Neuroscience review

Question 1

nociceptors (noci is derived from the Latin nocere, “to hurt”), like other somatic sensory receptors, arisin from cell bodies located in the ?

Answer 1

dorsal root ganglia (or the trigeminal ganglion)

Question 2

Are the axons associated with nociceptors fast or slow conducting?

Answer 2

slow conducting

**only lightly myelated **

Question 3

Axons conveying nociception are categorized into two groups

Answer 3

1) A∂ fiber-- mechanosensitive and mehanothermal nociceptors; fast conducting (20m/s); myelated

respond to dangerously intense mechanical or to mechanothermal stiumuli and hae receptife fields that consist of clusters of sensitive spots.

2) C fiber– slow conducting (less than 2m/s); mostly unmyelated

respond to thermal, mechanical, and chemical stimuli (polymodal)

Question 4

first pain vs. second pain

Answer 4

A(alpha) and Aß axons in peripheral nerves don’t produce pain (they are rapidly conducting)

pain stimulus → activate A(delta) → sharp pain → increase stimulus → C fibers recruited → longer lasting dull pain experienced

It is possible to selectively anesthetize C and A(delta) fibers!

Question 5

Name some afferent nociceptice endings and what stimulates them…

Answer 5

all receptors respond to both heat and to capsaicin

vanilloid receptor (A(delta) and C fibers) moderate (45degree) heat and capsaicin

vanilloid-like receptor (VRL-1 or TRPV2) has higher threshold resonse to heat and is NOT senstive to capsaicin

Question 6

dorsolateral tract of Lissauer

Answer 6

nociceptive nerves axons from the dorsal root ganglion enter the spinal chord here, then run up and/or down for one or two spinal chord segments before penetrating the grey matter of the dorsal horn

Question 7

The axons of second-order neurons begin in Rexed’s laminae/dorsal horn of spinal cord and then…

Answer 7

cross to the contralateral side and ascend to the brainstem and thalamus in the anterolateral or ventrolateral side of the spinal cord.

(Note that mechanosensory fibers cross in the caudal medulla–high up!– so a spinal cord lesion can produce ipsilateral mechanosensory deficits and contralateral pain/temp deficits)

Question 8

The mechanosensory pathway ascends ipsilaterally in the cord, so a unilateral spinal lesion will produce sensory loss of touch, pressure, vibration, and proprioception below the lesion on the same side. The pathway for pain and temperature, however…

Answer 8

cross the midline to ascentd on the opposite side of the cord. Thus, diminished sensation of pain below the lesion will be observed on the side opposite the mechanosensory loss (and the lesion).