Case 2 - Modulation of the Perception of Pain

Question 1

what is the gate control theory of pain

Answer 1

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

Question 2

what is the gate

Answer 2

the mechanism where pain signals can be let though or restricted

Question 3

what happens if the gate is open

Answer 3

pain signals can pass through and will be sent to the pain or perceive the pain

Question 4

what happens if the gate is closed

Answer 4

pain signals will be restricted from travelling up to the brain and the sensation of pain won’t be perceived.

Question 5

diagram showing the gate control theory of pain

Answer 5

Question 6

where is the pain gate mechanism located

Answer 6

in the dorsal horn of the spinal cord, specifically in the substantia gelatinousa

Question 7

what are the interneurones

Answer 7

the interneurones within the substantia gelatinosa are what synapse to the primary afferent neurones, and are where the gate mechanism occurs.

Question 8

what does the substantia gelatinosa do

Answer 8

modulates the sensory information that is coming in from the primary afferent neurones

Question 9

what are the three different types of primary afferent neurones

Answer 9

• A-beta fibres
• A-delta fibres
• C fibres

Question 10

describe A-beta fibres

Answer 10

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

Question 11

describe A-delta fibres

Answer 11

a smaller diameter fibre - they are thinly myelinated and are stimulated by noxious stimuli, such as pain and temperature, specially sharp, intense tingling sensation

Question 12

descrie C fibres

Answer 12

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

Question 13

what happens if the interneurones in the SG are stimulated by the non-noxious A beta fibres

Answer 13

an inhibitory response is produced and there are no pain signals sent to the brain, and in this instance the ‘pain gate’ is closed.

Question 14

what happens if the interneurones are stimulated by the smalller diameter A delta or C fibres

Answer 14

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

Question 15

what can the activation of the large diameter A beta fibres do

Answer 15

can help reduce and inhibit the transmission of the small diameter A delta and C fibres

Question 16

what happens at the spinal cord

Answer 16

the primary afferent neurones come from the periphery and synapse with the second order neurones

Question 17

where does this happen?

Answer 17

the dorsal horn of the spinal cord

Question 18

what are the possible neurotransmitter or neuropeptides that can be released

Answer 18

• glutamate
• glycine and GABA
• substance P
• endorphins and serotonin

Question 19

what happens when glutamate is released

Answer 19

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

Question 20

what happens when glycine and GABA are released

Answer 20

they are inhibitory. Glycine can bind onto NMDA, while GABA has its own specific receptors

Question 21

what happens when substance P is released

Answer 21

it is an excitatory neuropeptide. these are found in respond to tissue damage by causing vasodilation, inflammation or pain

Question 22

where is substance p found

Answer 22

C fibres

Question 23

where do endorphins and serotonin get released

Answer 23

into the descending pathway to also help with gate control and the modulation of pain

Question 24

what are the two types of second order neurones

Answer 24

• wide dynamic range (WDR)
• nociceptive specific range neurones (NS)

Question 25

where do the WDR neurones synapse tp

Answer 25

the A beta, A delta and C fibres

Question 26

what are WDR neurones activated by

Answer 26

noxious and non noxious stimuli

Question 27

where do the NS neurones synapse to

Answer 27

a delta and C fibres

Question 28

what are the NS neurones activated by

Answer 28

noxious stimuli only

Question 29

describe the third order neurones

Answer 29

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.

Question 30

mechanism of action of the TENS

Answer 30

• 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

Question 31

why does this happen?

Answer 31

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

Question 32

what does the interferential current (IFC) modality do

Answer 32

inhibits pain through the gate control mechanism, and other neural mechanisms