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SOMATIC SENSORY SYSTEM
I. TRUE or FALSE. Circle the T or F as appropriate.
T F 1. Endogenous regulation of pain signals involves a "gating" mechanism in the
substantia gelatinosa.
T F 2. The largest diameter sensory fibers innervate muscle spindles and tendon
organs, but not the skin.
T F 3. Group III afferent fibers mediate slow pain.
T F 4. Some of the primary sensory fibers entering the pons with the trigeminal nerve
make synapses in the lower medulla.
T F 5. All Group III and IV sensory fibers terminate as free nerve endings.
T F 6. At the level of the upper medulla, the medial lemniscus is found near the
midline, medial to the inferior olive.
II. MULTIPLE CHOICE. Circle every correct answer. There may be more than one
correct answer per question.
1. Relatively high cutaneous receptor density is found in
a. the skin of the back of the neck
b. the skin of the lips
c. skin receiving an exaggerated cortical representation (i.e., relatively high
cortical magnification)
d. skin whose primary cutaneous afferents have relatively large receptive fields
e. skin in which two-point discrimination thresholds are relatively low (i.e., spatial
acuity is good)
2. Free nerve endings can serve as receptors for the sensations of
a.
b.
c.
d.
e.
fast pain
touch
warmth
cold
slow pain
3. A dissociated sensory loss (a loss affecting some somatic sensory submodalities and
not others) could arise from
a.
b.
c.
d.
e.
destruction of dorsal root ganglia
destruction of the precentral gyrus
a lesion restricted to the dorsal columns
an infarction affecting the midline of the medulla
a disease process interrupting the anterolateral quadrant of the spinal white
matter
4. Highly discrete localization of cutaneous stimuli is mediated in part by the
a.
b.
c.
d.
e.
anterolateral system
spinal trigeminal nucleus
dorsal column-medial lemniscus system
main (principal) nucleus of the fifth cranial nerve
lateral lemniscus
5. At the level of the medulla, fibers of the spinothalamic tract
a.
b.
c.
d.
e.
lie lateral to the fibers of the medial lemniscus
make synapses in the reticular formation
have arisen from cells in the dorsal column nuclei
have arisen from cells in the dorsal horn of the spinal cord
decussate (cross the midline)
6. Gating of pain impulses by the central nervous system occurs first in the
a.
b.
c.
d.
e.
dorsal column nuclei
substantia gelatinosa
dorsal root ganglion
dorsal nucleus of Clarke
anterior white commissure
7. The perceptual quality or modality associated with activity in a particular nerve fiber
is determined by
a.
b.
c.
d.
e.
the physical nature of the stimulus
the specialization of the receptor endings
the degree of myelinization of the nerve fiber
the central connections of the nerve fiber
the duration of action potentials in the nerve fiber
8. Cutaneous nerve fibers selectively sensitive to temperature
a.
b.
c.
d.
e.
are all myelinated
are all unmyelinated
terminate peripherally as free nerve endings
terminate peripherally as Pacinian corpuscles
synapse centrally in the dorsal horn of the spinal cord
9. Two point discrimination is most acute, i.e. the resolvable points are closest together,
in regions of skin
a.
b.
c.
d.
e.
having the highest receptor density
innervated by fibers with the broadest distribution of sensory terminals
innervated by Group I (A alpha) afferents
associated with the smallest receptive fields among cells in the postcentral gyrus
having the most largest magnification in somatic sensory cortex
10. Primary sensory fibers enter the spinal cord
a.
b.
c.
d.
e.
via the dorsal roots
via the ventral roots
via the internal capsule
via the cauda equina
via the thalamus
11. The ability to make fine discriminations in the position of the right arm would be lost
following damage to
a.
b.
c.
d.
e.
the spinal roots on the left at cervical levels
the spinal roots on the right at thoracic levels
the dorsal columns on the right at upper cervical levels
the ventral posterior nucleus of the left thalamus
the medial lemniscus on the left side of the brainstem
12. "Fast" and "slow" pain are mediated respectively by
a.
b.
c.
d.
e.
group A-delta and group C afferents
group III and group IV afferents
large and small unmyelinated fibers
dorsal columns and spinothalamic tracts
neospinothalamic and archispinothalamic projections
13. In the skin's response to injury (triple response of Lewis), an axon reflex (antidromic
impulse propagation down branches stimulated afferents) appears to be responsible
for the
a.
b.
c.
d.
e.
local swelling of the skin
pain
flare (widespread vasodilation)
local reddening
placebo effect
14. Soap gets in your right eye. Which of the following structures participate in the
sensation of pain that results?
a.
b.
c.
d.
e.
optic nerve
trigeminal nerve
main sensory nucleus of fifth nerve
spinal nucleus of fifth nerve
ventral posteromedial nucleus of the thalamus
15. Electrical stimulation in the periaqueductal grey causes analgesia via a pathway
a.
b.
c.
d.
e.
in which endogenous opioid compounds are involved
involving the nucleus raphe magnus and dorsolateral columns
involving the corticospinal tract and intermediolateral cell column
in which serotonergic cells participate
probably involved in the analgesic placebo effect
16. The first synapse in the main spinal pathway for epicritic sensation occurs
a.
b.
c.
d.
e.
in the spinal cord
in the dorsal columns
in the dorsal column nuclei
in the medulla
in the thalamus
17. The first synapse in the spinal pathways for protopathic sensation occurs
a.
b.
c.
d.
e.
in the dorsal root ganglia
in the dorsal horn
in the anterolateral funiculus
in the zone of Lissauer
in the medulla
18. Neurons in the dorsal column nuclei (nucleus gracilis and nucleus cuneatus) emit
axons that can be found in
a.
b.
c.
d.
e.
the medial lemniscus
the medial longitudinal fasciculus
the medulla
the pons
the midbrain
SOMATIC SENSORY
I. True or False
1.
2.
3.
4.
5.
6.
T
T
F
T
T
T
II. Multiple Choice
1.
2.
3.
4.
5.
6.
7.
b, c, e
a, b, c, d, e
c, d, e
c, d
a, b, d
b
d
8. c, e
9. a, d, e
10. a, b, d
11. c, d, e
12. a, b, e
13. c
14. b, d, e
15.
16.
17.
18.
a, b, d, e
c, d
b
a, c, d, e