L10 Nociception

Question 1

1. Which of these structures is NOT involved with nociception in dermatomes above spinal cord level T6?
2. primary afferent terminations in the substantia gelatinosa
3. neurons of the dorsal root ganglia
4. primary afferent terminations in the spinal nucleus of trigeminal
5. primary afferent terminates in the cuneate nucleus

Answer 1

Correct: (4) primary afferent terminates in the cuneate nucleus.

The cuneate nucleus is involved with mechanosensation above T6, not nociception.

The DRG neurons and SG terminations are both part of the primary afferent neurons, which relay nociceptive info for the entire body, including dermatomes above T6.

Nerve terminals in the spinal nucleus of trigeminal receive nociceptive info from dermatomes in the head, also above T6.

Question 2

2. Which of these statements regarding nociceptors is always TRUE?
3. they express TRPV1 ion channels
4. they are polymodal
5. they are slowly adapting
6. they respond to capsaicin

Answer 2

Correct: (3) they are slowly adapting

All nociceptors are slowly adapting, such that a continuously applied painful stimulus maintains a continuous firing of action potentials along the afferent fibre. Rapidly adapting receptors are not suitable as nociceptors, as they would stop firing and fail to alert an organism to the potential for tissue damage.

Only heat-sensitive nociceptors express TRPV1 and respond to capsaicin, therefore “a” and “d” are only true in heat-sensitive nociceptors.

Although many nociceptors are polymodal, only some respond to selective stimuli, thus “b” is not always true.