Physiology of Pain

Question 1

What does the IASP define pain as?

Answer 1

An unpleasant sensory and emotional experience, associated with active tissue damage or described in terms of such damage

Question 2

What are the four processes in the physiology of pain?

Answer 2

Transduction, transmission, modulation, perception

Question 3

What is transduction of pain?

Answer 3

Translation of noxious stimulus into electrical activity at the peripheral nociceptor

Question 4

What is transmission of pain?

Answer 4

Propagation of pain signal as nerve impulses through the nervous system

Question 5

What is pain modulation?

Answer 5

Modification/hindering of pain transmission in the nervous system (e.g by inhibiting neurotransmitters like endogenous opioids)

Question 6

What is perception of pain?

Answer 6

Conscious experience of pain, causes physiological and behavioural responses

Question 7

What does pain begin with?

Answer 7

The activation of nociceptors

Question 8

What are nociceptors?

Answer 8

Specific primary sensory afferent neurons normally activated by intense noxious stimuli

Question 9

What does the central terminal release?

Answer 9

Neurotransmitters that excise second order neurons

Question 10

What does depolarisation caused by noxious stimuli elicits?

Answer 10

Action potentials that propagate to the CNS

Question 11

What kind of neurons are nociceptors?

Answer 11

First order neurons that relay information to second order neurons in the CNS by chemical synaptic transmission

Question 12

Where do second order neurons ascend?

Answer 12

The spinal cord in the anterolateral system to terminate in the thalamus

Question 13

What makes up the anterolateral tract of the spinal cord?

Answer 13

The spinothalamic tract (STT) and the spinoreticular tract (SRT)

Question 14

What is the spinothalamic tract involved in?

Answer 14

Pain perception (location, intensity)

Question 15

What is the spinoreticular tract involved in?

Answer 15

Autonomic responses to pain arousal, emotional responses and fear of pain

Question 16

Where is sensory information relayed from the thalamus?

Answer 16

To the primary sensory cortex (by third order neurons)

Question 17

What kind of tissue do nociceptors innervate, and what activates them?

Answer 17

Innervate peripheral tissues; activated only be mechanical, thermal or chemical stimuli that are noxious

Question 18

What are A-delta fibres?

Answer 18

Mechanical/thermal nociceptors that are thinly myelinated (conduction velocity 6-30m/s), respond to noxious mechanical/thermal stimuli, mediate “first” pain

Question 19

What are C-fibres?

Answer 19

Unmyelinated nociceptors (conduction velocity 0.5-2 m/s), collectively respond to all noxious stimuli (are polymodal), mediate “second” pain

Question 20

What are some ways to classify pain?

Answer 20

Mechanisms = nociceptive, inflammatory, pathological
Time course = acute, chronic, breakthrough pain
Severity = mild, moderate, severe
Source of origin = somatic, visceral

Question 21

What does nociceptive pain represent?

Answer 21

Normal response to injury of tissues by noxious stimuli

Question 22

What is the only way nociceptive pin can be provoked?

Answer 22

By intense stimulation of nociceptors by noxious stimuli

Question 23

What is the function of nociceptive pain?

Answer 23

Adaptive = functions as early warning physiological protective system to detect and avoid noxious stimuli

Question 24

What activates inflammatory pain?

Answer 24

The immune system by tissue injury or infection

Question 25

What releases mediators at the site of inflammation to cause inflammatory pain?

Answer 25

Leucocytes, vascular endothelium, tissue resident mast cells (causes hyperalgesia and allodynia)

Question 26

What is hyperalgesia?

Answer 26

Heightened pain sensitivity to noxious stimuli

Question 27

What is allodynia?

Answer 27

Pain sensitivity to innocuous stimuli

Question 28

How is inflammatory pain adaptive?

Answer 28

It promotes repair until healing occurs by discouraging physical contact with the affected part and also discourages movement

Question 29

What are the two categories of pathological pain?

Answer 29

Neuropathic and dysfunctional

Question 30

What cause neuropathic pain?

Answer 30

Damage to neural tissue = compression neuropathies, peripheral neuropathies, central pain (following stroke), postherpetic neuralgia, trigeminal neuralgia, phantom limb

Question 31

How can neurological pain be perceived?

Answer 31

Burning, shooting, numbness, pins and needles, may be less localised

Question 32

What are some features of dysfunctional pain?

Answer 32

No identifiable damage or inflammation, is maladaptive

Question 33

What are some examples of dysfunctional pain?

Answer 33

Fibromyalgia, IBS, tension headache, TMJ disease, interstitial cystitis

Question 34

How can dysfunctional pain be treated?

Answer 34

Simple analgesics not effective, sometimes treated with drugs not originally mean for pain (antidepressants or anti-epileptics)

Question 35

What is referred pain?

Answer 35

Pain developed in one part of the body felt in another structure away from the place of its development

Question 36

What kind of pain is usually referred?

Answer 36

Deep or visceral pain (pain from superficial structures isn’t normally referred)

Question 37

What causes referred pain?

Answer 37

Convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level