Pain physiology

Question 1

What is pain?

Answer 1

Unpleasant sensory + emotional experience to actual or potential tissue damage
Conscious experience

Question 2

What is somatosensation?

Answer 2

Physiological process resulting in perception of pain, pressure + touch

Question 3

What is nociception ?

Answer 3

Physiological response to actual or potential tissue damage

Noxious stimuli ( actual/potential tissue damage) are detected by nociceptors and a signal is generated in the periphery 
Sensory afferents transmit info to the dorsal horn of the spinal cord

Question 4

What are the 4 main processes of pain

Answer 4

Transduction: Noxious stimuli detected by nociceptors, nociceptors convert into an electrical impulse
Transmission: Electrical impulse is relayed up the spinal cord
Modulation: Factors can change pain transmission along the pathway in periphery/spinal/supraspinal
Perception: Signal relayed to cingulate, limbic and sensory cortex

Question 5

What do nociceptors release?

What do these substances do?

Answer 5

Pro inflammatory mediators
They allow for nociception
Activate macrophages + mast cells to release more pro inflammatory molecules to exaggerate and relay the noxious stimuli

Question 6

What are the 3 main afferent fibres?

What do they synapse with and wear?

Answer 6

A delta - fast rapid “sharp pain thinly myelinated, fast conduction
C fibres - ouch “second pain”, no myelination
A beta - heavily myelinated, light touch + pressure

A beta synapse with 2nd ON in lamina III-V

Question 7

What type of cell does the DRG contain?

Answer 7

Glial cells -> induce signal transmission + store signals ( chronic pain)

Question 8

What are the 2 main types of 2nd ON?

Answer 8

Wide dynamic neurones : Receive input from A delta, C + A beta fibres. Respond to noxious + non noxious stimuli
Nociceptive sensitive neurones: Only receive input from noxious stimuli

Question 9

Describe the axon reflex

Answer 9

Noxious stimulus activate the spinal cord and local axonal branches
Collateral axon branches have changes in blood flow and immune activation.

Question 10

Describe the inflammatory soup

Answer 10

• Facilitates transduction + transmission
• Nociceptors detect tissue damage + release inflammatory mediators to stimulate mast cell + macrophages
• Release more pro inflammatory substances
• This reinforces process and generates electrical impulse
• Release of pro inflammatory substances by mast cell provides positive feedback to the vasomotor system
  catecholamines + psotanoids released
  NT ( substance P + cgpr) allow for AP production + electrical impulse transmission