Lecture 02 Pain and Temperature Pathways Flashcards
What pathway conveys sharp, pricking, and highly-localized pain?
‘fast’ pain, direct spinothalamic pathway
pain and temperature
What pathway conveys burning pain, and deep, dull, aching, diffuse pain?
indirect spinothalamic system - slow pain
conveys more crude and diffuse type pain sensation
What are the primary fibers in the indirect spinothalamic pathway? where do they terminate?
unmyelinated type C fibers and send thousands of collateral terminals to nucleus proprius
some fibers may terminate in substantia gelatinosa and ascend in the direct spinothalamic system
What is the fasiculus proprius part of?
a diffuse neuronal net called the reticular formation which surrounds gray matter of the spinal cord and extends rostrally through the core of the brainstem to the thalamus
What does unilateral lesions of the spinoreticular fibers result in?
no in significant sensory deficits
the indirect spino-reticulo-thalamic pathway is too bilateral and diffuse to be affected by unilateral lesions
C fibers->nucleus proprius->spinoreticular fibers->fasiculus proprius ->reticular formation
what are spinoreticular fibers?
slow pain fibers from the nucleus proprius ascend to the thalamus as spinoreticular fibers
part of the indirect spinothalamic pathway
What is the general pattern of the direct spinothalamic pathway ?
Primary Neuron: spinal ganglion
Primary axon: enters the spinal cord, bifurcates and ascends and descends 2!!!! spinal cord segments
2dary neuron: in nucleus in the tip of the posterior horn of the spinal cord
2dary axon: decussate within 2 spinal cord lvls of incoming stimulus and ascend to specific nucleus in the dorsal thalamus
3tary neuron: in dorsal thalamus
3tary axons: project to postcentral gyrus - 1* somesthetic cortex
Where is the cell body of the secondary neuron in the direct spinothalamic pathway?
in the substantia gelatinosa
What do the axons of the secondary neurons int he direct spinothalamic pathway become?
they go through the anterior white commissure to form the lateral spinothalamic tract (LSTT) then the spinal lemniscus
Where are the cell bodies of the tertiary neurons in the direct spinothalamic pathway ?
VPL nucleus
What are cutaneous mechanoreceptors and thermal receptors innervated by?
Adelta sensory fibers: may respond to distortion or intense stimuli that is damaging to the skin
What are polymodal mechanoreceptors and thermal receptors innervated by?
C type sensory fibers: respond to noxious heat, chemical irritants applied to the skin and sunburn inflammation
What is the principal receptor for pain?
naked nerve endings int he epidermis
What are the receptors for thermal sensations ?
End bulbs of Krause
What is the main receptor for touch, pressure and kinesthesia?
Ruffini’s corpuscle
What are the primary neurons in the direct spinothalamic pathway? what is their course?
A delta and C fibers
Enter the spinal cord through the lateral division of the dorsal root and bifurcate to ascend and descend 2 segment in the dorsolateral fasciculus.
A delta fibers terminate on secondary neurons in the substantia gelatinosa
C fibers terminate on secondary neurons in nucleus proprius
Where is the substantia gelatinosa located?
at the tip of the dorsal horn of all lvls of the spinal cord
When does the LSTT become the spinal lemniscus?
in the medulla where its joins with VSTT and spinotectal tract
describe congenital absence of C type fibers
allows the nonnociceptive fibers to ‘close’ the gate
disinhibition of SG cells -> insensitivity to pain
Describe Herpes Zoster
Shingles infection may compromise the nonnociceptive A alpha/beta fibers
allow nociceptive C fibers to ‘open’ the gate
Increased sensitivity to pain from the sensory dermatome of the affected nerve
What does unilateral lesions of the lateral spinothalamic tract result in?
contralateral loss of pain and temperature sensation 2 sensory dermatomal segments below the lvl of the lesion
What is the treatment for intractable pain
anterolateral cordotomy
LSTT may be transected for the 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
Crude pain sensations usually remain intact
What is syringomyelia?
Defined as a gross cavitation and gliosis of the central canal usually occuring in the cervical regions of the spinal cord
The syrinx enlarges: deficits worsen over mnts and yrs
What parts of the spinal cord is affected by syringomyelia ?
Destruction of anterior white commissure: bilateral loss of pain and temp to upper extremities (yoke)
Asymmetrical destruction of lateral corticospinal tracts
Anterior horns destroyed: LMN paralysis with upper limb m
Posterior columns: ipsilateral anesthesia below lvl of lesion
What does the destruction of anterior horns result in?
LMN paralysis: flaccid paralysis, atrophy, areflexia and antonia
What does the destruction of posterior columns result in?
ipsilateral anesthesia proprioceptive and 2pth tactile sensations below the lvl of lesion
What does the destruction of the lateral corticospinal tracts result in?
spastic paralysis, hyperrreflexia, hypertonia of the lower extremity
What procedure causes a pt to be indifferent to, but very much aware of pain?
prefrontal lobotomy
pain perception also influenced by psychological and sociocultural biases expressed through limbic lobe and neocortex
