GSA Nociception

Question 1

fundamental concept of GSA nociception

Answer 1

Pain stimuli travel via local reflex paths and relay paths to higher centers in both systems

Question 2

Spinothalamic tract reflex arcs

Answer 2

• monosynaptic: direct synapse of sensory fiber with motor neuron
• polysynaptic: interneurons in the reflex arc (pain stimuli -> LMN -> UMN)

Question 3

spinothalamic tract for relay to higher centers (classic pathways in primates)

Answer 3

1st Neuron = Dorsal root ganglion
-axons ascend or descend a few segments forming the dorsolateral fasiculus (aka Lissauer’s Tract)
2nd Neuron = dorsal gray horn of spinal cord
-axons immediately cross and ascend contralaterally in the ventrolateral funiculus as spinothalamic tract
3rd Neuron = ventral caudal lateral (VCL) neuron of the thalamus
-axons contribute to formation of internal capsule, ascend to appropriate part of cerebral cortex

Question 4

Spinothalamic tract relay differences in animals

Answer 4

bilateral, diffuse, many synapses possible

Question 5

Quintothalamic tract cranial reflex arc

Answer 5

1st Neuron = trigeminal ganglion
-axons ascend and descend a short distance forming the spinal tract of the trigeminal nerve
2nd Neuron = location depends on modality of sensation (pontine sensory nucleus for mechanical sensations, spinal nucleus of the trigeminal nerve for thermal stimuli)
-axon synapses in brainstem on motor nuclei of appropriate cranial nerves
3rd neuron = any motor neuron of appropriate cranial nerve
-axons leave brainstem through a cranial nerve to reach peripheral target

Question 6

Quintothalamic tract for relay to higher centers

Answer 6

1st neuron = Trigeminal ganglion
-axons ascend and descend a short distance forming the spinal tract trigeminal nerve
2nd neuron = location depends on modality of sensation (pontine sensory nucleus for mechanical sensation, spinal nucleus of trigeminal nerve for thermal sensations)
-axons immediately cross to the opposite side and ascend contralaterally as trigeminal lemniscus
3rd neuron = ventral caudal medial nucleus of the thalamus
-axons contribute to the formation of the internal capsule and synapse in the appropriate part of the cerebral cortex

Question 7

Divisions of GSA nociception are

Answer 7

Spinothalamic tract = Spinal Nerves - carry info from the body
Quintothalamic tract = Cranial Nerves - carry info from head