Case 2 - Modulation of the Perception of Pain Flashcards
what is the gate control theory of pain
is a mechanism, in the spinal cord, in which pain signals can be sent up to the brain to be processed to accentuate the possible perceived pain, or attenuate it at the spinal cord itself
what is the gate
the mechanism where pain signals can be let though or restricted
what happens if the gate is open
pain signals can pass through and will be sent to the pain or perceive the pain
what happens if the gate is closed
pain signals will be restricted from travelling up to the brain and the sensation of pain won’t be perceived.
diagram showing the gate control theory of pain
where is the pain gate mechanism located
in the dorsal horn of the spinal cord, specifically in the substantia gelatinousa
what are the interneurones
the interneurones within the substantia gelatinosa are what synapse to the primary afferent neurones, and are where the gate mechanism occurs.
what does the substantia gelatinosa do
modulates the sensory information that is coming in from the primary afferent neurones
what are the three different types of primary afferent neurones
- A-beta fibres
- A-delta fibres
- C fibres
describe A-beta fibres
large diameter fibres, have quick transmission of impulses, due to their myelination - these type of fibres are activated by non-noxious stimuli, such as light, touch, pressure and hair movement
describe A-delta fibres
a smaller diameter fibre - they are thinly myelinated and are stimulated by noxious stimuli, such as pain and temperature, specially sharp, intense tingling sensation
descrie C fibres
have the slowest transmission of impulse since they are not my elated. these type of fibres are activated by pain and temperature, namely prolonged burning sensations
what happens if the interneurones in the SG are stimulated by the non-noxious A beta fibres
an inhibitory response is produced and there are no pain signals sent to the brain, and in this instance the ‘pain gate’ is closed.
what happens if the interneurones are stimulated by the smalller diameter A delta or C fibres
an excitatory response is produced. in this case, pain signals are sent to the brain, these can be modulated, sent back down through descending modulation and perceived as varying amounts of pain
what can the activation of the large diameter A beta fibres do
can help reduce and inhibit the transmission of the small diameter A delta and C fibres
what happens at the spinal cord
the primary afferent neurones come from the periphery and synapse with the second order neurones
where does this happen?
the dorsal horn of the spinal cord
what are the possible neurotransmitter or neuropeptides that can be released
- glutamate
- glycine and GABA
- substance P
- endorphins and serotonin
what happens when glutamate is released
it is excitatory. the activation of the NMDA receptors by glutamate increase receptive field size, decreases activation threshold and extends depolarisation which leads to activation of the dorsal horn neurones
what happens when glycine and GABA are released
they are inhibitory. Glycine can bind onto NMDA, while GABA has its own specific receptors
what happens when substance P is released
it is an excitatory neuropeptide. these are found in respond to tissue damage by causing vasodilation, inflammation or pain
where is substance p found
C fibres
where do endorphins and serotonin get released
into the descending pathway to also help with gate control and the modulation of pain
what are the two types of second order neurones
- wide dynamic range (WDR)
- nociceptive specific range neurones (NS)
where do the WDR neurones synapse tp
the A beta, A delta and C fibres
what are WDR neurones activated by
noxious and non noxious stimuli
where do the NS neurones synapse to
a delta and C fibres
what are the NS neurones activated by
noxious stimuli only
describe the third order neurones
they are located in the brain stem and diacephalon, they transmit the pain signal to the cerebral cortex, where the pain signal, from the a delta or c fibres can be further modulated.
mechanism of action of the TENS
- activates the pain gate mechanism to inhibit pain signals going up to the brain, thus reducing the sensation of pain.
- activates non-noxious afferent fibres, which in turn activates the ‘pain-inhibiting’ interneurones in the spina cord, and thus minimises perceived pain as an output
why does this happen?
because TENS can activate a beta fibres, which helps facilitate the gate control mechanism. the activation of the a beta fibres will inhibit the input from the noxious a delta and c fibres
what does the interferential current (IFC) modality do
inhibits pain through the gate control mechanism, and other neural mechanisms
