physiology of pain 1

Question 1

What is pain

Answer 1

An unpleasant sensory experience associated with tissue damage, accompanied with an emotional reaction.

Question 2

Why do we feel pain

Answer 2

It is a warning sign so we can avoid harmful situations, prevents injury or death and tells us to rest following injury,

Question 3

How is pain classified

Answer 3

Nociceptive- normal functioning of nociceptors in response to tissue injury
neuropathic- pain in response to an injury to the ns

Question 4

What are nociceptors

Answer 4

they are primary sensory neurons that detect pain, they are pseudo unipolar neurons.

Question 5

How are sensory nerve fibre s classified?

Answer 5

They are classified by diameter and myelin content
largest; A-alpha and A-beta fibres, myelinated with large diameter and receptive to light touch and proprioception

slightly smaller A-delta fibres- thinly myelinated, medium diameter, light touch, temp and nociception

c fibres- unmyelinated, small diameter, temp and nociception.

Question 6

Outline the stimuli that can activate nociceptors

Answer 6

pressure, heat, cold, chemical, tissue damage and inflammation.

Question 7

outline the polymodal nociceptors

Answer 7

most c fibre nociceptors are polymodal, they respond to pressure, temp and chemical.

Question 8

Outline temp transduction

Answer 8

Involves TRP channels which can have chemical agonists e.g. TRPV1 detects hot temp but also agonistic to capsaicin.
TRPM detects cold and is a menthol agonist
TRPA1 detects V cold and cinnamon

Question 9

Name chemicals that can directly activate nociceptors

Answer 9

ATP, Protons and seretonin

Question 10

What effect does inflammation have on nociceptors

Answer 10

inflammation can modulate nociceptors and cause hypersensitivity

Question 11

What are some important terms?

Answer 11

hyperalgesia: noxious stimuli produce an exaggerated pain response
allodynia: non-noxious stimuli produce a painful response

Question 12

What are the 2 main mechanisms that lead to hypersensitivity

Answer 12

peripheral sensitization which leads to hyperalgesia

central sensitization leads to allodynia (secondary hyperalgesia)

Question 13

outline peripheral sensitization

Answer 13

peripheral sensitization is an increase in the responsiveness of the peripheral ends of nociceptors
driven by tissue injury or inflammation.

an example of this is sunburn and then taking a warm shower which will burn more than it should

Question 14

Outline the action of bradykinin

Answer 14

bradykinin indirectly acts on TRPV1,

bradykinin binds to the receptor, activation of protein kinase which leads to the phosphorylation of TRPV1

Question 15

What is the spinothalamic tract

Answer 15

pain information ascends the spinothalamic tract

the central axon passes through the dorsal root to reach the dorsal horn and then forms collateral branches and form the tract of Lissauer

on the tip of the dorsal horn, they synapse into second-order neurons in the substantial gelatinosa.

Question 16

Outline the second-order neurons

Answer 16

the axon of the second-order neurons cross the midline of the spinal cord and those axons enter the anterolateral column and ascend to the thalamus where they synapse onto 3rd order neurons.

Question 17

Outline referred pain

Answer 17

the convergence of visceral and cutaneous nociceptors on same second-order neurons in the spinal cord.

the brain perceives visceral pain as cutaneous.

Question 18

Where do third-order neurons project to

Answer 18

They ascend to the primary somatosensory cortex,

Question 19

Outline the emotional component of pain

Answer 19

Third-order pain also projects to the insula, cingulate cortex and limbic system which are all involved in encoding the emotional part of the pain.

Question 20

What are the 2 important regions in the descending regulation of pain and how is pain inhibited

Answer 20

The periaqueductal grey matter and rostral ventromedial medulla. PAG grey matter neurons excite serotonergic neurons which excite inhibitory interneurons.

inhibitory interneurons inhibit spinothalamic tract neurons.