pain

Question 1

specificity theory

Answer 1

pain is a distinct sensation, detected and transmitted by specific receptors and pathways to distinct “pain areas” of the brain.
SUPPORT :
-There are receptors that respond specifically to pain - A & C fibres
-specific pathways that convey pain messages
-There are regions of the CNS that are specifically and distinctly activated in response to pain
AGAINST:
-Pain perceived is not always proportional to intensity of stimulus
-Modulation by other stimuli (e.g. acupuncture)
-Perception of pain in severed limbs (phantom limbs)
-Referral of pain from viscera to skin
-Placebo effect

Question 2

convergence theory

Answer 2

pain is an integrated, plastic state represented by a pattern of convergent somatosensory activity within a distributed network (a so-called ‘neuromatrix’).

Question 3

A delta fibres

Answer 3

Lightly myelinated A fibres, FAST* ~20m/s
sharp and immediate pain
Mechano-sensitive
Mechanothermal-sensitive

but still slower than proprioceptors

Question 4

C fibres

Answer 4

Unmyelinated C fibres, SLOW ~2m/s
more delayed yet longer lasting pain
Polymodal: mechanical, thermal and chemical

Question 5

free nerve endings

Answer 5

widespread in epithelia and connective tissues

Modality: Pain, heat, cold

Question 6

capsaicin receptor : what is it

Answer 6

it is a TRP: Transient Receptor Potential proteins activated in nociceptive Adelta and C fibres at 45°C when eating chillies

Question 7

Hyperalgesia

Answer 7

Hyperalgesia: result of lowered nociceptor thresholds which heightens pain response.

• tissue damage releases a ‘soup’ of inflammatory substances which affect nerve function, recruit mast cells and neutrophils, and increase local blood flow.
• Prostaglandins lower the threshold for axon potential generation.

Question 8

allodynia:

Answer 8

normally innocuous stimuli (e.g. gentle brushing of the skin) can be perceived as painful

Question 9

Hyperpathia

Answer 9

when there is fibre/axonalloss that results in a raising of the detection threshold
you need a greater level of stimulation before the stimulus is detected
when the detection threshold is exceeded, the subsequent excitability is much greater and patients report ‘explosive’ pain.