Download Chapter 9 The Senses

Chapter 9
The Senses
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 1
CLASSIFICATION OF SENSE
ORGANS

General sense organs (Table 9-1)

Often exist as individual cells or receptor units
 Widely distributed throughout the body

Special sense organs (Table 9-2)

Large and complex organs
 Localized grouping of specialized receptors
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Slide 2
CLASSIFICATION OF SENSE
ORGANS (cont.)

Classification by presence or absence of covering
capsule

Encapsulated
 Unencapsulated (“free” or “naked”)

Classification by type of stimuli required to activate
receptors
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Photoreceptors (light)
Chemoreceptors (chemicals)
Pain receptors (injury)
Thermoreceptors (temperature change)
Mechanoreceptors (movement or deforming of capsule)
Proprioceptors (position of body parts or changes
in muscle length or tension)
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Slide 3
CONVERTING A STIMULUS
INTO A SENSATION

All sense organs have common functional
characteristics

All are able to detect a particular stimulus
 A stimulus is converted into a nerve impulse
 A nerve impulse is perceived as a sensation
in the central nervous system
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Slide 4
GENERAL SENSE ORGANS
(Table 9-1)


Distribution is widespread; single-cell receptors
are common
Examples (Figure 9-1, Table 9-1)
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Free nerve endings—pain, temperature, and crude
touch
Tactile (Meissner) corpuscles—fine touch and
vibration
Bulbus (Ruffini) corpuscles—touch and pressure
Lamellar (Pacinian) corpuscles—pressure and
vibration
Bulboid corpuscles (Krause end-bulbs)—touch
Golgi tendon receptors—proprioception
Muscle spindles—proprioception
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Slide 7
SPECIAL SENSE ORGANS

The eye (Figure 9-2)

Layers of eyeball
• Sclera—tough outer coat; “white” of eye; cornea is transparent
part of sclera over iris
• Choroid—pigmented vascular layer prevents scattering of light;
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; contraction of iris muscle dilates or constricts pupil
• Retina (Figure 9-4)—innermost layer of the eye; contains rods
(receptors for night vision) and cones (receptors for day vision
and color vision)

Conjunctiva—mucous membrane covering the front surface
of the sclera and also lines the eyelid; kept moist by tears
found in the lacrimal gland
 Lens—transparent body behind the pupil; focuses light rays
on the retina
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Slide 8
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Slide 11
SPECIAL SENSE ORGANS (cont.)

The eye (cont.)

Eye fluids
• Aqueous humor—in the anterior chamber in front of
the lens
• Vitreous humor—in the posterior chamber behind the
lens

Visual pathway
• Innermost layer of retina contains rods and cones
• Impulse travels from the rods and cones through the
bipolar and ganglionic layers of retina (Figure 9-4)
• Nerve impulse leaves the eye through the optic
nerve; the point of exit is free of receptors and is
therefore called a blind spot
• Visual interpretation occurs in the visual cortex of the
cerebrum
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Slide 12
SPECIAL SENSE ORGANS (cont.)

The ear

The ear functions in hearing and in equilibrium and
balance—receptors called mechanoreceptors
 Divisions of the ear (Figure 9-5)
• External ear


Auricle (pinna)
External auditory canal
– Curving canal 2.5 cm (1 inch) in length
– Contains ceruminous glands
– Ends at the tympanic membrane
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Slide 13
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Slide 14
SPECIAL SENSE ORGANS (cont.)

The ear (cont.)

Divisions of the ear (cont.)
• Middle ear
Houses ear ossicles—malleus, incus, and stapes
 Ends in the oval window
 The auditory (eustachian) tube connects the middle ear to the
throat
 Inflammation called otitis media
• Inner ear (Figure 9-6)
 Bony labyrinth filled with perilymph
 Subdivided into the vestibule, semicircular canals, and cochlea
 Membranous labyrinth filled with endolymph
 The receptors for balance in the semicircular canals are called
cristae ampullaris
 Specialized hair cells on the organ of Corti respond when bent
by the movement of surrounding endolymph set in motion
by sound waves (Figure 9-7)

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SPECIAL SENSE ORGANS (cont.)

The taste receptors (Figure 9-8)

Receptors are chemoreceptors called taste buds
 Cranial nerves VII and IX carry gustatory impulses
 Most pathologists list four kinds of “primary” taste
sensations—sweet, sour, bitter, and salty
• Metallic and umami (meaty) tastes are also unique and
may soon be added to the list of “primary” taste
sensations
• Nasal congestion interferes with stimulation
of olfactory receptors and thereby dulls taste
sensations

Gustatory and olfactory senses work together
to permit creation of many other taste sensations
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Slide 19
SPECIAL SENSE ORGANS (cont.)

The smell receptors (Figure 9-9)

Receptors for fibers of olfactory or cranial nerves lie
in olfactory mucosa of nasal cavity
 Olfactory receptors are extremely sensitive but
easily adapt (become fatigued)
 Odor-causing chemicals initiate a nervous signal
that is interpreted as a specific odor by the brain
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