Sensory

Question 1

Differentiate the different nerve fiber types based on fiber diameter, conduction velocity and function

Answer 1

A-alpha and A-beta - 5-20 u in diameter- 30-70 m/s- touch, pressure

A-gamma- 3-6 u- 15-30 m/s- spindle afferents

A-delta- 2-5 u- 12-30 m/s- pain and temperature, soma touch (sharp, lancinating, pricking pain)

B- 1-3 u- 3-15 m/s

C- 0.3-1.1 u- 0.5 -2 m/s- slow pain and temperature (dull, burning, poorly localized pain)

Question 2

Where do A-delta and C fibers terminate in the dorsal horn?

Answer 2

A-delta in Lamina I mostly, but also in lamina II and lateral part of Lamina V
C- Lamina II

Question 3

What tracts convey pain sensation?

Answer 3

Spinothalamic tract
Spinoreticulothalamic tract/ paleospinothalamic tract
pathway to reticular via short interneurons
direct spinohypothalamic pathway

Question 4

Where do the tracts conveying pain sensation terminate in the thalamus?

Answer 4

Spinothalamic has 2 separate bundles, the lateral division goes to the ventrobasala and posterior group, including the VPL, the medial division goes to the intralaminar complex

Spinoreticulothalamic goes to the medial intralaminar (primarily parafasicular and centrolateral) thalamic nuclei

Question 5

Where do the thalamocortical projections of pain fibers project to?

Answer 5

Ventrobasal and ventroposterior project to the primary sensory cortex and to the upper bank of the sylvian fissure

the Intralaminar nuclei project to the limbic cortex, hypothalamus and the amygdaloid nuclei

Question 6

Give at least 2 examples of descending pain modulation systems

Answer 6

(1) frontal cortex and hypothalamus –> periaqueductal gray –> ventromedial medulla –> dorsal part of lateral fasciculus –> posterior horn (lamina I, II, V)
(2) several other descending pathways, noradrenergic, and serotonergic arise in the locus ceruleus, dorsal raphe nucleus, nucleus reticularis gigantocellularis and are also important modifier of the nociceptive respose

Question 7

What are sclerotomes?

Answer 7

Region of projection of pain that originate in the bones and adjacent ligamentous structures

Question 8

What is causalgia?

Answer 8

Rare type of peripheral neurolgia caused by trauma, with partial interruption of the median, ulnar, sciatic or peroneal nerves. Characterized by persistent, severe pain in the affected limb, more pronounced in the digits, palm or sole. Pain has a burning quality and radiates beyond the territory of the injured nerve. Painful part is exquisitely sensitive to contact. There are sudomotor, vasomotor and later trophic changes that accompany the pain.