C h a p t e r 3 5
Somatosensory Function, Pain, and Headache
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lateral thalamus and the somatosensory cortex are neces-
sary to add precision, discrimination, and meaning to the
pain sensation. The paleospinothalamic system projects
diffusely from the intralaminar nuclei of the thalamus to
large areas of the limbic cortex. These connections prob-
ably are associated with the hurtfulness and the mood-
altering and attention-narrowing effect of pain.
Recent research has demonstrated cortical repre-
sentation of fast–sharp and slow–chronic types of pain
sensation. In healthy adults, nociceptive A
δ
afferent stim-
ulation is related to activation in the contralateral pri-
mary somatosensory cortex in the parietal lobe, whereas
C afferent stimulation is related to activation of the sec-
ondary somatosensory cortices and the anterior cingu-
lated cortex, which is part of the limbic system. With both
afferents there is activation of the bilateral secondary
somatosensory cortices in the posterior parietal lobes.
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Central Pathways for Pain Modulation
A major advance in understanding pain was the discov-
ery of neuroanatomic pathways that arise in the mid-
brain and brain stem, descend to the spinal cord, and
modulate ascending pain impulses. One such pathway
Thalamus
Somesthetic association cortex
Limbic cortex
Emotional experience
Pontine
noradrenergic neurons
Primary somesthetic cortex
Discrimination, location, intensity
Thalamus
A-delta
(fast)
C-fiber
(slow)
Neospinothalamic tract
(sharp, bright pain)
Paleospinothalamic tract
(dull, aching pain)
Spinal cord and dorsal horn
modulating circuits
Perception and meaning
Cognition, anxiety, insomnia
Hypothalamus
Autonomic and
endocrine responses
Midbrain
periaqueductal gray
Endogenous
analgesic center
Medullary nucleus
raphe magnus
Brain stem RAS
Increased alertness
Dorsal root
ganglia
Nociceptive stimuli
Cortical centers
Primary touch fibers
FIGURE 35-8.
Primary pain pathways.The transmission of incoming nociceptive impulses is
modulated by dorsal horn circuitry that receives input from primary touch receptors and from
descending pathways that involve the limbic cortical systems (orbital frontal cortex, amygdala,
and hypothalamus), the periaqueductal endogenous analgesic center in the midbrain, pontine
noradrenergic neurons, and the nucleus raphe magnus (NRM) in the medulla. Dashed lines indicate
inhibition or modulation of pain transmission by dorsal horn projection neurons. RAS, reticular
activating system.
