Pain and Temperature Pathways Flashcards Preview

Neuroscience I Test 3 > Pain and Temperature Pathways > Flashcards

Flashcards in Pain and Temperature Pathways Deck (19):
1

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

2

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

4

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

5

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

6

where is slow or visceral pain perceived?

thalamic level

7

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

8

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

9

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

11

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

12

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

19

syringomyelia

-gross cavitation and gliosis of the central canal occurring in the cervical regions of the SC
-as the syrinx enlarges, the neurological deficits progressively worsen over a period of months or years
-may occur secondary to central cord syndrome
-results in an abrupt onset of neurological deficits
-enlargement of the syrinx results in:
1. destruction of the anterior white commissure with a bilateral loss of pain and temp sensations to upper extremities
2. asymmetrical (unilateral or bilateral) destruction of the lateral corticospinal tracts results in spastic paralysis, hyperreflexia, hypertonia of lower extremity
3. anterior horns may be destroyed unilaterally or bilaterally which results in LMN paralysis (flaccid paralysis, atrophy, areflexia, atonia) of the assoc upper limb Ms
4. some part of posterior columns may be affected and result in ipsilateral anesthesia (proprioceptive and 2 point tactile sensations) below the level of the lesion