Spinal Circuits for Touch, Pain, and Itch

Question 1

What are mechanoreceptors?

Answer 1

Sensory nerve endings depolarised by mechanical force of skin

Question 2

What are the 5 types of mechanoreceptors?

Answer 2

Merkel cells
Meissner corpuscles
Pacinian corpuscles
Ruffini endings
Free nerve endings

Question 3

What do Merkel cells detect and are they superficial/deep?

Answer 3

Light pressure

Superficial

Question 4

What do Meissner corpuscles detect and are they superficial/deep?

Answer 4

Light vibration

Superficial

Question 5

What do Pacinian corpuscles detect and are they superficial/deep?

Answer 5

Strong vibration

Deep

Question 6

What do Ruffini endings detect and are they superficial/deep?

Answer 6

Stretch

Deep

Question 7

What do free nerve endings detect?

Answer 7

Nociception (nociceptors)

Itch (pruritoceptors)

Question 8

What do low-threshold MS transduction molecule-expressing neurons detect?

Answer 8

Innocuous mechanical

Question 9

What do TRPA1 transduction molecule-expressing neurons detect?

Answer 9

Nociception, pruritoception

Question 10

What do TRPV1 transduction molecule-expressing neurons detect?

Answer 10

Nociception, pruritoception, capsaicin

Question 11

What do TRPV3 transduction molecule-expressing neurons detect?

Answer 11

Warm

Question 12

What do TRPM8 molecule-expressing neurons detect?

Answer 12

Cold, menthol

Question 13

What are the characteristics of Abeta fibres and what do they detect?

Answer 13

Thick myelination
Fast conduction
Innocuous touch

Question 14

What are the characteristics of Adelta fibres and what do they detect?

Answer 14

Thin myelination
Slow conduction
Sharp pinprick pain

Question 15

What are the characteristics of C fibres and what do they detect?

Answer 15

Unmyelinated
Very slow conduction
Long-lasting burning pain

Question 16

What do Ia and Ib afferents detect?

Answer 16

Proprioception

Question 17

From superficial to deep, in which order do the sensory afferents terminate in the spinal cord?

Answer 17

C fibres
A fibres
Ia and Ib afferents

Question 18

How does injury/stimulation affect dorsal spinal cord neuron receptive fields?

Answer 18

Changes size

Question 19

Which laminae do projection neurons to brain originate from?

Answer 19

I and IV/V

Question 20

Name the 4 methods of sensory afferent input processing by dorsal horn circuitry

Answer 20

Spatial convergence
Modality convergence
Selective amplification
Selective inhibition

Question 21

Name the 3 theories of interneuron central processing

Answer 21

Intensity theory
Specificity theory
Combinatorial code theory

Question 22

Describe intensity theory

Answer 22

Convergence of multiple afferents onto interneuron
Need certain intensity of any stimulus to interpret
If 2 modalities input to same interneuron simultaneously highest intensity modality perceived

Question 23

Describe specificity theory

Answer 23

One afferent synapses onto interneuron with corresponding modality

Question 24

Describe combinatorial coding theory

Answer 24

One afferent synapses onto interneuron with corresponding modality
Afferent also activates other afferents and their interneurons
Interaction and opponency between pathways carrying signals
Sensation depends on combined activation of pathways

Question 25

What does Melzack and Wall’s gate theory of pain suggest?

Answer 25

Touch input allows inhibition of pain transmission

Convergence of 2 modalities