Pain Physiology

Question 1

Define pain.

Answer 1

An unpleasant sensory and emotional experience associated with actual or potential damage.

Question 2

According to the psychology of pain, list and elaborate on the dimensions of pain.

Answer 2

1. Sensory discriminative - sense of intensity, location , quality and duration of pain
2. Motivational affective - how you feel about the pain (unpleasantness and urge to escape), involving limbic system
3. Cognitive evaluation - how the pain affects the thought process and personality

Question 3

What are the different ways of classifying pain?

Answer 3

Fast pain vs slow pain
- fast = conducted by A delta fibers, small myelinated fibres
- slow = conducted by C fibres, thin unmyelinated fibres

OR

Physiological vs pathological pain
- good/acute pain = sudden onset and is receded during the healing process
- chronic/bad pain = caused by nerve injury which may be due to toxins, ischaemia or diabetes

Question 4

What receptors are responsible for pain transduction?

Answer 4

Painful stimuli are perceived through a mutlimodal receptor molecule found on pain fibres known as the vallinoid receptor (TVRP1)

Question 5

Describe how the transduction of pain which occurs upon eating chilli peppers.

Answer 5

Chilli peppers contain an extract called capsaicin which gives them their spiciness. It activates the calcium and sodium ligand gated changed by binding to the VR1 receptor.
This then results in the influx of Calcium and sodium into nociceptor, which then brings about an action potential which is propagated to the CNS.

Heat and acid also bring about opening of the channels.

Pathway involved in the spinothalamic tracts (lateral)

Question 6

How many of the laminate of Rexed in the spinal cord are attributed to receiving pain?

Answer 6

The first 6

Question 7

What are the effects of spinal lesions on pain?

Answer 7

Pain is transmitted via the spinothalamic pathway.
Affected on the contralateral side (beneath the lesion)

Question 8

Define allodynia.

Answer 8

Pain due to a stimulus that does not normally provoke pain.

Question 9

Define the term hyperalgesia.

Answer 9

Increased pain from a stimulus that normally provokes pain

Question 10

Define the term hypoalgesia

Answer 10

Diminished pain in response to a normally painful stimulus

Question 11

What is the definition of peripheral sensitisation? And under which circumstances does this occur?

Answer 11

The reduced threshold and augmented response of the sensory nerve fibres in the peripheral to external stimulus

Occurs in presence of tissue damage, inflammation, sympathetic terminals

Question 12

What is referred pain?

Answer 12

It is pain perceived at a location other than the site of the painful stimulus or origin

Question 13

What are the two endogenous systems for pain management? Expand of these.

Answer 13

1. The gate theory
   - unmodulated pain travels via C fibers from nociceptors and synapses onto the secondary order neurons, sending strong signals to the thalamus
   - modulated pain includes the actions from an inhibitory interneuron and dorsal columns from the skin mechanoreceptors
   - dorsal column has excitatory effects (traveling via A delta fibres) on inhibitory neuron and therefore making C fibers stop perceiving the pain for a moment
2. Descending pain inhibition pathways

Question 14

What are the exogenous substances used for pain management?

Answer 14

1. Inhibitions of perceptions (opioid, anaesthetics)
2. Inhibition of transmission - impulse conduction (local anaesthetics, alpha 2 agonists)
3. Modulation of spinal pathways - inhibit central sensitization (NSAIDS, opioids, anticonvulsants)
4. Inhibit transduction - peripheral sensitisation of nociceptors (NSAIDS, opioids, corticosteroids, local anaesthetics)