Transcript Chapter_020

CHAPTER 20
SENSORY SYSTEM
Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.
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Chapter 20 Learning Objectives

Define at least 10 terms relating to the
sensory system.

Describe the function of the sensory system.

Identify at least 10 sensory system structures
and the function of each.
Copyright © 2012, 2007, 2003, 1997, 1991 by Mosby, Inc., an affiliate of Elsevier Inc.
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Chapter 20 Learning Objectives

Identify at least three methods of assessment
of the sensory system.

Describe at least five disorders of the sensory
system.
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Structure and Function

The sensory system consists of receptors in
specialized cells and organs that perceive
changes in the internal and external
environment.

Stimuli generate nerve impulses that are sent
to the brain for interpretation.
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Structure and Function

Environmental stimuli are perceived by
means of

Vision
 Hearing
 Touch
 Taste
 Position
 Balance
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Eye

The eye is most important sensory organ,
because 90% of the information about the
environment reaches the brain from the eyes.

Movement of the eye is controlled by the
extrinsic muscles.

Only one fifth of the eye is exposed to the
environment.
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Eye

The eyeball is not solid.

Divided into cavities (anterior and posterior)
• Anterior filled with aqueous humor
• Posterior filled with vitreous humor
• Aqueous and vitreous humors help maintain shape
of the eye


Iris is a round, colored muscle that adjusts the
amount of light entering the eye.
Lens is a convex, transparent tissue that focuses
and directs incoming light on the retina of the eye.
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Structure of the Eye
FIGURE 20-1 Structures of the eye. (From Sorrentino SA: Mosby’s
textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)
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Eye

Vision is similar to the action of a camera.

Refraction
•

Accommodation
•

Lens bends light rays as they enter the eye to
focus on the retina.
The lens changes shape to focus near and far.
Converge
•
Single binocular vision occurs, and only one
object is seen.
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Eye

Rods and cones are specialized cells in the
retina that absorb light.


Rods are sensitive to dim light.
Cones
•
•

React to bright light
Allow color distinction through three types of
pigments that recognize primary colors
Impulses released by pigments in rods and
cones are transmitted to the brain by the
optic nerve.
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The Eye Functions Like a Camera
FIGURE 20-2 The eye functions like a camera.
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Ear

Main functions of the ear



Auditory or acoustic sense (hearing) is the primary
function of the ear.
Hearing helps to maintain equilibrium.
Three main parts of the ear

External
 Middle
 Inner
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Parts of the Ear

External ear


The shape channels incoming sound waves
Specialized glands in the ear canal produce
cerumen, which protects the middle ear.
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Parts of the Ear

Middle ear
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Air-filled chamber
• Tympanic membrane changes sound waves into
mechanical movements.
• Auditory bones transmit sound vibrations.
• Ossicles amplify and transmit sound to the inner
ear.

Eustachian tube allows pressure of air in the
middle ear to be equalized with the air pressure of
the environment
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Parts of the Ear

Inner ear

Contains a series of canals called the bony
labyrinth.
• Movement of fluid and hair cells lining the cochlea
converts the mechanical vibration from the ossicles
to neural impulses.
• Semicircular canals contain endolymph that gives a
sense of balance when body is in motion.
• Vestibule has two chambers (saccule and utricle)
that maintain resting equilibrium.
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Structure of the Ear
FIGURE 20-3 Structures of the ear.
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Tongue


Taste, or the gustatory sense, is perceived by
specialized cells located in papillae on the
tongue called taste buds.
Five tastes are perceived by all areas of the
tongue.


Sweet, sour, bitter, salty, and umami (meatiness)
Flavor is identified by smell and taste.
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Taste Buds
FIGURE 20-4 Taste buds are located on the tongue. (From Patton KT,
Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)
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Nose



Olfactory sense originates in olfactory
receptor cells in the nose that immediately
transmit impulses to the brain through the
olfactory cranial nerves.
The nasal cavity is divided into two
sections by the septum.
Olfactory receptor neurons are stimulated
by chemicals (gases) in the air.
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Nose

Smells can




Reduce stress
Affect blood pressure
Recall memories
Aid the sense of taste
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Nose and Surrounding Structure
FIGURE 20-5 The nose and surrounding structures.
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Skin

The skin can sense touch, pressure, temperature,
and pain through five specialized cells:

Meissner's corpuscles
• Sense light touch and motion

Pacinian corpuscles
• Sense deep pressure

End-bulbs of Krause
• Sense cold, low-frequency vibrations, two-point
discrimination
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Skin

Corpuscles of Ruffini
• Sense heat, deep pressure, and continuous touch

Nociceptors
• Pain receptors
• Respond to more than one stimulus
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Nerve Receptors of the Skin
FIGURE 20-6 Nerve receptors of the skin. A, Meissner’s corpuscle
(touch). B, Pacinian corpuscle (pressure). C, Krause’s end-bulb. D,
Ruffini nerve endings (warmth). E, Free nerve endings (pain).
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Assessment Techniques
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Sight
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Ophthalmoscope to examine inner structure of the
eye
Visual acuity with the Snellen test
Tonometer to measure pressure of the inner eye
Color blindness chart to identify defects in color
determination
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Assessment Techniques
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Hearing
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Otoscope to view the structures of ear
Audiometer to measure hearing ability
Impedance testing to measure flexibility of the
tympanic membrane
Rinne’s test using a tuning fork to assess
transmission of sound through the ear structure
Weber's test using tuning fork to test for unilateral
or one-sided hearing loss
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Hearing Aid
FIGURE 20-9 Hearing Aid. (Courtesy Siemens Hearing Instruments, Inc., Piscataway, NJ.
In Sorrentino SA: Mosby’s textbook for nursing assistants, ed 7, St. Louis, 2008, Mosby.)
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Eye Examination
FIGURE 20-7 Eye examination. A, Ophthalmoscope.
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Ophthalmoscopic View of the
Retina
FIGURE 20-7 Eye examination. B, Retina.
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Disorders of the Sensory System
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Achromatism

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Amblyopia
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Also called color blindness, it is a common
inherited defect.
Also called lazy eye, it is poor vision in one eye
often resulting from better vision in the other eye
during infancy or early childhood.
Anacusis

Hearing loss resulting from damage to neural
tissues
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Disorders of the Sensory System
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Astigmatism

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Cataract
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Congenital defect causing imperfect curvature of
the cornea and resulting in blurred vision
Clouding of the lens that causes blurred or partial
vision
Conjunctivitis

Also called pink eye, it is a bacterial or viral
inflammation of the eyelid.
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Cataracts
FIGURE 20-10 Cataracts cause blurred or partial vision. (From Patton KT,
Thibodeau GA: Anatomy & physiology, ed 7, St. Louis, 2010, Mosby.)
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Disorders of the Sensory System

Deafness



Complete loss of hearing in one or both ears
Inherited or caused by complications at birth,
disease, excessive noise, or ototoxic drugs
Diabetic retinopathy

Condition of damaged blood vessels in the retina
caused by uncontrolled diabetes mellitus
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Cochlear Implant
FIGURE 20-11 Cochlear implant. (Courtesy of Stephanie Freese, artist, and American
Scientist, The Magazine of Sigma Xi, The Scientific Research Society. In Gould BE, Dyer
R: Pathophysiology for the health professions, ed 4, St. Louis, 2011, Saunders.)
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Disorders of the Sensory System

Diplopia

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Epistaxis


Also called double vision, it results from muscle
imbalance or paralysis of an extraocular muscle.
Nosebleed resulting from disease, trauma, or
other conditions such as hypertension, leukemia,
or rheumatic fever
Glaucoma

Increased pressure inside the eye caused by
trauma or hereditary factors
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Disorders of the Sensory System

Hyperopia


Farsightedness resulting from a congenital
deformity in the eye
Macular degeneration

Slow or sudden, painless loss of central vision
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Disorders of the Sensory System

Ménière's disease
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
Myopia

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Collection of fluid in the labyrinth of the ear leading
to dizziness, ringing in the ear (tinnitus), pressure,
and eventual deafness
Nearsightedness resulting from a congenital
deformity in the eye
Night blindness

Poor vision in dim light that results from a
deficiency in the rods of the retina
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Disorders of the Sensory System

Otitis media

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Presbyopia


Middle ear bacterial or viral infection common in
young children
Type of farsightedness related to aging
Retinal detachment

Result of injury or uncontrolled diabetes mellitus
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Otitis Media
FIGURE 20-12 Otitis media is a common among young children. (From Damjanov I:
Pathology for the health professions, ed 3, St. Louis, 2006, Saunders.)
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Disorders of the Sensory System
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Rhinitis
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Ruptured eardrum


Inflammation of the lining of the nose caused by
allergic reaction, viral infection, sinusitis, or
chemical irritants
Results from infection, an explosion, a blow to the
head, or a sharp object inserted into the ear
Sinusitis

Chronic or acute inflammation of a sinus (usually
paranasal)
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Disorders of the Sensory System

Strabismus


Condition in which both eyes do not focus on the
same point or direction
Stye

Bacterial infection of the sebaceous glands of the
eyelid
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Issues and Innovations

Visual correction by surgery


Radial keratotomy (microscopic surgery)
Epikeratophakia
•

Photorefractive keratectomy (PRK) (laser surgery)
•

Intacs (intracorneal rings)
Intacs (intracorneal rings)
Noise pollution


Inner ear damage is permanent.
Loud music and phones can cause hearing loss.
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Summary


The function of the sensory system is to
perceive changes in the internal and external
environment with specialized receptors.
Sensory system structures

Eye
 Ear
 Tongue
 Nose
 Skin
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Summary

Methods of assessment of the sensory
system



Snellen chart
Otoscope
Rinne test
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Summary

Disorders of the sensory system





Conjunctivitis
Epistaxis
Glaucoma
Macular degeneration
Rhinitis
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