NEURO 230 Pain

Question 1

What is pain?

Answer 1

Unpleasant sensory and emotional experience associated with potential or actual tissue damage

Question 2

What is nociception?

Answer 2

Sensory process providing signals that provide pain

Question 3

What is congenital insensitivity pain syndrome?

Answer 3

mutation in Na+ channels meaning no pain sensation therefore reducing life expectancy

Question 4

What is chronic pain?

Answer 4

Pain that persists beyond normal healing time 3-6 months

Question 5

What is hyperalgaesia?

Answer 5

increased pain response to a noxious stimuli

Question 6

What is allodynia?

Answer 6

Pain response to a non-noxious stimuli

Question 7

What is parasthesia?

Answer 7

Pain response in absence of any stimulus

Question 8

What are nociceptors and give some examples

Answer 8

Free nerve endings with specific receptors on membrane
e.g Thermal: TRPV1 detects temperature and spicy food (capsaicin)
Chemical - inflammation
Mechanical - excessive stretch

Question 9

What different nociceptive fibres are there?

Answer 9

A-delta, C fibres, A beta fibres and Aalpha fibres

Question 10

Describe A-delta fibres?

Answer 10

Fast pain fibres - they are unimodal, myeliinated fibres so can only detect one type of pain that is not necessarily distinguishable

Question 11

Describe C fibres

Answer 11

Slow pain fibres that are unmyelinated but polymodal and can provide further information about the pain

Question 12

Describe A-beta fibres

Answer 12

detect pressure and tactile sensation and have a slow response - enter spinal cord through same pathway as A-delta and can inhibit them by activating inhibitory interneurones

e.g. rubbing an injury lessens pain

Question 13

What are A-alpha fibres

Answer 13

Myotatic reflex ! fast fibres detecting stretch in the GTO/muscle spindle

Question 14

What is the 1st order neurone in pain pathway?

Answer 14

Nociceptors

Question 15

What is the 2nd order neurone in the pain pathway?

Answer 15

Spinothalamic tract/ Ascending pathways

Question 16

What is the 3rd order neurone in the pain pathway?

Answer 16

The projections from the thalamus to the cortex

Question 17

What is the substantia gelatinosa?

Answer 17

Region of the dorsal horn where nociceptors synapse with interneurones

Question 18

Describe the pain pathway

Answer 18

Stimulus –> nociception –> dorsal horn in spinal cord –> decussation in lateral spinothalamic tract –> ST tract –> thalamus (VPL) –> thalamus –> cortex

Question 19

What is the VPL in the thalamus?

Answer 19

ventro-postero-lateral nucleus

Question 20

Where in the cortex do projections from the thalamus go to in the pain pathway?

Answer 20

Insula/ Cingulate cortex = unpleasant association with pain

1ry somatosensory cortex = location of painful stimuli

Question 21

What are the 3 descending pathways in pain and what is their function?

Answer 21

modulate the ascending pathways
peri-aqueductal grey (opioidergic)
Nucleus raphe magnus ( serotinergic)
Locus coeruleus ( noradrenergic)

Question 22

At the level of the spinal cord how is their descending modulation/downregulation?

Answer 22

Inhibitory interneurones contain enkephalins - they synapse in the spinal cord to both 1st and 2nd order neurones. Act on opioid receptors unhibiting NT release and hyperpolarising the post synaptic membrane

This is activated by descending pathways

Question 23

What are the main opioid receptors?

Answer 23

Mu - addictive

Delta and Kappa

Question 24

What are the types of opioids?

Answer 24

Endorphins (agonist to all groups of receptor)
Enkephalins - delta agonists
Dynorphins - kappa agonists

Question 25

How does inflammation cause pain?

Answer 25

Inflammation sensitises nociceptors by PG's, substance P and bradykinin self-perpetuating as nociceptors also release substance P

Question 26

How do opiates act?

Answer 26

upregulate descending pathways, direct inhibition and blunt emotional responses

Question 27

What is neuropathic pain?

Answer 27

due to neuronal damage = nociceptive stimulation

Question 28

What is trigeminal neuralgia?

Answer 28

Usually due to compression of the trigeminal nerve causing intense episodic pain on stimulation treated with anticonvulsants

Question 29

What is phantom limb pain?

Answer 29

Perception of pain in a limb that is no longer there

Question 30

What is the physiology behind phantom limb pain?

Answer 30

massive loss of nociceptors but the remaining pain perception pathways are there - input may be sensitised. There is reorganisation within the dorsal horn and somatosensory cortex so that pain fibres are activated by crude touch byt the somatosensory cortex confuses it with being in the region lost

Question 31

What is the 1st step on the WHO pain ladder?

Answer 31

non-opioid +/- adjuvant

Question 32

What is the 2nd step on the WHO pain ladder?

Answer 32

weak-opioid + non- opioid +/- adjuvants

Question 33

What is the 3rd step on the WHO pain ladder?

Answer 33

strong -opioid + non opioid +/i adjuvants

Question 34

What pain adjuvant therapies are there?

Answer 34

bisphosphonates, steroids, muscle relaxants and ADM's