Sensory Physiology
231
Patient
1.
The left half of the visual field
of each eye would be dark
because neurons from the
right half of each of the retinas
would not reach the visual cortex.
2.
The outer half of the visual
field seen by each eye would
be dark because neurons from
the inner half of the retinas that
cross at the optic chiasm would
not reach the visual cortex.
3.
The right half of the visual field
seen by each eye would be
perceived as dark because the
left occipital lobe processes
neuronal input from the left
half of each retina.
Left Eye
Right Eye
Chapter 7 Quantitative and Thought Questions
(Answers appear in Appendix A.)
1. Describe several mechanisms by which pain could theoretically
be controlled medically or surgically.
2. At what two sites would central nervous system injuries
interfere with the perception that heat is being applied to the
right side of the body? At what single site would a central
nervous system injury interfere with the perception that heat is
being applied to either side of the body?
3. What would vision be like after a drug has destroyed all the
cones in the retina?
4. Damage to what parts of the cerebral cortex could explain the
following behaviors? (a) A person walks into a chair placed in
her path. (b) The person does not walk into the chair, but she
does not know what the chair can be used for.
Chapter 7 Answers to Physiological Inquiries
Figure 7–2
Receptor potentials would not be affected because
they are not mediated by voltage-gated channels. Action
potential propagation to the central nervous system would also
be normal because it depends only on voltage-gated sodium and
potassium channels.
The drug would inhibit neurotransmitter
release from the central axon terminal, however, because
vesicle exocytosis requires calcium entry through voltage-gated
channels.
Figure 7–6b
Although the skin area of your lips is much smaller
than that of your back, the much larger number of sensory
neurons originating in your lips requires a larger processing
area within the somatosensory cortex of your brain.
See
Figure 7–20 for a diagrammatic representation of cortical areas
involved in sensory processing.
Figure 7–19
Sensation of all body parts above the level of the
injury would be normal.
Below the level of the injury, however,
there would be a mixed pattern of sensory loss.
Fine touch,
pressure, and body position sensation would be lost from
the left side of the body because that information ascends in
the spinal cord on the side that it enters without crossing the
midline until it reaches the brainstem.
Pain and temperature
sensation would be lost from the right side of the body below
the injury because those pathways cross immediately upon entry
and ascend in the opposite side of the spinal cord.
Figure 7–29
Figure 7–30b
Most people who stare at the yellow background,
perceive an after-image of a blue circle around the square.
This
is because prolonged staring at the color yellow activates most
of the available retinal in the photopigments of both red and
green cones (see Figure 7–30a), effectively fatiguing them
into a state of reduced sensitivity.
When you shift your gaze
to the white background (white light contains all wavelengths
of light), only the blue cones are available to respond, so you
perceive a blue circle until the red and green cones recover.
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