Lecture 02 Pain and Temperature Pathways

Question 1

What pathway conveys sharp, pricking, and highly-localized pain?

Answer 1

‘fast’ pain, direct spinothalamic pathway

pain and temperature

Question 2

What pathway conveys burning pain, and deep, dull, aching, diffuse pain?

Answer 2

indirect spinothalamic system - slow pain

conveys more crude and diffuse type pain sensation

Question 3

What are the primary fibers in the indirect spinothalamic pathway? where do they terminate?

Answer 3

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

Question 4

What is the fasiculus proprius part of?

Answer 4

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

Question 5

What does unilateral lesions of the spinoreticular fibers result in?

Answer 5

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

Question 6

what are spinoreticular fibers?

Answer 6

slow pain fibers from the nucleus proprius ascend to the thalamus as spinoreticular fibers

part of the indirect spinothalamic pathway

Question 7

What is the general pattern of the direct spinothalamic pathway ?

Answer 7

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

Question 8

Where is the cell body of the secondary neuron in the direct spinothalamic pathway?

Answer 8

in the substantia gelatinosa

Question 9

What do the axons of the secondary neurons int he direct spinothalamic pathway become?

Answer 9

they go through the anterior white commissure to form the lateral spinothalamic tract (LSTT) then the spinal lemniscus

Question 10

Where are the cell bodies of the tertiary neurons in the direct spinothalamic pathway ?

Answer 10

VPL nucleus

Question 11

What are cutaneous mechanoreceptors and thermal receptors innervated by?

Answer 11

Adelta sensory fibers: may respond to distortion or intense stimuli that is damaging to the skin

Question 12

What are polymodal mechanoreceptors and thermal receptors innervated by?

Answer 12

C type sensory fibers: respond to noxious heat, chemical irritants applied to the skin and sunburn inflammation

Question 13

What is the principal receptor for pain?

Answer 13

naked nerve endings int he epidermis

Question 14

What are the receptors for thermal sensations ?

Answer 14

End bulbs of Krause

Question 15

What is the main receptor for touch, pressure and kinesthesia?

Answer 15

Ruffini’s corpuscle

Question 16

What are the primary neurons in the direct spinothalamic pathway? what is their course?

Answer 16

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

Question 17

Where is the substantia gelatinosa located?

Answer 17

at the tip of the dorsal horn of all lvls of the spinal cord

Question 18

When does the LSTT become the spinal lemniscus?

Answer 18

in the medulla where its joins with VSTT and spinotectal tract

Question 19

describe congenital absence of C type fibers

Answer 19

allows the nonnociceptive fibers to ‘close’ the gate

disinhibition of SG cells -> insensitivity to pain

Question 20

Describe Herpes Zoster

Answer 20

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

Question 21

What does unilateral lesions of the lateral spinothalamic tract result in?

Answer 21

contralateral loss of pain and temperature sensation 2 sensory dermatomal segments below the lvl of the lesion

Question 22

What is the treatment for intractable pain

Answer 22

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

Question 23

What is syringomyelia?

Answer 23

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

Question 24

What parts of the spinal cord is affected by syringomyelia ?

Answer 24

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

Question 25

What does the destruction of anterior horns result in?

Answer 25

LMN paralysis: flaccid paralysis, atrophy, areflexia and antonia

Question 26

What does the destruction of posterior columns result in?

Answer 26

ipsilateral anesthesia proprioceptive and 2pth tactile sensations below the lvl of lesion

Question 27

What does the destruction of the lateral corticospinal tracts result in?

Answer 27

spastic paralysis, hyperrreflexia, hypertonia of the lower extremity

Question 28

What procedure causes a pt to be indifferent to, but very much aware of pain?

Answer 28

prefrontal lobotomy

pain perception also influenced by psychological and sociocultural biases expressed through limbic lobe and neocortex