Flashcards in Pain and Temperature Pathways Deck (19)
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indirect spinothalamic pathway
-slow/crude pain
-diffuse pain
-Rs are assoc with viscera and is described as burning, deep, dull, aching poorly localized
-C type fibers-->nucleus proprius-->fasciculus proprius in the reticular formation-->centromedian nucleus in the hypothalamus
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primary neurons in the indirect spinothalamic pathway
-unmyelinated C fibers with a very slow conduction rate
-when they enter the SC, they bifurcate and ascend and descend a variable numbers of segments in the dorsolateral fasciculus of Lissaur
-primary fibers send collateral terminals to the nucleus proprius
-some fibers from the C type fibers may also go to the substantia gelatinous and ascend in the direct spinothalamic system
-visceral or slow pain may be perceived as somatic or fast pain if enough C type fibers recruited which allows info to go to the direct spinothalamic pathway
3
secondary neurons in the indirect spinothalamic pathway
-come from the nucleus proprius and course bilaterally in the anterior, lateral, and posterior regions of the fasciculus proprius
-most fibers terminate on interneurons which will form the neuronal patterns for the complex, stereotyped intersegmental reflexes characteristic of pain responses
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spinoreticular fibers
-slow pain info from the nucleus proprius may ascend to the thalamus as spinoreticular fibers
-these fibers are part of a divergent, multi neuronal polysynaptic pathway and embedded in the anterior, lateral, and posterior regions of the fasciculus proprius
-ultimately terminate in the midline reticular formation of the brainstem, hypothalamus, and centromedian nucleus of the dorsal thalamus on both sides of the brain
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fasciculus proprius
-part of a diffuse neuronal net called the reticular formation which surrounds the gray matter of the SC and extends rostrally thru the core of the brainstem to the thalamus
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where is slow or visceral pain perceived?
thalamic level
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unilateral lesions of the spinoreticular fibers vs bilateral lesions
-do not result in significant sensory defects
-the indirect spinothalamic pathway is too bilateral and diffuse to be affected by unilateral lesions
-bilateral lesions such as SC transactions may eliminate crude pain sensations
-if the transection is incomplete or at different levels, the spinoreticular fibers may find a route thru the intact portion of the fasciculus proprius which is the basis of persistent or intractable pain
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direct spinothalamic pathway
-fast pain
1. primary neuron--located in the spinal ganglion
-primary axon enters the SC, bifurcates, and ascends/descends 2 SC segments
2. secondary neuron--located in a nucleus in the tip of the posterior horn of the SC
-secondary axons: decussate within 2 SC levels of the incoming stimulus and ascend to a specific nucleus in the dorsal thalamus
3. tertiary neuron--located in the dorsal thalamus
-tertiary axons: project to the post central gyrus which is referred to as the primary somesthetic cortex
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primary neurons of the direct spinothalamic pathway
-in the spinal ganglia
-send central processes into the SC
-primary axon enters the SC, bifurcates, and ascends/descends 2 SC segments
-2 types: A delta and C
-the axons of both enter the SC thru the lateral division of the dorsal root, and bifurcate to ascend and descend +/- 2 segments in the dorsolateral fasciculus
-these fibers terminate on secondary neurons in the substantia gelatinosa (A delta) and nucleus proprius (C)
-with a lesion here, we would get contralateral loss of pain and temp 2 sensory dermatomes away from the lesion
10
secondary neurons of the direct spinothalamic pathway
-in the substantia gelatinosa
-send axons thru the anterior white commissure to form the lateral spinothalamic tract (LSTT)
-secondary axons: decussate within 2 SC levels of the incoming stimulus and ascend to a specific nucleus in the dorsal thalamus
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tertiary neurons of the direct spinothalamic pathway
-in the VPL nucleus of the thalamus
-tertiary axons: project to the post central gyrus which is referred to as the primary somesthetic cortex
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reticular formation
-from the thalamus
-contain the fasciculus proprius
-role in consciousness/arousal
-original sensory/motor integration
-"battery of cortex"
13
congenital absence of C type fibers
-allows the non-nociceptive fibers to close the gate
-person is insensitive to pain
14
Herpes Zoster
-Herpes Zoster (shingles) infection may compromise the non-nociceptive A alpha/beta fibers, thereby allowing the nociceptive (C) fibers to open the gate
-person has an inc sensitivity to pain from the sensory dermatome of the affected N
15
unilateral lesions of the lateral spinothalamic tract
-result in a contralateral loss of pain and temp sensation 2 sensory dermatomal segments below the level of the lesion
-problem with the direct spinothalamic pathway
16
treatment of intractable pain
-LSTT may be transected for relief of intractable pain
-the anterolateral quadrant of the cord is cut 2 segments above and on the opposite side of the area of pain
-procedure is called the anterolateral cordotomy or tractotomy
-the denticulate ligaments serve as landmarks b/w the LSTT (anteriorly) and the corticospinal fibers (posteriorly)
-crude pain sensations usually remain intact or are only temporarily diminished
17
unilateral lesions of the spinal lemniscus in the direct spinothalamic pathway
-result in contralateral hemianalgesia and thermal hemianesthesia
18
prefrontal lobes and the prefrontal lobotomy
-prefrontal lobes play an important role in the emotional importance and response we have to pain
-pts with intractable pain used to have fibers from the prefrontal lobes surgically disconnected from the remaining hemispheres in a prefrontal lobotomy
-the pt loses the anxiety and emotional component that is so often assoc with pain
-pain is indifferent to pain but aware of pain
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