HUMAN BIOLOGY

284 Chapter 14

6. Detecting substances present in the body fluids that bathe
   them is the function of.
   a. thermoreceptors c. mechanoreceptors
   b. photoreceptors d. chemoreceptors


7. Which of the special senses is based on the following
   events? Membrane vibrations cause fluid movements,
   which lead to bending of mechanoreceptors and firing
   of action potentials.
   a. taste c. hearing
   b. smell d. vision


8. Rods differ from cones in the following ways:
   a. They detect dim light, not bright light.
   b. They have a different visual pigment.
   c. They are not located in the retina.
   d. All of the above.
   e. a and b only


9. The outer layer of the eye includes the.
   a. lens and choroid c. retina
   b. sclera and cornea d. both a and c


10. The inner layer of the eye includes the.
    a. lens and choroid c. retina
    b. sclera and cornea d. start of optic nerve


11. Your visual field is.
    a. a specific, small area of the retina
    b. what you actually “see”
    c. the area where color vision occurs
    d. where the optic nerve starts


12. Match each of the following terms with the appropriate
    description.
    somatic senses a. produced by strong
    (general senses) stimulation
    special senses b. endings of sensory
    variations in neurons or specialized
    stimulus intensity cells next to them
    action potential c. taste, smell, hearing,
    sensory receptor balance, and vision
    d. frequency and number
    of action potentials
    e. touch, pressure,
    temperature, pain,
    and muscle sense

CritiCaL tHinKing

1. Juanita started having bouts of dizziness. Her doctor asked
   her whether “dizziness” meant she felt lightheaded as
   if she were going to faint, or whether it meant she had
   sensations of vertigo—that is, a feeling that she herself
   or objects near her were spinning around. Why was this
   clarification important for the diagnosis?


2. Michael, a 3-year-old, experiences a chronic middle-ear
   infection, which is common among youngsters, in part due
   to an increase in antibiotic-resistant bacteria. This year,
   despite antibiotic treatment, an infection became so advanced
   that he had trouble hearing. Then his left eardrum ruptured
   and a jellylike substance dribbled out. The pediatrician told
   Michael’s parents not to worry, that if the eardrum had not
   ruptured on its own she would have had to drain it. Suggest
   a reason why the physician concluded that this procedure
   would have been necessary to cure Michael’s problem.

Figure 14.25 Dangling upside down affects

several organs of equilibrium. What are they?

© Greg Epperson/Shutterstock.com

Recently a team of

researchers at the University

of Florida and University of

Pennsylvania reported they

had successfully used gene

therapy to restore vision in mice that had become blind as the

result of a genetic disease called X-linked retinitis pigmentosa.

Humans also can inherit this disease, in which a defective gene

causes rods and cones in the retina to degenerate. The defect

is passed from a carrier mother to male children who inherit an

affected X chromosome. Affected boys usually are blind by the

time they reach young adulthood. The experimental treatment

involved using a virus to insert working copies of the gene into

the blind mice. After other steps turned on the genes, the mice

gradually regained their eyesight. Although much remains to be

done before the treatment can be approved for use in humans,

researchers are cautiously optimistic that in time gene therapy

may help children born with X-linked retinitis pigmentosa to

regain at least some of their sight.

your Future

© Stan Sholik/Alamy

3. Jill is diagnosed with sensorineural deafness, a disorder
   in which sound waves are transmitted normally to the
   inner ear but they are not translated into neural signals
   that travel to the brain. Sometimes the cause is a problem
   with the auditory nerve, but in Jill’s case it has to do with a
   problem in the inner ear itself. Where in the inner ear is the
   disruption most likely to be located?


4. Larry goes to the doctor complaining that he can’t see
   the right side of the visual field with either eye. Where in
   the visual signal-processing pathway is Larry’s problem
   occurring?


5. In a rock climber like the man pictured in Figure 14.25,
   which organs of equilibrium are activated?

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