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CHAPTER
31
Special Senses
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-2
Learning Outcomes
31.1 Describe the anatomy of the nose and the
function of each part.
31.2 Describe how smell sensations are created
and interpreted.
31.3 Describe the anatomy of the tongue and the
function of each part.
31.4 Describe how taste sensations are created
and interpreted.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-3
Learning Outcomes (cont.)
31.5 Name the four primary taste sensations and
the acknowledged fifth taste sensation.
31.6 Describe the anatomy of the eye and the
function of each part, including the accessory
structures and their functions.
31.7 Trace the visual pathway through the eye
and to the brain for interpretation.
31.8 Identify ways that patients can practice
preventive eye care.
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31-4
Learning Outcomes (cont.)
31.9 State ways that vision changes with age.
31.10 List the medical professionals involved in
diagnosis and treatment of visual disorders,
including the roles that each play in patient
care.
31.11 List treatments for visual disorders.
31.12 Describe the causes, signs and symptoms,
and treatments of various diseases and
conditions of the eye.
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31-5
Learning Outcomes (cont.)
31.13 Describe the anatomy of the ear and the
function of each part.
31.14 Explain the role of the ear in maintaining
equilibrium.
31.15 Explain how sounds travel through the ear
and are interpreted in the brain.
31.16 State ways that hearing changes with age.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-6
Learning Outcomes (cont.)
31.17 List the types of hearing loss and how they
differ.
31.18 Describe treatments for ear and hearing
disorders.
31.19 Explain how patients can be educated about
preventive ear care.
31.20 Describe the causes, signs and symptoms,
and treatments of various disorders of the
ear and hearing.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-7
Introduction
• Special senses
– Sensory receptors located in head
•
•
•
•
Nose – smell
Tongue – taste
Eyes – vision
Ears – hearing and equilibrium
–
Touch is a generalized sense
• Stimulus  nervous system  brain  response
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31-8
Nose and Sense of Smell
• Olfactory receptors
– Chemoreceptors –
respond to changes in
chemical
concentrations
– Chemicals must be
dissolved in mucus
– Located in the
olfactory organ
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31-9
Smell Sensation
Activation of smell receptors 
information sent to olfactory nerves
that send the information along
olfactory bulbs and tracts
to different areas of the cerebrum;
cerebrum interprets the information as a
particular type of smell
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31-10
Nose and Sense of Smell (cont.)
• Sensory Adaptation
– Chemical can stimulate receptors for
limited time
– Receptors fatigue and stop responding
to chemical
– No longer smell odor
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31-11
Apply Your Knowledge
You notice an odor coming from a patient when
you enter the exam room. Why would the patient
not be able to smell it?
ANSWER: After a few minutes, smell receptors undergo
sensory adaptation and no longer respond to the chemical,
and the patient can no longer smell the odor.
Very
Good!
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31-12
Tongue and Sense of Taste
• Gustatory receptors – located on
taste buds
• Taste buds
– Location
• Papillae of the tongue
• Roof of mouth
} fewer than on tongue
• Walls of throat
Tongu
e
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31-13
Tongue and Sense of Taste (cont.)
• Taste cells and supporting
structures
– On taste buds
– Supporting structures fill in space
– Taste cells
• Chemoreceptors
• Chemicals in food and drink must be
dissolved in saliva to activate
Tongu
e
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31-14
Tongue and Sense of Taste (cont.)
• Taste sensation
– 4 primary
• Sweet – tip
• Sour – sides
• Salty – tip and
sides
• Bitter – back
• Umami
– 5th basic taste
– Glutamic acid
• Spicy foods
– Activate pain
receptors
– Interpreted by brain
as “spicy”
Tongu
e
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31-15
Back
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31-16
Tongue and Sense of Taste (cont.)
Taste sensation
Activation of
taste cells
Cranial
nerves
Gustatory cortex of cerebrum
interprets information
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31-17
Apply Your Knowledge
What are the four primary taste sensations and
where are their corresponding taste cells
located?
ANSWER: The four primary taste sensations are:
Sweet – concentrated on the tip of the tongue
Sour – concentrated on the sides of the tongue
Salty – concentrated on the tip and sides of the tongue
Bitter – concentrated on the back of the tongue
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-18
Eye and Sense of Sight
• Vision system
– Eyes
– Optic nerves
– Vision centers in
the brain
– Accessory
structures
• Eye
– Processes light
to produce
images
– Three layers
– Two chambers
– Specialized parts
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31-19
Eye and Sense of Sight (cont.)
• Outer – sclera
– White of the eye
– Protects the eye
– Sense receptors
– Cornea
• Front of eye
• “Window” that allows
light into eye
• Bends light as it enters
Eye
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31-20
Eye and Sense of Sight (cont.)
• Middle – choroid
– Contains blood
vessels
– Iris
• Colored part of eye
• Muscle that
contracts and
relaxes to open or
close pupil
• Regulates the
amount of light that
enters the eye
– Ciliary body
• Muscles
• Controls the shape
of the lens
– Lens
• Posterior to iris
• Focuses light on
retina
– Accommodation
Eye
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31-21
Eye and Sense of Sight (cont.)
• Inner – retina
– Visual receptors
• Rods
– Sensitive to light
– Will function in dim
light – “limited”
night vision
– Do not provide
sharp image or
detect color
• Cones
– Function in bright
light
– Sensitive to color
and provide sharp
images
– Optic disc – optic
nerve enters retina
Eye
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31-22
Eye and Sense of Sight (cont.)
• Chambers of the eye
– Anterior chamber
• Front of lens
• Filled with aqueous humor – nourishes and
bathes anterior eye
– Posterior chamber
• Behind lens
• Contains vitreous humor – maintains shape of
eyeball and holds retina in place
Eye
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31-23
Back
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31-24
Visual Accessory Organs
• Eye orbits
– Eye sockets
– Form a protective
shell around the
eyes
– Eyebrows protect
eyes
• Eyelids
– Skin, muscle, and
connective tissue
– Blinking
• Prevents surface
from drying out
• Keeps foreign
material out of eye
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31-25
Visual Accessory Organs (cont.)
• Lacrimal
apparatus
– Mucous membranes
• Conjunctivas
– Line inner surfaces
of eyelids
– Lacrimal glands
• Lateral edge of
eyeballs
• Produce tears
– Nasolacrimal
ducts
• Medial aspect of
eyeballs
• Drain tears into
nose
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31-26
Visual Accessory Organs (cont.)
• Extrinsic eye muscles
–Six per eye move the eyeball
• Superiorly
• Inferiorly
• Laterally
• Medially
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31-27
Visual Pathways
• Eye works like a camera
– Light enters the eye through the lens
– Refraction – cornea, lens, and fluids bend
light to focus it on the retina
Image upside
down on retina
Retina converts
light to nerve
impulse
Image turned
right-side up
Optic
nerve
Optic
chiasm
Occipital
lobe of
cerebrum
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31-28
Eye Safety and Protection
• 90% of eye injuries are preventable
– Eye safety practices
• Adequate lighting/handrails
• Pad or cushion sharp edges on furniture
• Toys should be age-appropriate
• Do not mix chemicals
– Proper protective wear
• Goggles
• Sports eye guards
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31-29
Apply Your Knowledge
Matching: ANSWER:
___
G Middle layer of eye
H Eye sockets
___
___
F Control shape of lens
___
D Outer layer of eye
___
B Anterior chamber
A Tears
___
___
I Bending of light
___
E Posterior chamber
C Inner layer of eye
___
A. Lacrimal glands
B. Aqueous humor
C. Retina
D. Sclera
E. Vitreous humor
F. Ciliary body
G. Choroid
H. Orbits
I. Refraction
Out of
Sight!
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31-30
The Aging Eye
• Eyelids may droop
• Quality and quantity
of tears decrease
• Conjunctiva thins and
eyes may become
dryer
• Cornea yellows, fat
deposits around it
• Brown spots on sclera
• Pupils become
smaller
• Lens denser and more
rigid
• Lens yellows
• Retinal changes – vision
fuzzy
• Changes in ability of eye
to adapt to light
• Impaired night vision
• Decreased peripheral
vision; depth perception
• Floaters or flashes of light
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31-31
Preventing Falls in the Elderly
• Falls can result in fractures of major bones
• Complications of falls can lead to death
• Prone to falling
– Vision problems
– Poor health
– Slower reflexes
– Equilibrium problems
– Medication
• Patient education
– Safety checklist
– Precautions
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31-32
Apply Your Knowledge
What vision changes can occur in the elderly
patient?
ANSWER: An elderly patient may have difficulty seeing
because of drooping eyelids. Focusing may be more
difficult because less light enters the eye. He may have
difficulty distinguishing colors due to yellowing of the
lens. Vision may be fuzzy because of changes in the
retina. Night vision can become impaired. The patient
may see floaters or “sparks.”
Nice job!
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31-33
Vision Testing
• Professionals include
– Ophthalmologist – medical doctor who
is an eye specialist
– Optometrist – provides vision
screening and diagnostic testing
– Opticians – fills vision prescriptions for
glasses and contacts
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31-34
Vision Screening Tests
• Myopia – impairment
of distance vision
– Eyeball is too long
– Light focuses anterior
to retina
– Snellen chart
– Normal vision
• 20/20
• Hyperopia –
impairment of near
vision
– Eyeball is shorter
– Light focused posterior
to retina
– Test using a handheld
chart with various
sizes of print
– Presbyopia
• Impairment due to
aging
• Loss of lens elasticity
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31-35
Vision Screening Tests (cont.)
• Contrast sensitivity
– Distinguish shades of
gray
– Testing
• Pelli-Robson contrast
sensitivity chart
• Vistech Consultants
vision contrast system
– Detect cataracts or
retinal problems
before sharpness is
impaired
• Color vision
– Color-blindness
• May be inherited
• More common in
males
– Tests
• Ishihara color system
• Richmond
pseudoisochromatic
color test
– Difficulties may
indicate retinal or optic
nerve disease
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31-36
Apply Your Knowledge
What is the difference between myopia and
hyperopia and what is presbyopia? What effect
does each have on vision?
ANSWER: If the patient has myopia, the eyeball is elongated and
light focuses in front of the retina. She will have difficulty seeing
far away. If she has hyperopia, the eyeball is shorter than normal
and light focuses behind the retina. With presbyopia, the lens loses
elasticity due to aging, resulting in the inability to see things close
up.
Reyeght!
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31-37
Treating Eye Problems
• Delicate organ – caution and sterile
technique necessary
• Patient education on preventive care
• Eye irrigation
• Administration
– Sterile solution
of medications
– Only ophthalmic
medications
– Avoid touching
dropper or ointment
tube to the eye
– Purpose
• Remove foreign
material
• Relieve discomfort
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31-38
Common Diseases and Disorders
Disorder/Disease
Description
Amblyopia
Lazy eye; one eye is not used regularly; poor
depth perception; often concurrent with
strabismus
Astigmatism
Cornea or lens has abnormal shape; blurred
images
Cataracts
Opaque structures in lens prevent light from
passing through; vision fuzzy
Conjunctivitis
Pink eye; highly contagious bacterial infection
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31-39
Common Diseases and Disorders (cont.)
Disorder/Disease
Description
Dry eye syndrome
Common problem; decreased production of oil
in tears
Entropion
Inversion of lower eyelid
Glaucoma
Increase in intraocular pressure due to a buildup
of aqueous humor in anterior chamber
Hyperopia
Farsightedness
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31-40
Common Diseases and Disorders (cont.)
Disorder/Disease
Description
Macular
degeneration
Progressive disease; inadequate blood supply to
retina; most common cause of vision loss;
affects people over 50 years
Myopia
Nearsightedness
Nystagmus
Rapid, involuntary eye movements
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31-41
Common Diseases and Disorders (cont.)
Disorder/Disease
Description
Presbyopia
Loss of lens elasticity; develops with age
Retinal detachment Layers of retina separate; medical emergency
Strabismus
Convergent
Misalignment of eyes
Crossed eyes; one or both eyes turn inward
Wall eye; one or both eyes turn outward
Divergent
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31-42
Apply Your Knowledge
It is okay to use any solution or medication in the
eye?
ANSWER: Only medications or solutions specifically
designated for ophthalmic use may be used in the eyes.
Medications not designated for the eye may be too
concentrated or contain substances that can injure the
eye. Solutions should be sterile and care must be taken
not to contaminate the tip of the dropper or bottle.
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31-43
The Ear
• External ear
– Auricle (pinna)
• Collects sound waves
– External auditory canal
• Guides sound wave to tympanic membrane
– Tympanic membrane
• Separates external canal and middle ear
• Vibrates when sound hits it
Ear
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31-44
The Ear (cont.)
• Middle ear
– Ear ossicles
• Malleus
• Incus
• Stapes
– Ossicles vibrate in
response to
vibration of
tympanic
membrane
– Eustachian tube
• Connects middle ear
to throat
• Equalizes pressure
on eardrum
– Oval window
• Separates middle ear
from inner ear
Ear
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31-45
The Ear (cont.)
• Inner ear – labyrinth of
communicating chambers
– Semicircular canals – detect balance
of the body
– Vestibule – equilibrium
– Cochlea
• Hearing receptors
– Organ of Corti – organ of hearing
Ear
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31-47
Equilibrium
• Head movement causes fluid in
semicircular canals and
vestibule to move
• Equilibrium receptors transmit
information along vestibular
nerves to cerebrum
• Cerebrum determines if body needs to
make adjustments
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31-48
Sense of Hearing
• Sound waves collected
• Waves cause tympanic membrane
to vibrate
• Ossicles amplify vibrations, which
enter inner ear
• Movement of hairs lining cochlea trigger
nerve impulses
• Impulses are transmitted by auditory nerve
to the brain for interpretation
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31-49
Sense of Hearing (cont.)
• Bone conduction
– Alternative pathway
– Bypasses external
and middle ear
directly to inner
– Useful in
determining cause
of hearing problem
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-50
Apply Your Knowledge
Matching:
ANSWER:
___
E Pinna
A. Organ of Corti
___
C Malleus, incus, and stapes B. Cerumen
___
F Hearing receptors
C. Ear ossicles
___
G Inner ear
D. Tympanic membrane
___
A Organ of hearing
E. Auricle
___
B Earwax
F. Cochlea
___
D Eardrum
G. Labyrinth
___
H Detect balance of body
H. Semicircular canals
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31-51
How to Recognize Hearing Problems in
Children
• Guidelines
– Infants to 4 months
• Startled by loud noises
• Recognize mother’s voice
– 4 to 8 months
• Regularly follow sounds
• Babble at people
– 8 to 12 months
• Respond to the sound of their
name
• Respond to “no”
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31-52
The Aging Ear
•
•
•
•
External ear larger / earlobe longer
Cerumen dryer and prone to impaction
Ear canal narrower
Eardrum shrinks and appears dull and
gray
• Ossicles do not move as freely
• Semicircular canals less sensitive to
changes in position – affects balance
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-53
Apply Your Knowledge
What problem with the aging ear makes the
elderly more prone to falls?
ANSWER: The semicircular canals become less sensitive
to change in position, which affects balance. This
problem with equilibrium results in increased chance of
falls in the elderly.
Great
Answer!
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-54
Hearing Loss
• Symptom of a disease, not a normal part of
aging
• Conductive hearing loss
– Interruption in
transmission to inner ear
– Causes
• Obstruction of ear canal
• Infection of middle ear
• Reduced movement of
stirrup
• Sensorineural hearing
loss
– Sound waves not perceived
by brain as sound
– Causes
• Hereditary
• Repeated exposure to
loud noises/viral infections
• Side effect of medication
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31-55
Hearing Loss (cont.)
• Noise pollution – causes damage to sensitive
cells in cochlea
• Working with the hearing-impaired patient
– Speak at a reasonable volume, in clear, low-pitched
volumes
– Face the person; use hand gestures, if appropriate
– Do not overemphasize lip movements
– Have patient repeat message to verify understanding
– Treat hearing-impaired patients with patience and
respect
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31-56
Hearing and Diagnostic Tests
• Hearing tests
– Tuning forks – differentiate between types of
loss
– Audiometer – measures hearing acuity
• Diagnostic testing
– Tympanometry
• Measures the ability of the eardrums to move
• Detects diseases and abnormalities of the middle
ear
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-57
Apply Your Knowledge
Identify the types of hearing loss based on the description
below. What can be used to differentiate between the
two?
Answer:
A tuning fork is a simple test to distinguish between
types of hearing loss.
Conductive hearing loss


Interruption in transmission to
inner ear
Causes

Obstruction of ear canal

Infection of middle ear

Reduced movement of
stirrup
Sensorineural hearing loss


Sound waves not perceived by
brain as sound
Causes

Hereditary

Repeated exposure to loud
noises/viral infections

Side effect of medication
Bravo!
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-58
Treating Ear and Hearing Problems
• Patient education
– Preventative ear care
– Administer ear medications
• Medications and irrigation
– Relieve inflammation or irritation of canal
– Loosen and remove impacted cerumen or
foreign body
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31-59
Treating Ear and Hearing Problems (cont.)
• Hearing aids
– Obtaining a hearing aid
• Otologist – medical
doctor specializing in
health of ear
• Audiologist – evaluates
and corrects hearing
problems
• Other devices / strategies
– Amplifiers
– Closed-captioning
– Appliances that light up as
well as ring
– Care and use
• Batteries
• Routine cleaning
• Keep dry and avoid hair
sprays
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-60
Common Diseases and Disorders
Disorder/Disease
Description
Cerumen impaction
Build up of wax within external auditory canal
Hearing loss
Deafness
Ménière's disease
Disturbance in equilibrium characterized by
vertigo and tinnitus
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-61
Common Diseases and Disorders
Disorder/Disease
Description
Otitis
Otitis externa
Otitis media
Otitis interna
Inflammation of the ear
Swimmers’ ear
Middle ear infection; common infection
Labyrinthitis; inner ear infection
Osteosclerosis
Immobilization of the stapes; common cause
of conductive hearing loss
Presbycusis
Hearing loss due to aging process
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-62
Apply Your Knowledge
True or False:
ANSWER:
___
F An audiologist is a physician that specializes in ear health.
___
F Otitis media is also called swimmers’ ear.
otologist
externa
___
T Presbycusis is hearing loss due to the aging process.
___
F Vertigo is ringing in the ears.
Tinnitus
___
T Otitis interna is an inflammation of the labyrinth.
___
T Ménière's disease is characterized by disturbances in equilibrium.
___
T Otosclerosis is the immobilization of the stapes.
___
F Tinnitus is dizziness.
Vertigo
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31-63
In Summary
31.1 Olfactory receptors, which are the sense receptors for
the sense of smell, are found in the olfactory organ
located in the upper part of the nasal cavity.
31.2 When the olfactory receptors are activated, they send
information to the olfactory nerves, then on to the
cerebellum for interpretation.
31.3 Gustatory receptors are found on the taste buds,
which are located on the papillae (bumps) of the
tongue.
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31-64
In Summary (cont.)
31.4 Gustatory receptors are chemoreceptors which are
activated by the chemicals found in food and drink as
they are dissolved in the mouth’s saliva. The
information is brought to the gustatory cortex of the
parietal lobe of the brain for interpretation.
31.5 The four primary taste sensations are, sweet, salty,
sour and bitter. Each has a “specialized” area of the
tongue where each taste is most pronounced. The
fifth recognized taste sensation is umami.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-65
In Summary (cont.)
31.6 The eye is composed of three layers. The sclera is
the outer protective layer and includes the cornea.
The middle vascular layer is the choroid, consisting of
the iris, pupil, ciliary body, and lens, and is the area of
light regulation and focusing. The innermost layer is
the retina containing the rods and cones, the optic
nerve, and optic disk. This is where the nerve impulse
is picked up and brought to the brain for
interpretation. The accessory organs are the orbits,
eyelids, conjunctivas, lacrimal apparatus, and
extrinsic eye muscles, all of which are protective for
the eye.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-66
In Summary (cont.)
31.7 The cornea, lens, and fluids focus light on the retina.
The retina converts the image into nerve impulses,
which are transmitted by the optic nerve to the brain
for interpretation.
31.8 Eye safety and injury prevention includes, but is not
limited to, adequate lighting and availability of hand
rails, keeping personal and sharp items out of reach
of children, wearing of safety goggles when operating
power equipment and using chemicals, and not
mixing cleaning agents.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-67
In Summary (cont.)
31.9 Changes in the aging eye include, but are not limited
to, diminishing fat tissue, decreased tear production,
thinner and dryer conjunctiva, brown spots in the
sclera, changes in the iris resulting in smaller pupil,
lens becoming denser and more rigid, as well as lens
and retinal changes causing fuzziness of vision and
difficulty distinguishing colors.
31.10 Ophthalmologists (M.D.), optometrists (O.D.), and
opticians are all professionals who deal with eye and
vision health.
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31-68
In Summary (cont.)
31.11 All treatments for eye problems include use of sterile
technique and extreme caution to protect the
delicate tissues of the eye. Eye irrigations and
medication installations are common treatments.
Instruction on these techniques will take place in the
Drug Administration chapter.
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31-69
In Summary (cont.)
31.12 Common diseases and disorders of the eye include
amblyopia, astigmatism, cataracts, conjunctivitis,
hyperopia, myopia and presbyopia. More detailed
information on the signs, symptoms, and treatments
for these conditions, as well as other common eye
disorders, is found in the Pathophysiology section of
this chapter, directly after the A&P section on the
eye.
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31-70
In Summary (cont.)
31.13 There are three parts to the ear. The external ear
includes the auricle or pinna and external auditory
canal to the tympanic membrane. The middle ear
begins at the tympanic membrane and ends at the
oval window and includes the ear ossicles. The inner
ear is composed of the labyrinth and contains the
organ of Corti as well as perilymph and endolymph,
the fluids of hearing.
31.14 The semicircular canals and vestibule in the inner
ear function in the equilibrium and balance of the
body, sending impulses to the vestibular nerves,
which transmit information to the cerebrum for
interpretation.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-71
In Summary (cont.)
31.15 The outer ear collects sound waves and channels
them to the tympanic membrane, which vibrates.
The vibrations are amplified by the ear ossicles and
enter the inner ear and cochlea. The movements of
the hairs in the cochlea trigger nerve impulses that
are transmitted by the auditory nerve to the brain.
31.16 Aging causes the eardrum to shrink. The joints
between the ossicles degenerate so there is less
freedom of movement, which causes decrease in
hearing acuity.
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In Summary (cont.)
31.17 Conductive hearing loss is the result of sound wave
transmission interruption, as with cerumen impaction
and tumors or infections. Sensorineural hearing loss
is the result of nerve damage so that the brain
cannot perceive sounds waves as sound.
31.18 Ear treatments depend on the condition being
treated, but may include ear irrigation and
medication installation as well as hearing aids and/or
surgery for hearing loss.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-73
In Summary (cont.)
31.19 Preventative ear care includes, but is not limited to,
routine hearing exams; avoiding the insertion of
small items into the ear canal; and using care when
using cotton swabs. Ear protection should be used
when exposed to loud or prolonged noise. Use
medications such as ear drops properly and watch
for signs of ear or hearing problems.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
31-74
In Summary (cont.)
31.20 The pathophysiology section on ear and hearing
diseases and conditions is found at the end of the
A&P section for the ear. Signs, symptoms, and
treatments of cerumen impaction, hearing loss,
Ménière's disease, otitis, otosclerosis, and other
common problems are outlined in this section.
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.
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End of Chapter 31
Every closed eye is
not sleeping, and
every open eye is
not seeing.
~ Bill Cosby
© 2011 The McGraw-Hill Companies, Inc. All rights reserved.