pain

Question 1

what is the specificity theory of pain?

Answer 1

pain is a distinct sensation, detected and transmitted by specific receptors and pathways to distinct ‘pain areas’ of the brain

Question 2

what is the convergence theory of pain?

Answer 2

pain is an integrated, plastic state represented by a pattern of convergent somatosensory activity within a distributed network

Question 3

types of nocicpetors

Answer 3

lightly myelinated A fibres- fast:
- mechano-sensitive
- mechanothermal-sensitive

unmyelinated C fibres - slow:
- polymodal: mechanical, thermal and chemical

Question 4

what are nociceptors?

Answer 4

receptors that response specifically to pain and are a subset of afferents with free nerve endings

Question 5

what are the categories of pain mediated by different fibre types?

Answer 5

fast pain - sharp and immediate, mimicked by direct stimulation of A fibre nociceptors
slow pain - delayed and longer-lasting, mimicked by stimulation of C fibre nociceptors

Question 6

what can activate specific molecular pain receptors?

Answer 6

specific molecular receptors are activated by heat and chillis
the capsaicin receptor (TRPV1) is activated in A and C fibres at 45C and by capsaicin (found in chillis)

Question 7

what are the central pain pathways carrying nociceptive info to the brain?

Answer 7

sensory discriminative: signals location, intensity and type of stimulus
affective-motivational: signals ‘unpleasantness’, enables autonomic activation (fight or flight)

Question 8

what does the discriminative pathway involve?

Answer 8

involves the spinothalamic tract

Question 9

what regions of the brain are activated by pain?

Answer 9

somatosensory cortex (same as non-painful mechanical stimulation)
insula and cingulate cortex (connected to limbic system)

Question 10

features of affective-motivational pathways

Answer 10

• no topographic mapping
• input to limbic (emotional) and hypothalamic (homeostatic) systems
• correlation of unpleasantness of pain with activity of cingulate cortex

Question 11

points to support specificity theory

Answer 11

• cellular and molecular receptors that respond specifically to pain
• specific pathways that convey pain messages
• regions of CNS that are specifically and distinctly activated in response to pain

Question 12

what points don’t fit with specificity theory?

Answer 12

• pain perceived not proportional to intensity of stimulus
• perception of pain in severed limbs (phantom limbs)
• referred pain e.g. viscera to skin
• placebo effect can cure pain
• modulation of pain

Question 13

define hyperalgesia

Answer 13

increased response to painful stimulus

e.g. hypersensitivity of damaged skin to normally tolerable painful stimulus

Question 14

define allodynia

Answer 14

painful response to normally innocuous stimulus

e.g. painful sensitivity of sunburnt skin to light brushing

Question 15

how does hyperalgesia occur?

Answer 15

result of lowered nociceptor thresholds which heightens pain response

1. tissue damage releases ‘soup’ of inflammatory substances
2. prostaglandins lower threshold for axon potential generation

Question 16

what is referred pain?

Answer 16

pain due to damage in the viscera is often perceived as coming from specific locations in skin

Question 17

what does modulation of pain demonstrate?

Answer 17

perception of pain varies according to its context
so mechanisms exist, voluntary of involuntary to overcome pain (also shown by placebo effect)