti respond when bent by

the movement of surrounding endolymph set in motion by sound the movement of surrounding endolymph set in motion by sound waves (Figure 9-7)waves (Figure 9-7)



The taste receptors (Figure 9-8)The taste receptors (Figure 9-8) Receptors are chemoreceptors called Receptors are chemoreceptors called taste budstaste buds Cranial nerves VII and IX carry gustatory impulsesCranial nerves VII and IX carry gustatory impulses Most pathologists list four kinds of “primary” taste Most pathologists list four kinds of “primary” taste

sensations—sweet, sour, bitter, and saltysensations—sweet, sour, bitter, and salty• Metallic and umami (meaty) tastes are also unique and Metallic and umami (meaty) tastes are also unique and

may soon be added to the list of “primary” taste sensationsmay soon be added to the list of “primary” taste sensations

• Nasal congestion interferes with stimulation of olfactory Nasal congestion interferes with stimulation of olfactory receptors and thereby dulls taste sensationsreceptors and thereby dulls taste sensations

Gustatory and olfactory senses work together to permit Gustatory and olfactory senses work together to permit creation of many other taste sensationscreation of many other taste sensations



The smell receptors (Figure 9-9)The smell receptors (Figure 9-9) Receptors for fibers of olfactory or cranial Receptors for fibers of olfactory or cranial

nerve I lie in olfactory mucosa of nasal cavitynerve I lie in olfactory mucosa of nasal cavity Olfactory receptors are extremely sensitive but Olfactory receptors are extremely sensitive but

easily adapt (become fatigued)easily adapt (become fatigued) Odor-causing chemicals initiate a nervous Odor-causing chemicals initiate a nervous

signal that is interpreted as a specific odor by signal that is interpreted as a specific odor by the brainthe brain

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