The document outlines objectives and content for a lecture on the special senses. It will cover the anatomy and physiology of the eye, vision, chemical senses of taste and smell, ear structures for hearing and balance, and developmental aspects. Key topics include the accessory eye structures, layers of the eyeball, photoreception and visual pathways, olfactory and gustatory receptors, structures of the outer, middle and inner ear, mechanisms of hearing and equilibrium, and age-related changes to the special senses. Laboratory exercises and histology slides are listed to supplement the lecture material.

1. The Special Senses
Objectives
The Eye and Vision
1. List and explain the structure and function of the accessory eye structures.
2. Describe the structure and function of the three tunics of the eyeball.
3. Examine the internal chambers of the eye.
4. Discuss refraction and the focusing of light in the eyeball. Relate this to focusing for distance vision
and focusing for close vision.
5. Identify the photoreceptors. Be sure to include stimulation, anatomy, chemistry, and light transduction.
6. Explain the visual pathways to the brain.
7. Discuss visual processing.
8. List and discuss homeostatic disorders of the eye and vision.
The Chemical Senses: Taste and Smell
9. Describe the location, structure and afferent pathways for the taste and smell receptors.
10. Explain activation of taste and smell receptors.
The Ear: Hearing and Balance
11. Explore the structure of the outer, middle, and inner ear.
12. Describe the physiology of sound.
13. Explain the auditory pathway to the brain.
14. Define tinnitus and Ménière’s syndrome.
15. Discuss the sense of equilibrium; identify where the receptors are located and what they respond to.
16. Examine the equilibrium pathway to the brain.
Developmental Aspects of the Special Senses
17. List and discuss developmental accomplishments and aging concerns for hearing, vision, taste, and
smell.
Suggested Lecture Outline
I. The Eye and Vision (pp. 556–578; Figs. 15.1–15.20)
A. Vision is our dominant sense with 70% of our body’s sensory receptors found in the eye.
B. Accessory Structures of the Eye (pp. 556–559; Figs. 15.1–15.3)
1. Eyebrows are short, coarse hairs overlying the supraorbital margins of the eye that shade the
eyes and keep perspiration out.
2. Eyelids (palpebrae), eyelashes, and their associated glands help to protect the eye from
physical danger as well as from drying out.
3. Conjunctiva is a transparent mucous membrane that lines the eyelids and the whites of the
eyes. It produces a lubricating mucus that prevents the eye from drying out.

2. 4. The lacrimal apparatus consists of the lacrimal gland, which secretes a dilute saline solution
that cleanses and protects the eye as it moistens it, and ducts that drain excess fluid into the
nasolacrimal duct.
5. The movement of each eyeball is controlled by six extrinsic eye muscles that are innervated by
the abducens and trochlear nerves.
C. Structure of the Eyeball (pp. 559–565; Figs. 15.4–15.9)
1. Three layers form the wall of the eyeball.
a. The fibrous tunic is the outermost coat of the eye and is made of a dense avascular
connective tissue with two regions: the sclera and the cornea.
b. The vascular tunic (uvea) is the middle layer and has three regions: the choroid, the ciliary
body, and the iris.
c. The inner layer (retina) is the innermost layer made up of two layers: the outer pigmented
layer absorbs light; the inner neural layer contains millions of photoreceptors (rods and
cones) that transduce light energy.
2. Internal Chambers and Fluids
a. Posterior segment (cavity) is filled with a clear gel called vitreous humor that transmits light,
supports the posterior surface of the lens, holds the retina firmly against the pigmented
layer, and contributes to intraocular pressure.
b. Anterior segment (cavity) is filled with aqueous humor that supplies nutrients and oxygen
to the lens and cornea while carrying away wastes.
3. The lens is an avascular, biconcave, transparent, flexible structure that can change shape to
allow precise focusing of light on the retina.
D. Physiology of Vision (pp. 565–578; Figs. 15.10–15.20)
1. Overview: Light and Optics
a. Electromagnetic radiation includes all energy waves from long waves to short waves, and
includes the visible light that our eyes see as color.
b. Refraction of a light ray occurs when it meets the surface of a different medium at an
oblique angle rather than a right angle.
2. Focusing of Light on the Retina
a. Light is bent three times: as it enters the cornea and on entering and leaving the lens.
b. The far point of vision is that distance beyond which no change in lens shape is required
(about 6 m or 20 ft.).
c. Focusing for close vision demands that the eye make three adjustments: accommodation of
the lens, constriction of the pupils, and convergence of the eyeballs.
d. Myopia, or nearsightedness, occurs when objects focus in front of the retina and results in
seeing close objects without a problem but distance objects are blurred.
e. Hyperopia or farsightedness occurs when objects are focused behind the retina and results
in seeing distance objects clearly but close objects are blurred.
3. Photoreception is the process by which the eye detects light energy.
a. Photoreceptors are modified neurons that structurally resemble tall epithelial cells.
b. Rods are highly sensitive and are best suited to night vis ion. Cones are less sensitive to
light and are best adapted to bright light and colored vision.
c. Photoreceptors contain a light-absorbing molecule called retinal.
4. Stimulation of the Photoreceptors
a. The visual pigment of rods is rhodopsin and is formed and broken down within the rods.
b. The breakdown and regeneration of the visual pigments of the cones is essentially the same
as for rhodopsin.

3. 5. Exposure of the photoreceptors to light causes pigment breakdown, which hyperpolarizes the
receptors inhibiting the release of neurotransmitter conveying the information.
6. Light adaptation occurs when we move from darkness into bright light. Retinal sensitivity
decreases dramatically and the retinal neurons switch from the rod to the cone system.
7. Dark adaptation occurs when we go from a well-lit area into a dark one. The cones stop
functioning and the rhodopsin starts to accumulate in the rods increasing retinal sensitivity.
8. Visual Pathway to the Brain
a. The retinal ganglion cells merge in the back of the eyeball to become the optic nerve, which
crosses at the optic chiasma to become the optic tracts.
b. The optic tracts send their axons to neurons within the lateral geniculate body of the
thalamus.
c. Axons from the thalamus project through the internal capsule to form the optic radiation of
fibers in the cerebral white matter. These fibers project to the primary visual cortex in the
occipital lobes.
9. Visual processing occurs when the action of light on photoreceptors hyperpolarizes them,
which causes the bipolar neurons from both the rods and cones to ultimately send signals to
their ganglion cells.
II. The Chemical Senses: Taste and Smell (pp. 578–583; Figs. 15.21–15.24)
A. The receptors for taste and smell are chemoreceptors that respond to chemicals in solution.
B. The Olfactory Epithelium and the Sense of Smell (pp. 578–580; Figs. 15.21–15.22)
1. The olfactory epithelium is the organ of smell located in the roof of the nasal cavity.
2. The olfactory receptors are bipolar neurons with a thin apical dendrite that terminates in a
knob with several olfactory cilia.
3. To smell a particular odorant, it must be volatile and it must be dissolved in the fluid coating
the olfactory epithelium which stimulates the olfactory receptors.
4. In olfactory transduction, an odorant binds to the olfactory receptor, a G protein, and the
secondary messenger of cyclic AMP.
5. Axons of the olfactory receptor cells synapse in the olfactory bulbs sending impulses down
the olfactory tracts to the thalamus, the hypothalamus, amygdala, and other members of the
limbic system.
C. Taste Buds and the Sense of Taste (pp. 580–582; Figs. 15.23–15.24)
1. Taste buds, the sensory receptor organs for taste, are located in the oral cavity with the
majority located on the tongue.
2. Taste sensations can be grouped into one of five basic qualities: sweet, sour, bitter, salty, and
umami.
3. Physiology of taste
a. For a chemical to be tasted it must be dissolved in saliva, move into the taste pore, and
contact a gustatory hair.
b. Each taste sensation appears to have its own special mechanism for transduction.
4. Afferent fibers carrying taste information from the tongue are found primarily in the facial
nerve and glossopharyngeal cranial nerves.
5. Taste impulses from the few taste buds found on the epiglottis and the lower pharynx are
conveyed via the vagus nerve.
6. Taste is strongly influenced by smell and stimulation of thermoreceptors, mechanoreceptors,
and nociceptors.
D. Homeostatic Imbalances of the Chemical Senses

4. 1. Anosmias are olfactory disorders resulting from head injuries that tear the olfactory nerves,
nasal cavity inflammation, or aging.
2. Uncinate fits are olfactory hallucinations.
3. Taste disorders are less common but may be caused by respiratory tract infections, head
injuries, chemicals, medications, or head and neck radiation.
III. The Ear: Hearing and Balance (pp. 583–599; Figs. 15.25–15.38)
A. Structure of the Ear (pp. 583–589; Figs. 15.25–15.27)
1. The external ear consists of the auricle (pinna) and the external auditory canal, which is lined
with skin bearing hairs, sebaceous glands, and ceruminous glands.
2. The middle ear, or tympanic cavity, is a small, air-filled, mucosa-lined cavity in the petrous
portion of the temporal bone. It is spanned by the auditory ossicles.
3. The internal ear has two major divisions: the bony labyrinth and the membranous labyrinth.
a. The vestibule is the central cavity of the bony labyrinth with two membranous sacs
suspended in the perilymph, the saccule and the utricle.
b. The semicircular canals project from the posterior aspect of the vestibule, each containing
an equilibrium receptor region called a crista ampullaris.
c. The spiral, snail-shaped cochlea extends from the anterior part of the vestibule and contains
the cochlear duct, which houses the spiral organ (of Corti), the receptors for hearing.
B. Physiology of Hearing (pp. 587–593; Figs. 15.28–15.34)
1. Properties of Sound
a. Sound is a pressure disturbance produced by a vibrating object and propagated by the
molecules of the medium.
b. Frequency is the number of waves that pass a given point in a given time.
c. Amplitude, or height, of the wave reveals a sound’s intensity (loudness).
2. Airborne sound entering the external auditory canal strikes the tympanic membrane and sets it
vibrating.
3. The resonance of the basilar membrane processes sound signals mechanically before they
ever reach the receptors.
4. Transduction of sound stimuli occurs after the trapped stereocilia of the hair cells are deflected
by localized movements of the basilar membrane.
5. Impulses generated in the cochlea pass through the spiral ganglion, along the afferent fibers of
the cochlear nerve to the cochlear nuclei of the medulla, to the superior olivary nucleus, to the
inferior colliculus, and finally to the auditory cortex.
6. Auditory processing involves perception of pitch, detection of loudness, and localization of
sound.
C. Homeostatic Imbalances of Hearing (pp. 593–594)
1. Deafness is any hearing loss, no matter how slight.
2. Tinnitus is a ringing or clicking sound in the ears in the absence of auditory stimuli.
3. Ménière’s syndrome is a labyrinth disorder that causes a person to suffer repeated attacks of
vertigo, nausea, and vomiting.
D. Mechanisms of Equilibrium and Orientation (pp. 593–598; Figs. 15.35–15.38)
1. The equilibrium sense responds to various head movements and depends on input from the
inner ear, vision, and information from stretch receptors of muscles and tendons.
2. The sensory receptors for static equilibrium are the maculae.

5. 3. The receptor for dynamic equilibrium is the crista ampullaris, found in the ampulla of the
semicircular canals and activated by head movement.
4. Information from the balance receptors goes directly to reflex centers in the brain stem, rather
than to the cerebral cortex.
IV. Developmental Aspects of the Special Senses (pp. 598–599)
A. Embryonic and Fetal Development of the Senses
1. Smell and taste are fully functional at birth.
2. The eye begins to develop by the fourth week of embryonic development; vision is the only
special sense not fully functional at birth.
3. Development of the ear begins in the fourth week of fetal development; at birth the newborn is
able to hear but most responses to sound are reflexive.
B. Effects of Aging on the Senses
1. Around age 40 the sense of smell and taste diminishes due to a gradual loss of receptors.
2. Also around age 40 presbyopia begins to set in and with age the lens loses its clarity and
discolors.
3. By age 60 a noticeable deterioration of the organ of Corti has occurred; the ability to hear high-pitched
sounds is the first loss.
Cross References
Additional information on topics covered in Chapter 15 can be found in the chapters listed below.
1. Chapter 4: Epithelia; exocrine glands; connective tissues
2. Chapter 5: Sebaceous and sudoriferous glands
3. Chapter 8: Synovial joints
4. Chapter 10: Skeletal muscle naming
5. Chapter 11: Synapses; neurotransmitters
6. Chapter 12: Cerebral cortex; thalamus; CSF formation (similar to formation of aqueous humor)

6. 7. Chapter 13: Receptor and generator potentials; cranial nerves; reflex activity; chemoreceptors
8. Chapter 21: Inflammation
9. Chapter 22: Relationship between the auditory tube and the respiratory system
10. Chapter 23: Secretion of saliva and gastric juice; salivary reflex; papillae and taste buds
Laboratory Correlations
1. Marieb, E. N. Human Anatomy & Physiology Laboratory Manual: Cat and Fetal Pig Versions. Eighth
Edition Updates. Benjamin Cummings, 2006.
Exercise 24: Special Senses: Vision
Exercise 25: Special Senses: Hearing and Equilibrium
Exercise 26: Special Senses: Olfaction and Taste
2. Marieb, E. N. Human Anatomy & Physiology Laboratory Manual: Main Version. Seventh Edition
Update. Benjamin Cummings, 2006.
Exercise 24: Special Senses: Vision
Exercise 25: Special Senses: Hearing and Equilibrium
Exercise 26: Special Senses: Olfaction and Taste
Histology Slides for the Life Sciences
Available through Benjamin Cummings, an imprint of Pearson Education, Inc. To order, contac t your
local Benjamin Cummings sales representative.
Slide 77 Cochlea and the Organ of Corti, Inner Ear.
Slide 78 Retina of the Eye.
Slide 79 Taste Buds, Rabbit Tongue.
Slide 80 Cutaneous Receptors, Pacinian Corpuscle.
Slide 81 Olfactory Epithelium.
Slide 82 The Organ of Corti.
Slide 85 Section of a Monkey Eye.
Lecture Hints
1. Emphasize that each taste sensation is not localized to a specific area, but that there is significant
overlap of the different sensation areas. Students often assume that a particular point on the tongue
responds to a single type of substance.
2. Point out the importance of other sensations (especially smell) on the perception of taste.
3. During the lecture on olfactory anatomy, ask the class what would happen to olfaction if mucus glands
below the olfactory epithelium were absent.
4. Emphasize that olfactory receptors are the only renewable neurons in the body and are therefore the
one exception to the rule that neurons do not replicate.
5. There is often confusion in the terminology of the chambers of the eye. Point out that the anterior
segment is divided into anterior and posterior chambers by the iris.

7. 6. Initially, it is difficult for even the sharpest students to grasp the concept of ciliary muscle contraction
leading to lens thickening (for close focus). Intuitively, most think of the process of stretching the lens
as a consequence of muscle contraction, not relaxation. Spend some time reinforcing this concept.
7. Have students try out focusing on objects at night. Explain that they should not look directly at the
object, but slightly to one side, and the object should appear brighter. Relate this exercise to the
distribution of rods and cones in the eye.
8. As a point of interest, mention that the ossicles are joined by the smallest synovial joints in the body.
9. Emphasize the difference between static and dynamic equilibrium by comparing and contrasting the
anatomy of each type of equilibrium.
Activities/Demonstrations
1. Audio-visual materials listed under Multimedia in the Classroom and Lab.
2. Select four volunteers and spray a different strong cologne on their wrists. Then determine how long it
takes for each to “adapt” to the cologne.
3. Bring a convex lens to class and have students hold the glass up and focus on a distant object. They
will notice that it is upside down and reversed. Then explain that the human eye is also a single -lens
system. The question should arise: “Why don’t we see things upside down?”
4. Obtain a 3-D model of an eye and ear to illustrate the various anatomical parts of each.
5. Dissect a fresh (or preserved, if fresh is not available) beef eye to illustrate the anatomical structure and
nature of the tissues and fluids.
6. Obtain a skull to illustrate the locations of any bony structures associated with the senses.
7. Obtain a set of ear ossicles to illustrate how tiny they are.
Critical Thinking/Discussion Topics
1. Most people with sinus infections can’t smell or taste. Why?
2. Wine tasting can be a real art. Why are some people more adept at tasting than others? What effect
does smoking, alcohol, and/or sweets have on wine tasting? Why is it useful to swirl a glass of wine
and then sniff it?
3. Certain types of sunglasses can cause more harm than good. What could be wrong with inexpensive
sunglasses?
4. What would happen to gustatory and olfactory sensations if the receptors for taste and smell were
specific to a single substance?
5. Since the sclera is avascular, why do we see blood vessels in the white of the eye?
6. How is it possible that the cornea is transparent and the sclera is opaque when they are both
constructed of the same material and continuous with each other?
7. Examine the consequences to the anatomy of the eye and vision if aqueous humor drainage exceeded
production.
8. Explain why depth perception is lost if one eye is not functioning.
9. If the number of cones feeding into a single ganglion cell was increased tenfold, what would be the
consequence to color visual acuity?
10. Examine the consequences to sound perception if the tympanic membrane increased twofold in surface
area. What would happen if the oval window had increased surface area? Would sounds be perceived if
the round window became rigid?

8. Library Research Topics
1. How successful are cochlear implants? What surgical techniques are employed?
2. Some permanently deaf individuals have been helped by means of computers and electrical probes
connected to certain areas of the brain. How is this possible and what is the current research in this
area?
3. Contact lenses have long been used to correct vision problems. What is the status of contact lens
implants and why do ophthalmologists hesitate to perform them?
4. What substances are found in wines such as cabernet, chardonnay, chenin blanc, and ot hers that
provide the tremendous variety of tastes and smells?
5. If hearts, lungs, and livers can be transplanted, why not eyes? What would be some of the technical
difficulties?
Multimedia in the Classroom and Lab
Online Resources for Students
www.anatomyandphysiology.com www.myaandp.com
The following shows the organization of the Chapter Guide page in both the Anatomy & Physiology
Place and MyA&P™. The Chapter Guide organizes all the chapter-specific online media resources for
Chapter 15 in one convenient location, with e-book links to each section of the textbook. Please note that
®
both sites also give you access to other general A&P resources, like InterActive Physiology
, PhysioEx
6.0™, Anatomy 360°, Flashcards, a Glossary, a Histology Tutorial, and much more.
Objectives
Section 15.1 The Eye and Vision (pp. 556–578)
Art Labeling Activity: The Eye and Associated Accessory Structures (Fig. 15.1b, p. 557)
Art Labeling Activity: Internal Structures of the Eye (Fig. 15.4a, p. 560)
Case Study: Special Senses: Vision
Section 15.2 The Chemical Senses: Taste and Smell (pp. 578–583)
Memory: Eyesight Factors and the Art of Smelling
Section 15.3 The Ear: Hearing and Balance (pp. 583–598)
Art Labeling Activity: Structure of the Ear, Part 1 (Fig. 15.25a, p. 584)
Art Labeling Activity: Structure of the Ear, Part 2 (Fig. 15.25b, p. 584)
Memory: Sensory Organs
Section 15.4 Developmental Aspects of the Special Senses (pp. 598–599)
Chapter Summary
Self-Study Quizzes
Art Labeling Quiz
Matching Quiz
Multiple-Choice Quiz (Level I)
Multiple-Choice Quiz (Level II)
True-False Quiz
Crossword Puzzles
Crossword Puzzle 15.1

9. Crossword Puzzle 15.2
Media
See Guide to Audio-Visual Resources in Appendix A for key to AV distributors.
Video
1. The Eye: Vision and Perception (IM; 29 min., 1997). Highlights the structures and functions of the
mammalian eye and illustrates how visual sensory receptors relay messages to the brain.
2. How Sweet It Is: Tastes and Tasting (NIMCO; 22 min., 2001). From the Understanding our Five Senses
series. Provides an introduction to the sense of taste, shows how gustation works, and addresses the
role that smell plays in tasting.
3. The Nose Knows: Smelling and the Nose (NIMCO; 23 min., 2001). From the Understanding our Five
Senses series. Explores the olfactory organs, and discusses the molecular structure of odors and how
the brain interprets smells.
4. Sense Organs (IM; 24 min., 1994). Explores the anatomy and mechanism of the five senses.
5. The Senses (FHS; 20 min., 1995). From The New Living Body series, this program demonstrates how the
senses of sight and balance operate, as well as how they interact with each other.
6. Understanding the Senses (FHS; 56 min., 2000). Explores the beauty and complexity of visual, audial,
chemosensory, and tactile perception.
Software
®
InterActive Anatomy
1. A.D.A.M.
®
4.0 (see p. 9 of this guide for full lis ting).
®
MediaPro (see p. 9 of this guide for full listing).
2. A.D.A.M.
®
Anatomy Practice (see p. 86 of this guide for full listing).
3. A.D.A.M.
4. Bodyworks (see p. 9 of this guide for full listing).
5. Exploring Perception (TM; Win/Mac). Explores such phenomena as apparent movement, pitch
perception, sensory adaptation, and visual and auditory illusions.
6. The Ultimate Human Body (see p. 9 of this guide for full listing).
Lecture Enhancement Material
To view thumbnails of all of the illustrations for Chapter 15, see Appendix B.
Transparencies Index/Media Manager
Figure 15.1 The eye and associated accessory structures.
Figure 15.2 The lacrimal apparatus.
Figure 15.3 Extrinsic eye muscles.
Figure 15.4 Internal structure of the eye (sagittal section).
Figure 15.5 Pupil dilation and constriction, anterior view.
Figure 15.6 Microscopic anatomy of the retina.
Figure 15.7 Part of the posterior wall (fundus) of the right eye as seen with an ophthalmoscope.
Figure 15.8 Circulation of aqueous humor.
Figure 15.9 Photograph of a cataract due to a clouded lens.
Figure 15.10 The electromagnetic spectrum and photoreceptor sensitivities.
Figure 15.11 A spoon standing in a glass of water appears to be broken at the water-air interface.

10. Figure 15.12 Bending of light points by a convex lens.
Figure 15.13 Focusing for distant and close vision.
Figure 15.14 Problems of refraction.
Figure 15.15 Photoreceptors of the retina.
Figure 15.16 Sequence of chemical events in the formation and breakdown of rhodopsin.
Figure 15.17 Signal transmission in the retina.
Figure 15.18 Events of phototransduction.
Figure 15.19 Visual fields of the eyes and visual pathway to the brain, inferior view.
Figure 15.20 Responses of on-center and off-center retinal ganglion cells to different types of
illumination.
Figure 15.21 Olfactory receptors.
Figure 15.22 Olfactory transduction process.
Figure 15.23 Location and structure of taste buds on the tongue.
Figure 15.24 The gustatory pathway.
Figure 15.25 Structure of the ear.
Figure 15.26 The three auditory ossicles in the right middle ear.
Figure 15.27 Membranous labyrinth of the internal ear.
Figure 15.28 Anatomy of the cochlea.
Figure 15.29 Sound: source and propagation.
Figure 15.30 Frequency and amplitude of sound waves.
Figure 15.31 Route of sound waves through the ear.
Figure 15.32 Resonance of the basilar membrane and activation of the cochlear hair cells.
Figure 15.33 Photo of cochlear hair cells with their precise arrays of stereocilia.
Figure 15.34 Simplified diagram of the auditory pathway to the auditory cortex of the brain.
Figure 15.35 Structure of a macula.
Figure 15.36 The effect of gravitational pull on a macula receptor cell in the utricle.
Figure 15.37 Location and structure of a crista ampullaris.
Figure 15.38 Pathways of the balance and orientation system.
Answers to End-of-Chapter Questions
Multiple Choice and Matching Question answers appear in Appendix G of the main text.
Short Answer Essay Questions
30. The five basic tastes are sweet, sour, salty, bitter, umami. The sense of taste is served by the facial (VII),
glossopharyngeal (IX), and vagus (X) nerves. (p. 582)
31. The receptors are located in the roof of each nasal cavity. The site is poorly suited because air entering
the nasal cavities must make a hairpin turn to stimulate the receptors. (p. 578)
32. The nasolacrimal duct empties into the nasal cavity. (p. 557)
33. Rods are dim-light visual receptors, while cones are for bright-light and high-acuity color vision. (p. 563)
34. The fovea lies lateral to the optic disk. It contains only cones and provides detailed color vision for
critical vision. (p. 563)
35. Retinal changes to the all-trans form; the retinal-opsin combination breaks down, separating retinal and
opsin (bleaching). The net effect is to “turn off” sodium entry into the cell, effectively hyperpolarizing
the rod. (p. 572)

11. 36. Each cone responds maximally to one of these colors of light, but there is overlap in their absorption
spectra that accounts for the other hues. (p. 572)
37. With age, the lens enlarges, loses its crystal clarity and becomes discolored, and the dilator muscles of
the iris become less efficient. Atrophy of the organ of Corti reduces hearing acuity, especially for high -
pitched sounds. The sense of smell and taste diminish due to a gradual loss of receptors, thus appetite
is diminished. (pp. 598–599)
38. False. Each olfactory receptor cell is believed to have only one type of receptor protein (odorant
binding protein) that, however, responds to several different odorant molecules. (pp. 578–579)
Critical Thinking and Clinical Application Questions
1. Papilledema—a nipplelike protrusion of the optic disc into the eyeball, which is caused by conditions
that increase intracranial pressure. A rise in cerebrospinal fluid pressure caused by an intracranial tumor
will compress the walls of the central vein resulting in its congestion and bulging of the optic disc. (p.
600)
2. Pathogenic microoganisms spread from the nasopharynx through the pharyngotympanic tube into the
tympanic cavity. They may then spread posteriorly into the mastoid air cells via the mastoid antrum
resulting in mastoiditis, and medially to the inner ear, causing secondary labyrinthitis. If unchecked, the
infection may spread to the meninges, causing meningitis and possibly an abscess in the temporal lobe
of the brain or in the cerebellum. They may also invade the blood, causing septicemia. The cause of her
dizziness and loss of balance is a disruption of the equilibrium apparatus due to the labyrin thitis. (pp.
584–585)
3. Conjunctivitis. The foreign object probably would be found in the conjunctival sac near the orifice of
the lacrimal canals. (p. 557)
4. This is known as a detached retina. The condition is serious, but the retina can be reattached surgically
using lasers before permanent damage occurs. (p. 563)
5. The inability to hear high-pitched sounds is called presbycusis, a type of sensorineural deafness. It is
caused by the gradual loss of hearing receptors throughout life, but is accelerated if one is exposed to
loud rock music for extended periods. (p. 599)
6. Blindness, because visual impulses will be blocked from reaching the optic disk. (p. 575)
7. Albinism involves a hereditary inability for melanocytes to synthesize tyrosinase, an enzyme that is
needed for the production of melanin, a light-absorbing pigment that is normally present in the choroid
and the pigmented layer of the retina. A lack of melanin allows light scattering and reflection within the
eye, which causes visual confusion. (p. 569)
8. Jan had tinnitus. (p. 594)
9. This condition might be retinal detachment. (p. 563)
10. The chemotherapy could affect his sense of taste. (p. 583)
Suggested Readings
Barinaga, Marcia. “Smell’s Course Is Predetermined.” Science 294 (5545) (Nov. 2001): 1269–1271.
Berson, David M. “Phototransduction by Retinal Ganglion Cells that Set the Circadian Clock.” Science 295
(5557) (Feb. 2002): 1070–1073.
Cerio, Gregory. “Artificial Sight.” Discover 22 (8) (Aug. 2001): 50–54.
Daugman, John. “Iris Recognition.” American Scientist 89 (4) (July/August 2001): 326–333.
Firestein, Stuart. “How the Olfactory System Makes Sense of Scents.” Nature 413 (6852) (Sept. 2001): 211–
218.
Gagescu, Raluca. “Hear, Hear.” Nature Reviews: Molecular Cell Biology 2 (8) (Aug. 2001): 565.

12. Hattar, S. et al. “Melanopsin-Containing Retinal Ganglion Cells: Architecture, Projections, and Intrinsic
Photosensitivity.” Science 295 (5557) (Feb. 2002): 1065–1070.
Lindemann, B. “Receptors and Transduction in Taste.” Nature 413 (6852) (Sept. 2001): 219–225.
Nirenberg, S. M. et al. “Retinal Ganglion Cells Act Largely as Independent Encoders.” Nature 411 (6838)
(June 2001): 698–701.
Oliver, Dominik, et al. “Intracellular Anions as the Voltage Sensor of Prestin, the Outer Hair Cell Motor
Protein.” Science 292 (5525) (June 2001): 2340–2343.
Pichaud, Franck and Desplan, Claude. “A New View of Photoreceptors.” Nature 416 (6877) (March 2002):
139–140.
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