Lecture 12- Pain

Question 1

Which 2 fibres are connected to Nociceptors peripherally?

Answer 1

Aδ (delta) myelinated axons
C fiber unmyelinated axons

Question 2

describe the differences between Aδ and C fiber axons

Answer 2

Aδ are myelinated, hence have a much faster signal transduction rate (20 m/s), whereas C fibers are unmyelinated with much slower signals (2 m/s).
They are associated with different temporal components of pain, with Aδ causing ‘first pain’- the sharp sudden pain on onset, and C fibres causing the slower, longer lasting pain after this

Question 3

Describe what is seen during subcutaneous electrophysiological recordings of receptors when subject has a lamp of increasing heat above them

Answer 3

the nonociceptive thermoreceptor, begins firing to enable to detection of heat, which then plateaus around the point where the temperature becomes painful (around 45 Celsius), at this point nociceptors start firing at an increasing rate as heat increases

Question 4

Why is eating chilli’s perceived as hot?

Answer 4

Capsaicin is a compound found in chillis which when eaten binds to nociceptors in mouth called vanilloid receptors (these include VR1 and TRPV1) and are found at the end of both Aδ and C fibers. These receptors are ion channels permeable to calcium and sodium, which open from heat and acidity. As they are nociceptors, the heat/pain travels up the spinothalamic tract hence is perceived as pain in the somatosensory cortex/pain complex of brain

Question 5

Is the capsaicin receptor intra- or extracellular?

Answer 5

intracellular- capsaicin is lipid-soluble

Question 6

How is lateral spinal cord damage experienced/tested for?

Answer 6

typically, pain and temperature sensation is lost contralaterally (as it decussates on spinal cord entry) and touch sensation is lost ipsilaterally as it decussates at medullary level

Question 7

define visceral pain

Answer 7

pain originating from internal organs

Question 8

describe referred pain

Answer 8

we don’t have pain/somatosensation travelling directly from internal organ to brain, hence pain sensation is referred and present as pain in other part of body e.g. heart- left chest and arm

Question 9

how can visceral pain be reduced/eliminated in end of life care

Answer 9

lesion the dorsal column at the level of internal organ

Question 10

define affective-motivational pain pathways

Answer 10

pathways additional to those which go to somatosensory cortex, travelling to other regions making up the pain complex, which have affective/motivation aspects

Question 11

draw a diagram of the anterolateral system and what it effects

Answer 11

find image in lecture 12

Question 12

describe how the affective-motivational system indicates top-down modulation

Answer 12

pain has subjective variation in its experience with research showing that despite subjects showing the same thalamic activation, the activation in other brain regions in the pain complex such as the insular and cingulate cortex varies and effects experience reporting
there’s also links between the expectation of pain and how pain is experienced- there is crossover in pain expectation and experience activation with subject expecting higher levels of pain experiencing high levels of pain and vice versa
activation of affective-motivational regions also associated with seeing others in pain - showing activation without the stimuli of pain present

Question 13

describe phantom limb pain

Answer 13

pain in a limb/body part that has been removed, perhaps due to sensitised pain systems in somatosensory cortex/ affective-motivational pain complex

Question 14

describe inhibitory pain neurons

Answer 14

these can reduce the activity of nociceptors (Aδ and C fibres) and can be activated by drugs such as opioids and psychological factors (top-down)