2.05 Pain and thermosensation Flashcards
What are nociceptors activated by?
Intense stimuli -therma -mechanical -chemical that are nocious/damaging
Where is the cell body located for nociceptors?
Dorsal root ganglia and trigeminal ganglia
Are all A-delta and c-fibres nociceptors?
No, but all nociceptors are A-delta or C-fibres.
Which nociceptors mediate first/fast pain?
A-delta fibres.
Thinly myelinated.
mechanical/thermal nociceptors- respond to mechnical and thermal stimuli
Which nociceptors mediate second/slow pain?
C-fibres
unmyelinated
respond to all noxious stimuli.
How is intensity of a nociceptive stimulus enoded in the nervous system?
More intense stimuli produce higher frequency nociceptor activation.
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
C-MH
c-fibre, mechnical, and heat (and chemical heat)
Which c-fibre is described:
responds to noxious mechanical stimuli only
C-M
c-fibre, mechanical
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
C-H
c-fibre that normally only responds to heat, can be sensitised
Which c-fibre is described?
normally insensitive to mechanical and heat stimuli
acquire sensitivity with inflammation
sensitive to capsaicin and other algesic substances
C-MiHi(silent)
C-fibre, not normally sensitive to mechanical or heat stimuli
What distinguishes A-MH type 1 from type 2?
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 ***
Where do nociceptive C and a-delta fibres terminate?
Which cells do they synapse with?
Typically laminae 1 and 2 (superficial)
They synapse with nociceptive specific cells
What kind of sensation modality is input from A-beta fibres?
proprioceptive
What range of sensation modality do wide dynamic range neurons recieve input from?
all three types of fibres
- a-delta
- a-beta
- c
What are the main neurochemicals in the synapse between the first and second order pain sensory neurons? (dorsal horn of spinal cord)
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)
What neurotransmitters do the interneurons release?
GABA
Glycine
Opiates
cannabinoids
All of these suppress transmission
What is the mechanism for referred pain?
Visceral and skin afferents converge on some of the same spinothalamic neurons.
The brain interprets the visceral information as occurring in the body wall.
Pain from the right neck region may be referred from _____.
Liver
Pain from the right shoulder tip may be referred from _____.
Gallbladder
Pain from the left jaw, left chest, and down the inside of the left arm may be referred from _____.
The heart
Pain from the left shoulder(possible right shoulder) may be referred from ______.
The diaphragm/lungs
Pain from the xiphisternum may be referred from —–?
stomach, pancreas
Pain from the umbilical region may be referred from —-?
appendix.
In which tracts do the nociceptive signal ascend the spinal cord in?
mainly the anterolateral system:
- spinothalamic tract
- spinoreticular tract
What modality does the spinoreticular tract mostly transmit?
slow c-fibre pain
connects with reticular nuclei: periaqueductal grey, parabrachial nucleus
Which nociceptive tract is responsible for the autonomic responses to pain, arousal, emotional responses, and fear of pain?
Spinoreticular tract.
This is due to its connections with reticular nuclei.
Where do Spinothalamic tract projection neurons originating from lamina 1 (fast fibre a-delta pain) terminate in?
Posterior nucleus of the thalamus
Where do spinothalamic tract projection neurons originating from lamina V (wide dynamic range) terminate in?
posterior and ventroposterior nucleus of the thalamus
True or false: all sensory afferents are excitatory?
True.
This is why the gate control theory was revised, to exlude a first neurone that is inhibitory in the sensory circuit
True or false: we can sense differences in temperature as small as 0.01 degree c
True
Which transient receptor potential (TRP) channels are implicated in thermosensation? TRPA1 TRPV1 TRPV2 TRPV4 TRPM8
TRPV 1
TRPV3
TRPV4
TRPM8
substances such as chlli, camphor, and mint are implicated.
