2.05 Pain and thermosensation

Question 1

What are nociceptors activated by?

Answer 1

Intense stimuli
-therma
-mechanical
-chemical 
that are nocious/damaging

Question 2

Where is the cell body located for nociceptors?

Answer 2

Dorsal root ganglia and trigeminal ganglia

Question 3

Are all A-delta and c-fibres nociceptors?

Answer 3

No, but all nociceptors are A-delta or C-fibres.

Question 4

Which nociceptors mediate first/fast pain?

Answer 4

A-delta fibres.
Thinly myelinated.
mechanical/thermal nociceptors- respond to mechnical and thermal stimuli

Question 5

Which nociceptors mediate second/slow pain?

Answer 5

C-fibres
unmyelinated
respond to all noxious stimuli.

Question 6

How is intensity of a nociceptive stimulus enoded in the nervous system?

Answer 6

More intense stimuli produce higher frequency nociceptor activation.

Question 7

Which c-fibre is described:
responds to noxious mechanical stimuli, activated by noxious heat (threshold 39ºC - 51ºC), sensitive to capsaicin. Shows sensitization to repeated stimuli. Contributes to heat pain and location of the stimulus

Answer 7

C-MH

c-fibre, mechnical, and heat (and chemical heat)

Question 8

Which c-fibre is described:

responds to noxious mechanical stimuli only

Answer 8

C-M

c-fibre, mechanical

Question 9

Which c-fibre is described:
responds to noxious heat
normally not responsible to mechnical stimuli
sensitive to capcaisin
responsible for heat hyperalgesia
contributes to precise localization of stimulus

in context of inflammation- sensitive to mechanical stimuli

Answer 9

C-H

c-fibre that normally only responds to heat, can be sensitised

Question 10

Which c-fibre is described?
normally insensitive to mechanical and heat stimuli
acquire sensitivity with inflammation
sensitive to capsaicin and other algesic substances

Answer 10

C-MiHi(silent)

C-fibre, not normally sensitive to mechanical or heat stimuli

Question 11

What distinguishes A-MH type 1 from type 2?

Answer 11

A-MH type 1:

• strong mechanical stimuli needed
• activated my noxious heat
• not sensitive to capsaicin
• sensitized to prolonged stimuli
• threshold drops in tissue injury

A-MH type 2

• noxious mechanical stimuli
• activated by noxious heat
• sensitive to capsaisin***
• shows adaptation
• mediates first pain to heat ***

Question 12

Where do nociceptive C and a-delta fibres terminate?

Which cells do they synapse with?

Answer 12

Typically laminae 1 and 2 (superficial)

They synapse with nociceptive specific cells

Question 13

What kind of sensation modality is input from A-beta fibres?

Answer 13

proprioceptive

Question 14

What range of sensation modality do wide dynamic range neurons recieve input from?

Answer 14

all three types of fibres

• a-delta
• a-beta
• c

Question 15

What are the main neurochemicals in the synapse between the first and second order pain sensory neurons? (dorsal horn of spinal cord)

Answer 15

primary transmiter is GLUTAMATE- EPSP, activating post-synaptic AMPA receptors. mGluRs are also involved
-substance P and CGRP cause slow and prolonged EPSP that relieves voltage dependent Mg2+ block on NMDA receptor (they get activated)

Question 16

What neurotransmitters do the interneurons release?

Answer 16

GABA
Glycine
Opiates
cannabinoids

All of these suppress transmission

Question 17

What is the mechanism for referred pain?

Answer 17

Visceral and skin afferents converge on some of the same spinothalamic neurons.
The brain interprets the visceral information as occurring in the body wall.

Question 18

Pain from the right neck region may be referred from _____.

Answer 18

Liver

Question 19

Pain from the right shoulder tip may be referred from _____.

Answer 19

Gallbladder

Question 20

Pain from the left jaw, left chest, and down the inside of the left arm may be referred from _____.

Answer 20

The heart

Question 21

Pain from the left shoulder(possible right shoulder) may be referred from ______.

Answer 21

The diaphragm/lungs

Question 22

Pain from the xiphisternum may be referred from —–?

Answer 22

stomach, pancreas

Question 23

Pain from the umbilical region may be referred from —-?

Answer 23

appendix.

Question 24

In which tracts do the nociceptive signal ascend the spinal cord in?

Answer 24

mainly the anterolateral system:

1. spinothalamic tract
2. spinoreticular tract

Question 25

What modality does the spinoreticular tract mostly transmit?

Answer 25

slow c-fibre pain

connects with reticular nuclei: periaqueductal grey, parabrachial nucleus

Question 26

Which nociceptive tract is responsible for the autonomic responses to pain, arousal, emotional responses, and fear of pain?

Answer 26

Spinoreticular tract.

This is due to its connections with reticular nuclei.

Question 27

Where do Spinothalamic tract projection neurons originating from lamina 1 (fast fibre a-delta pain) terminate in?

Answer 27

Posterior nucleus of the thalamus

Question 28

Where do spinothalamic tract projection neurons originating from lamina V (wide dynamic range) terminate in?

Answer 28

posterior and ventroposterior nucleus of the thalamus

Question 29

True or false: all sensory afferents are excitatory?

Answer 29

True.

This is why the gate control theory was revised, to exlude a first neurone that is inhibitory in the sensory circuit

Question 30

True or false: we can sense differences in temperature as small as 0.01 degree c

Answer 30

True

Question 31

Which transient receptor potential (TRP) channels are implicated in thermosensation? 
TRPA1
TRPV1
TRPV2
TRPV4 
TRPM8

Answer 31

TRPV 1
TRPV3
TRPV4
TRPM8

substances such as chlli, camphor, and mint are implicated.