Physiology of Pain

Question 1

What is the definition of pain?

Answer 1

an unpleasant sensory and emotional experience, associated with or resembling that associated with actual/potential tissue damage

Question 2

What type of experience is pain?

Answer 2

a conscious experience, arising from integrated sensory and emotional centres in the brain

Question 3

What is nociception?

Answer 3

the neural process of encoding noxious stimuli

Question 4

What is the main difference between pain and nociception?

Answer 4

pain is a conscious experience, nociception does not require consciousness

Question 5

What is a nociceptor?

Answer 5

a neuron that responds specifically to noxious stimuli, which could be mechanical, thermal or chemical

Question 6

Describe the structure of a nociceptor

Answer 6

these are afferent, pseudounipolar neurones
they have shorter proximal axons that terminate in the spinal cord, and longer distal axons that project to skin/other organs

Question 7

What types of nerve fibres are involved in pain transmission?

Answer 7

A delta fibres
C-fibres

Question 8

What type of pain is transmitted by A delta fibres?

Answer 8

fast, sharp pain such as that felt immediately after injury
‘first pain’

Question 9

What type of pain is transmitted by C fibres?

Answer 9

slow, gradual onset pain
‘second pain’

Question 10

Where are cell bodies of sensory nerves located?

Answer 10

just outside the spinal cord, in dorsal root ganglion

Question 11

Where, specifically, does the proximal axon of nociceptors project to?

Answer 11

lamina I and II of the dorsal horn of the spinal cord

Question 12

Describe the structure of A delta fibres

Answer 12

these are thinly myelinated

Question 13

Describe the structure of C-fibres

Answer 13

these are unmyelinated, with a smaller diameter

Question 14

What is the pain pathway from nociceptor to sensory cortex?

Answer 14

1. nociceptor terminates at dorsal horn
2. output from dorsal horn to spinothalamic tract
3. second order neuron follows spinothalamic tract up to the thalamus in the brain
4. third order neuron travels from thalamus to somatosensory cortex

Question 15

List the areas of the brain involved in processing pain

Answer 15

thalamus and somatosensory cortex are responsible for the physical sensation

limbic structures e.g., the anterior cingulate and insular cortex are responsible for the emotional sensation