Pain Gate/Descending Inhibition

Question 1

What is pain gate?

Answer 1

By stimulating the mechanoreceptors (alpha-beta), the inhibitory neurones become excited and block the nociceptors (C fibres) from sending a pain signal to the brain. This closes the pain gate. This creates a decreased response from the dorsal horn.

Mechanoreceptors are larger fibres and travel faster (due to being myelinated).

Question 2

Descending Inhibition (vPAG/dPAG)

Answer 2

• Stimulation of A-Delta fibres causes the release of encephalin (pain relief opioid) in the interneurones of the posterior horn of the spinal cord and the mid-brain.
• Encephalin binds with the delta-receptors and inhibits the C-fibre system, reducing the activation of noxious sensory pathways.