Pain And Temperature Pathways

Question 1

Burning pain and deep, dull, aching, diffuse pain are conveyed via which pathway?

Answer 1

Diffuse indirect spinothalamic system ("slow" pain) pathway
Paleospinothalamic system (polyneuronal, polysynaptic divergent)
Primary fibers are unmyelinated, type C fibers

Question 2

Describe the indirect spinothalamic pathway (“slow” pain)

Answer 2

Primary fibers are unmyelinated C fibers with slow conduction rate
Upon entering spinal cord, they bifurcate and ascend and descend in dorsolateral fasciculus of Lissaur
Some fibers terminate in nucleus proprius, while others terminate in substantia gelatniosa and ascend in direct spinothalamic system
Secondary axons from nucleus proprius course in fasciculus proprius and terminate on interneurons
Some fibers from nucleus proprius may ascend to thalamus as spinoreticular fibers that are part of fasciculus proprius.
These terminate in midline reticular formation of brainstem, hypothalmus, and centromedian nucleus of dorsal thalamus

Question 3

The fasciculus prorpius is part of a diffuse neuronal net called ___

Answer 3

Reticular formation

This surrounds gray matter of spinal cord and extends rostrally through core of brainstem to thalamus

Question 4

What occurs if there is a unilateral lesion of the spinoreticular fibers?

Answer 4

No significant sensory deficits

Indirect spino-reticulo-thalamic pathway is too bilateral and diffuse to be affected by unilateral lesions

Question 5

Describe the direct spinothalamic pathway (“fast” pain)

Answer 5

Pain receptors
Primary neurons in the spinal ganglia send central processes into spinal cord
Secondary neurons in the substantia gelatinosa send axons through the anterior white commissure to form the lateral spinothalamic tract (LSTT) (and go through spinal lemniscus)
Tertiary neurons in the VPL nucleus of dorsal thalamus send axons to the postcentral gyrus which is the primary somesthetic cortex

Question 6

Describe the primary neurons in the direct spinothalamic pathway

Answer 6

Cell bodies are located in spinal ganglia
Axons of Adelta and C type fibers enter spinal cord through lateral division of dorsal root and bifurcate to ascend and descend (+/- 2 segments) in dorsolateral fasciculus.
Adelta terminates on secondary neurons in substantia gelatinosa
C type fibers terminate in nucleus proprius

Question 7

Describe secondary neurons in substantia gelatinosa

Answer 7

Axons cross anterior white commissure and ascend in contralateral anterolateral funiculus as the lateral spinothalamic tract (LSTT)
Sacral levels enter first and in posterolateral aspect
Cervical levels enter tract last and in anteromedial aspect

Question 8

In the medulla, the LSTT joins the VSTT and spinotectal tract to form ___

Answer 8

Spinal lemniscus (SL)
This terminates in ventral posterior lateral (VPL) nucleus of dorsal thalamus

Question 9

Describe tertiary neurons in VPL nucleus of thalamus

Answer 9

VPL nucleus receives sensory information from contralateral one-half of body via spinal lemniscus
Tertiary axons leave VPL as thalamic radiations which course through posterior limb of internal capsule and corona radiata to finally terminate in primary somesthetic cortex (postcentral gyrus)

Question 10

Where do all conscious sensory pathways project to?

Answer 10

Primary somesthetic cortex (postcentral gyrus) in a somatotopic arrangement
Information entering originated from opposite side of body

Question 11

Sharp, pricking, highly-localized pain is conveyed via which pathway?

Answer 11

Direct spinothalamic ("fast" pain) pathway
Part of neospinothalamic system
Peripheral processes of primary neurons have Adelta fibers which have thin myelin