Download Lecture Suggestions and Guidelines

CHAPTER 12
NERVOUS SYSTEM III: SENSES
LEARNING OBJECTIVE 1: Name five kinds of receptors and explain the function of
each.
Lecture Suggestions and Guidelines
1. Introduce the major types of receptors, including chemoreceptors, pain receptors,
thermoreceptors, mechanoreceptors, and photoreceptors. Give an example of
each.
2. Describe the function of each major type of receptor based on its sensitivity to
changes in the environment.
3. Discuss the pathway from sensation to perception used to describe common
objects.
Application Question(s)
1. Ask students to give examples in the human body which demonstrate the major
types of sensory receptors.
Answer: Responses will vary, but should include examples of chemoreceptors,
pain receptors, thermoreceptors, mechanoreceptors, proprioreceptors,
baroreceptors, stretch receptors, and photoreceptors. Each of these types of
receptors is discussed in more detail throughout the chapter.
Critical Thinking Issue(s)
1. Ask each student to describe his/her favorite food in terms of the sense receptors
which are stimulated, stimulation of nerve fibers, impulse transmission to the
CNS, sensations (memories and experiences), and perception for the sense of
smell, taste, sight, and hearing.
Answer: Responses will vary, but students can use the information provided in
Table 12.1 regarding the information flow associated with an apple as a set of
guidelines.
LEARNING OBJECTIVE 2: Explain how receptors stimulate sensory impulses.
and
LEARNING OBJECTIVE 3: Explain how a sensation is produced.
Lecture Suggestions and Guidelines
1. Discuss how stimulation causes local changes in receptor potentials.
2. Define a sensory impulse and describe the transfer of receptor potentials to nerve
fibers triggering action potentials.
3. Reiterate information from Chapter 11 regarding the brain’s analysis and
interpretation of sensory impulses via peripheral nerves.
4. Define sensations.
5. Discuss the function of the sensory cortex in the interpretation of impulses, which
reach it.
6. Describe the process called projection, in which the brain projects the sensation
back to its region of stimulation.
7. Discuss sensory adaptation and give examples.
Application Question(s)
1. Ask students to explain the image they may continue to see shortly after they’ve
had their picture taken up close with a flash bulb camera.
Answer: The flash bulb light stimulates photoreceptors located on the retina,
which generates impulses to the brain. This perception is very intense and will last
for a short time after the actual stimulus has been removed.
Critical Thinking Issue(s)
1. Explain why, after amputation of a leg, a patient continues to feel pain and the
presence of the leg even though it is no longer there.
Answer: This phenomenon is known as phantom pain. It is the result of severed
nerve endings, which continue to send sensory nerve impulses even after the
amputation. The brain interprets these sensations as though the limb were still
present.
LEARNING OBJECTIVE 4: Distinguish between somatic and special senses.
Lecture Suggestions and Guidelines
1. Describe the three major groups of somatic senses, including exteroceptive
senses, proprioceptive senses, and visceroceptive senses.
2. Discuss the origins of somatic senses, i.e., skin, muscles, joints, and visceral
organs.
3. Briefly introduce the special senses, discussed in detail later, including the senses
of smell, taste, hearing, equilibrium, and sight.
4. Describe the origins of special senses, i.e., those whose receptors occur in
complex sensory organs of the head.
Application Question(s)
1. Give examples of specific locations in the human body where one might find
sensory nerve fibers, Meissner’s corpuscles and Pacinian corpuscles.
Answer: Sensory nerve fibers are common in epithelial tissues; Meissner’s
corpuscles are found in the lips, fingertips, palms, soles, nipples, and external
genital organs; Pacinian corpuscles are found in the deeper subcutaneous layers of
hands, feet, urethra, breasts, tendons of muscles, and ligaments of joints.
Critical Thinking Issue(s)
1. What causes color blindness?
Answer: The most common form of color blindness is red-green color blindness.
The genes regulating this sex linked inheritance are on the X chromosome; a male
with this gene on his one X chromosome will express the trait. It results in an
inability to distinguish certain colors, for which there is no cure. The defect
manifests itself in the cones located on the retina, which distinguish among red,
blue, and green wavelengths.
LEARNING OBJECTIVE 5: Describe the receptors associated with the senses of touch
and pressure, temperature, and pain.
Lecture Suggestions and Guidelines
1. Describe the free ends of sensory nerve fibers.
1. Introduce Meissner’s corpuscles and Pacinian corpuscles.
2. Discuss the functions of pain receptors.
2. Lecture on the location of pain receptors in the human body, and the changes to
which these receptors are sensitive.
3. Describe the two major types of thermoreceptors.
Application Question(s)
1. Provide students with a diagram of a section of the skin. Ask them to draw and
label cutaneous receptors to reiterate the information learned in Learning
Objective 5.
Answer: The diagram should include free nerve endings, Meissner’s corpuscles,
Pacinian corpuscles, Krause’s end bulb, Merkel’s disc, and Ruffini’s corpuscle,
all of which are found in the dermis.
Critical Thinking Issue(s)
1. Compare and contrast the information flow from the environment through the
nervous system for the senses of smell, taste, sight, and hearing.
Answer: The information flow begins with sense receptors, to stimulation of
nerve fibers, to impulse transmission toward the CNS, to sensation, and ends with
perception for each of the four senses mentioned above. The specifics for each
sense are summarized in the textbook.
LEARNING OBJECTIVE 6: Describe how the sense of pain is produced.
Lecture Suggestions and Guidelines
1. Lecture on the pain nerve pathways and the regulation of pain impulses.
2. Discuss referred pain.
3. Discuss enkephalins, serotonin, and endorphins in terms of pain suppression.
Application Question(s)
3. Ask students to research a current copy of the Physician’s Desk Reference to
prepare a report on a variety of anti-inflammatory drugs and muscle relaxants.
What are the drugs’ names, active ingredients, uses, contraindications, and side
effects.
Answer: This will give the students an opportunity to become familiar with the
PDR and will lend insight into Learning Objective 6.
Critical Thinking Issue(s)
1. Discuss a variety of methods for the alleviation of pain. Ask students to relate
examples from personal experience. Use the approached mentioned in Clinical
Application 12.1 as a guide, but keep an open mind toward suggestions given by
students which have been personally successful.
Answer: Responses will vary.
LEARNING OBJECTIVE 7: Explain the importance of stretch receptors in muscles
and tendons.
Lecture Suggestions and Guidelines
1. Discuss the actions of muscle spindles during muscle relaxation and during
muscle contraction. Include a discussion of how muscle spindles help maintain
posture.
2. Describe the location and function of Golgi tendon organs.
3. Introduce stretch reflex and give examples of this action.
Application Question(s)
1. Compare and contrast muscle spindles to Golgi tendon organs.
Answer: Muscle spindles—found in skeletal muscles, cause a stretch reflex,
which opposes the lengthening of a muscle. Golgi tendon organs—found in
tendons, stimulated by increased tension which inhibits muscle contraction.
Muscle spindles and Golgi tendon organs stimulate a reflex with opposite effects.
Critical Thinking Issue(s)
1. Discuss which somatic receptors would most likely be stimulated by the
following actions: a) cutting your finger with a knife; b) scraping the fingertips
over a hard-wire brush; c) placing your hand near an open flame; d) holding a
glass of ice water; e) lifting a dumb bell with one hand; f) detecting a mosquito
landing on your leg; g) holding tightly to an electric sander.
Answer: Use the textbook table to direct students’ discussions.
LEARNING OBJECTIVE 8: Explain the relationship between the senses of smell and
taste.
Lecture Suggestions and Guidelines
1. Describe the olfactory receptors and taste receptors as chemoreceptors, working
in conjunction to aid in food selection.
2. Lecture on the location and function of the olfactory and taste receptors.
3. Discuss factors that affect our sense of taste, including a heavy reliance upon
stimulation of olfactory receptors by aromas.
4. Introduce the four primary taste sensations and the location of each type of taste
receptor on the tongue.
5. Introduce the primary odors, and give examples of each.
6. Discuss the olfactory and taste nerve pathways.
Application Question(s)
1. Provide a variety of common edible samples to students. After students sample
each item, ask them to draw a “taste map” which illustrates the location of taste
buds on the tongue corresponding to the four basic taste sensations.
Answer: Responses will vary.
Critical Thinking Issue(s)
1. What drugs and medications alter our sense of taste and smell? Ask students to
recount specific examples from personal experience, and then discuss the
examples provided in Clinical Application 12-3 in the textbook.
Answer: Responses will vary.
LEARNING OBJECTIVE 9: Name the parts of the ear and explain the function of each
part.
Lecture Suggestions and Guidelines
1. Discuss the anatomy of the ear, including the major structures of the external,
middle, and inner ear.
1. Describe the major steps in the generation of sensory impulses from the ear.
2. Describe the mechanism of hearing, from the capture of sound waves by the
auricle to the interpretation of sound by the auditory cortex in the temporal lobe.
3. Discuss the auditory nerve pathways.
Application Question(s)
1. Provide a diagram of the external, middle, and inner ear and ask students to label
the major structures of each. Use models, overheads, and slides to reiterate these
structures.
Answer: N/A
Critical Thinking Issue(s)
1. Ask students to prepare a brief report on noise pollution. Schedule a site visit to a
local factory, plant, or construction site and have students report on their findings.
These observations should lead to discussions regarding major types of deafness,
including conduction, nerve, and central deafness.
Answer: N/A
LEARNING OBJECTIVE 10: Distinguish between static and dynamic equilibrium.
Lecture Suggestions and Guidelines
1. Discuss static equilibrium. Include a description of maculae, which provide
information on position of the head with respect to gravity, and otoliths, stones of
calcium salts embedded in a gel-like substance which stimulate the maculae by
their movement.
2. Define doll’s eyes reflex.
3. Describe dynamic equilibrium, which responds to angular movements of the head.
Include in the description a discussion of the crista ampullaris and cupula.
4. Discuss ancillary structures, which help to maintain equilibrium.
Application Question(s)
1. Ask students to recall a recent boat ride, dance in which they were twirled around,
amusement park ride that involved twirling and turning upside down, or an
experience of reading for a extended period of time while riding in a car. Have
them relate this experience in terms of the effects upon dynamic equilibrium
receptors, and explain what causes the reversed motion sensation when they
stopped the activity.
Answer: Responses will vary, but should include a discussion of the crista
ampullaris, cupula, and stimulation of the hair cells.
Critical Thinking Issue(s)
1. Explain doll’s eyes reflex, observed when an infant is tilted backward, or the head
is moved to the right or left.
Answer: Doll’s eyes reflex is a compensation for a disturbance in balance and
equilibrium. The eyes actually roll downward, left, or right, so that the gaze will
remain fixed. It is a normal reflex, which disappears as ocular fixation matures.
LEARNING OBJECTIVE 11: Name the parts of the eye and explain the function of
each part.
Lecture Suggestions and Guidelines
1. Describe the three major tunics of the eye; the sclera, choroid coat, and retina.
2. Discuss the anatomy and physiology of the lens, iris, aqueous and vitreous
humors, pupil, cornea, conjunctiva, lacrimal gland, sclera, and optic nerve.
3. Introduce the names and functions of six muscles, which move the eye in various
directions.
4. Describe the pathway of light entering the eye to the retina.
Application Question(s)
1. Provide students with a diagram of the human eye and ask them to label the
structures discussed in lecture and in the textbook. Reinforce their knowledge by
performing dissections on commercially prepared specimens.
Answer: N/A
Critical Thinking Issue(s)
1. What causes glaucoma?
Answer: Aqueous humor provides nutrients to several structures of the eye,
which lack their own blood supply. This fluid must be allowed to drain through
the canal of Schlemm to be reabsorbed into the bloodstream. If the canal of
Schlemm is blocked, drainage cannot occur, pressure builds, and the retina and
optic nerve become compressed, causing pain and blindness. Glaucoma can be
treated with miotics.
LEARNING OBJECTIVE 12: Explain how the eye refracts light.
Lecture Suggestions and Guidelines
1. Introduce the term refraction and illustrate the concept by demonstrating the
bending of light rays through a plate of glass or water.
2. Compare the emmetropic, myopic, and hyperopic eye and introduce lenses, which
could be used to correct these conditions. Also, define astigmatism.
3. Describe the role of rhodopsin.
4. Discuss two major photoreceptors, rods and cones, and explain the function of
each.
5. Describe how a real image is formed on the retina.
Application Question(s)
1. Conduct a survey of the students to determine how many are myopic, hyperopic,
have astigmatism, or a combination of two or more. Proceed with a discussion of
corrective lenses, e.g., concave, convex, bifocal, trifocal, etc.
Answer: You may be surprised to find how many students know they have an
eye-focusing disorder, but aren’t sure of the definitions of near-sightedness, farsightedness, and astigmatism. The physics of how their synthetic lenses correct
for deficiencies may also be a new concept.
Critical Thinking Issue(s)
1. Discuss the probable causes and effects of hemianopia.
Answer: Hemianopia, or hemiamblyopia, is defective vision or blindness in one
half of the visual field. It is somewhat common in patients who have experienced
a stroke, resulting in damage to the visual cortex on one side. Therefore, the
patient would not be able to see things on the nonfunctional side of the visual
field.
LEARNING OBJECTIVE 13: Explain how the brain perceives depth and distance.
Lecture Suggestions and Guidelines
1. Introduce stereoscopic vision.
2. Describe how stereoscopic vision occurs via superimposed images.
3. Discuss the compensation made by a one-eyed person to judge distance and
depth.
Application Question(s)
1. As a result of several blows to the face and head, a boxer experienced a detached
retina. What had taken place inside the eye? Could it be repaired?
Answer: Perforations caused by trauma to the posterior chambers of the eye
result in a leakage of vitreous humor, and a subsequent decrease in intraocular
pressure. The retina may then detach from the posterior wall or be torn away by
repeated traumatic occurrences.
Critical Thinking Issue(s)
1. Ask students to research the developmental aspects of vision in newborns.
Compare these findings with adult vision.
Answer: A baby’s eyeball continues to enlarge until approximately nine years
old. Newborns are hyperopic. Color vision is underdeveloped, newborns seeing
primarily in gray tones. Visual acuity is poor, but depth perception, color vision,
and visual acuity are greatly improved by the age of five.
LEARNING OBJECTIVE 14: Describe the visual nerve pathway.
Lecture Suggestions and Guidelines
1. Describe the visual pathway from the eye to the brain. Include a description of the
optic chiasma, optic tracts, and optic radiation.
2. Discuss the overlapping of visual fields and the sites on the retina where a real
image would be focused.
3. Describe how each eye “sees” a slightly different view.
Application Question(s)
1. What causes eyestrain?
Answer: Eyestrain is often caused by extended periods of reading or tasks, which
require intense scrutiny (such as watch repair). The extrinsic muscles converge,
the ciliary body muscles bulge the lens, and the constrictor muscles of the pupil
provide acute vision through the accommodation photopupillary reflex.
Critical Thinking Issue(s)
1. Ask students to prepare a brief report addressing the effects of aging on vision.
Answer: Reports will vary, but should include a discussion of presbyopia, the
functioning of the lacrimal glands, loss of lens clarity, susceptibility to bacterial
infections, muscle inefficiency, higher incidence of cataracts and glaucoma, and
the secondary effects of diabetes, strokes, hypertension, cancer, and other diseases
associated with the process of aging.
RELATED DISEASES OF HOMEOSTATIC INSTABILITY
1. Otitis Externa—Commonly referred to as “swimmer’s ear,” it is caused by a
fungal or bacterial infection of the ear canal. It may develop in the presence of
highly chlorinated swimming pools, excessive moisture in the ear, or by
swimming in dirty, polluted water.
2. Cararact—A non-cancerous clouding of the lens of the eye. It may be caused by
inefficient nourishment from the vitreous humor. Cataracts are usually curable
with surgery.
3. Glaucoma—A blockage of the fluid-draining mechanism of the eye, resulting in
blurred vision or loss of peripheral vision. Chronic glaucoma is usually treatable
with medications, diuretics, and smoking cessation.
SUGGESTIONS FOR ADDITIONAL READING
Freedman, David. June 1993. In the realm of the chemical. Discover. Smell and taste
have helped us navigate a world of fowl poisons and sweet, voluptuous pleasures.
Gilbert, Avery N., and Charles J. Wysocki. October 1987. The smell survey. National
Geographic. In fall 1986, 1.5 million Americans filled out a scratch-and-sniff survey
on what they could and could not smell. Results are illuminating.
Gorman, Jessica. August 31, 2002. Germ Fighter–Lens coating may keep contacts in eye
longer. Science News.
Grady, Denise. June 1993. The vision thing: mainly in the brain. Discover. The eye and
brain work in a partnership to interpret conflicting signals from the outside world.
Gutin, JoAnn. June 1993. Good vibrations. Discover. We’re under siege from age, drugs,
and rock ‘n’ roll, and all that stands between us and utter silence is 32,000 dancing
hearing receptors.
Kennedy, John M. January 1997. How the Blind Draw. Scientific American.
Lewis, Ricki. November 1991. FDA Consumer. When smell and taste go awry. It is hard
to imagine life without the chemical senses.
McLaughlin, Susan K., et al. June 18, 1992. Gustducin is a taste-cell-specific G protein
closely related to the transducins. Nature, vol. 357. A molecular look at the sense of
taste.
Reed, Randall R. January 12, 1990. How does the nose know? Cell, vol. 60. At the
molecular level, the sense of smell is a manifestation of signal transduction.
Shreeve, James. June 1993. Touching the phantom. Discover. Amputees can feel missing
hands grab a cup of coffee, missing feet itch, and missing legs ache. Behind these
ghostly sensations lies the secret of touch.
Zimmer, Carl. June 1993. Making senses. Discover. Can electronic devices make the
blind see, the deaf hear?