Nociception Flashcards
(45 cards)
Adelta fibre diameter:
1-5um.
Adelta fibre CV:
3-30m/s.
C fibre diameter:
0.2-1.5um.
C fibre CV:
0.5-2m/s.
Abeta fibre diameter:
6-12um.
Abeta fibre CV:
33-75 m/s.
Membrane of nociceptors contain receptors that …
Covert energy of noxious stimuli into depolarising electrical potential.
What ion channel mediates pain producing action of capsaicin, and is activated by temperatures over 45C?
TRPV1.
What is the menthol-responsive and cold-sensing channel?
TRPM8.
What does congenital pain insensitivity show about the role of other ion channels (v-g sodium channels) in nociception?
Caused by loss of function mutation in SCN9A gene encoding NaV1.7 v-g Na+ channel.
Mutations in SCN9A gene can also cause what? Implicated in what condition?
Hyperexcitability of nociceptors. Inherited erythromelalgia, ongoing burning pain of extremities.
Role of v-g Na+ channels also highlighted by what pharmacological evidence?
Local anaesthetics, lidocaine, blocks v-g Na+ in primary afferent fibre.
What mechanism highlights the role of inflammation in pain sensitivity?
TRPv1-mediated membrane currents are enhanced by a reduction in pH, characteristic of the chemical milieu of inflammation.
Describe the spinothalamic tract:
Sensory neurons synapse in dorsal root ganglion, second order neurons decussate and ascend in anterolateral white matter to the VPL. Then somatosensory cortex.
Describe the spinoreticular tract:
Fibres decussate after DRG and ascend the contralateral cord to reach the brainstem reticular formation, before projecting to the thalamus and hypothalamus.
Describe the spinomesencephallic tract:
DRG, decussate, travel upwards in anterolateral column to midbrain, terminating in PAG and superior colliculus.
Role of the spinothalamic tract:
Localisation.
Role of the spinoreticular tract:
Arousal and emotional responses to pain.
Role of the spinomesencephalic tract:
Modulates pain by connections with the PAG.
What evidence is there that the VPL organises input from the spinothalamic tract according to body region, preserving spatial fidelity of signal to somatosensory areas?
Neurons in VPL have small RFs matching those of presynaptic spinal neurons .
What evidence is there that the thalamus plays a role in pain?
Electrical stimulation of thalamus leads to intense pain. And lesions can cause neuropathic pain condition Dejerine-Roussy syndrome. Causes spontaneous burning pain and abnormal sensations (dysesthesias).
Gate control theory suggests that pain arises from the …
Balance of activity in nociceptive and non-nociceptive afferent fibres.
What is the mechanism behind gate control theory?
Activation of non-n neurons engages inhibitory interneurons in the dorsal horn, closing a gate for the transmission of afferent signals. Activation of n neurons opens the gate.
Evidence for gate control theory?
Activation of low threshold afferent fibres can attenuate pain, TENS machine. Electrodes at peripheral locations can activate large diameter fibres innervating areas that overlap and surround area of pain.
