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Chapter 9 The Senses

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Chapter 9 The Senses
Chapter 9
The Senses
Jeanelle F. Jimenez RN, BSN, CCRN
CLASSIFICATION OF SENSE ORGANS

General sense organs (Table 9-1)
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
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Often exist as individual cells or receptor units
Widely distributed throughout the body
Special sense organs (Table 9-2)
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
Large and complex organs
Localized grouping of specialized receptors
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CLASSIFICATION OF SENSE ORGANS

Classification by presence or absence of covering
capsule
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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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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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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
Meissner’s corpuscles—fine touch and
vibration
Ruffini’s corpuscles—touch and pressure
Pacinian corpuscles—pressure and vibration
Krause’s end-bulbs—touch
Golgi tendon receptors—proprioception
Muscle spindles—proprioception
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SPECIAL SENSE ORGANS

The eye (Figure 9-2)
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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)
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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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SPECIAL SENSE ORGANS

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 10
SPECIAL SENSE ORGANS

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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SPECIAL SENSE ORGANS

The ear
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Divisions of the ear (cont.)
• Middle ear

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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)

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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

The taste receptors (Figure 9-8)
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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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SPECIAL SENSE ORGANS

The smell receptors (Figure 9-9)
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

Receptors for fibers of olfactory or cranial
nerve I 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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