Lecture 23: Pain

Question 1

What is pain?

Answer 1

an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage

Question 2

What are the sensory-discriminative aspects of pain?

Answer 2

location, intensity and duration

Question 3

What is the motivational-affective dimension of pain?

Answer 3

unpleasant feeling associated with pain

Question 4

What does pain evoke?

Answer 4

emotional as well as sensory experiences

Question 5

What is nociception?

Answer 5

the neural process of encoding noxious stimuli

activation of cells throughout the entire nervous system

Question 6

What are nociceptors?

Answer 6

cells that are physiologically activated by noxious stimuli

Question 7

What is nociceptive pain?

Answer 7

pain that arises from actual or threatened damage to non-neural tissue and is due to the activation of nociceptors

Question 8

How is nociceptive pain signalled to the brain?

Answer 8

different noxious stimuli can activate specific receptors and/or ion channels on peripheral nociceptors

Question 9

What is inflammatory pain?

Answer 9

pain that is driven by inflammation

Question 10

How is inflammatory pain signalled to the brain?

Answer 10

some inflammatory mediators directly activate peripheral nociceptors to produce pain
others produce changes in sensitivity of peripheral nociceptors to noxious stimuli

Question 11

What is neuropathic pain?

Answer 11

pain caused by a lesion or disease of the somatosensory nervous system
changes in circuit sensitivity and CNS connections

Question 12

What is the role of nociceptors?

Answer 12

transduce noxious stimuli into electrical potentials and take information to the CNS

Question 13

How is pain signalled to the brain (in general)?

Answer 13

ascending pathways transmit information towards cerebrum -> pain perception occurs in cerebrum -> descending modulation of pain signalling can suppress pain

Question 14

What do peripheral nociceptors respond to and what do they code for?

Answer 14

usually respond to high threshold stimulation

code for intensity of noxious stimulation

Question 15

How fast do peripheral nociceptors conduct action potentials?

Answer 15

conduct slowly relative to low threshold sensory neurons

Question 16

What is the structure of peripheral nociceptors?

Answer 16

usually described as having un-specialised, free nerve endings

Question 17

How can peripheral nociceptors be classified?

Answer 17

according to the conduction properties of their axons

Question 18

What are the two types of peripheral nociceptors?

Answer 18

Aδ-fibre axons and C-fibre

Question 19

What are the properties of Aδ-fibre axons?

Answer 19

thinly myelinated
conduction velocities 5-30 m/s
fast (sharp) pain

Question 20

What are the properties of C-fibre axons?

Answer 20

unmyelinated
conduction velocities <2 m/s
slow (burning) pain

Question 21

What do mechanical nociceptors respond to?

Answer 21

noxious mechanical stimuli, eg. cutting, crushing, pinching

Question 22

What do thermal nociceptors respond to?

Answer 22

noxious temperature

Question 23

What do polymodal nociceptors respond to?

Answer 23

combinations of mechanical/thermal, and/or chemicals or inflammatory
mediators

Question 24

What does the dorsal horn of the spinal cord receive input from? Where do second order neurons originate?

Answer 24

nociceptors

in different lamina and ascend toward the brain

Question 25

What is the role of interneurons in the dorsal horn of the spinal cord?

Answer 25

communicate between lamina and contribute to processing

Question 26

What is the main ascending pathway for discriminative aspects of pain / temperature for the body?

Answer 26

anterolateral system / spinothalamic tract -> ventral posterior lateral nucleus of the thalamus -> primary somatic sensory cortex

Question 27

What will a lesion in the spinal cord lead to?

Answer 27

reduced sensation of two-point discrimination on the ipsilateral side and reduced sensation of temperature and pain on the contralateral side

Question 28

How can pain be modulated at different levels of the neuraxis?

Answer 28

sensitisation, neurogenic inflammation, descending inhibition and common analgesics

Question 29

What is sensitisation?

Answer 29

increased responsiveness of nociceptive neurons to their normal (noxious) input, and/or recruitment of a response to normally subthreshold (innocuous) inputs

Question 30

What is hyperalgesia?

Answer 30

increased pain from a stimulus that normally provokes pain

Question 31

What is allodynia?

Answer 31

pain due to a stimulus that does not normally provoke pain

e.g. sunburn causes pain to normally innocuous touch

Question 32

What is peripheral sensitisation?

Answer 32

increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields

Question 33

What is central sensitisation?

Answer 33

increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input

Question 34

What is neurogenic inflammation?

Answer 34

when peripheral nociceptors release inflammatory mediators that produce or exaggerate local tissue inflammation

Question 35

What is NGF?

Answer 35

an inflammatory mediator which sensitizes bone nociceptors and produces sensitivity to weight bearing

Question 36

What is the role of descending systems in regards to pain?

Answer 36

can modulate the transmission of ascending pain signals e.g. inhibition of pain signal as it passes through the dorsal horn / pain can be shut down by higher centres

Question 37

What are common analgesics?

Answer 37

paracetamol, opioids, NSAIDs and local anaesthetics