Pain and Pain Suppression Flashcards
Highly myelinated axons
Convey mechanical pain very quickly and precisely, very informative about location
Unmyelinated axons
Convey different kinds of pain more slowly and less precisely, more vague about location
Types of nociceptors
Sensitive to extremes of mechanical stimulation
Sensitive to pungent irritants (eg mustard oil)
Sensitive to extremes of temperature, acid and capsaicin
Pain Perception
Can be independent of input
Physical pain perception –> Primary SS Cortex
Unpleasantness perception –> Anterior Cingulate Cortex
The Descending Analgesia Circuit reduces pain by…
Inhibiting the pain signal from entering the central nervous system at the first synapse
How could pain be suppressed? (Non-drug)
- Direct stimulation of the PAG (Periacridotal Grey Area) by electrodes - chronic pain sufferers
- Stressful situations - athletes and soldiers
- Placebo effect
- Acupuncture (tested using naloxone, an opiate receptor blocker)
What is Capsaicin?
Used topically on the skin for muscle pain and feels hot.
How does capsaicin work?
Depletes sensory neuron terminals of substance P, providing local analgesia
How do Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) - eg aspirin, ibuprofen and COX-2 inhibitors - work?
Act peripherally - poor blood-brain-barrier penetration because of binding proteins in the blood
Inhibit Cyclo-Oxygenase 1 and 2 (COX-1 and COX-2) which reduce the production of prostaglandins
Side effects of inhibiting COX-1
COX-1 is involved in blood clotting so taking aspirin prevents blood clotting
Also involved in protecting the stomach lining from acid - making NSAIDs bad for the stomach
How does paracetamol work?
Still under investigation but:
1. Paracetamol reacts with endogenous molecules to form AM404, an agonist of the TRPV1 and CB-1 cannabinoid receptors
Where are TRPV1 channels found?
On nociceptors
Where are CB-1 receptors found?
In many central and peripheral pain-related circuits, including Descending Analgesia Circuit where they reduce inhibition
Opiates
Derived from the opium poppy
Long-time used and very powerful analgesics
Well-known for their abuse potential
Different forms of opiates
Opium - mostly smoked or eaten
Morphine - many different ways, only 20% crosses blood-brain barrier
Codeine - typically oral, as cough suppressant
Heroin - typically injected; lipid soluble so more crosses the blood-brain barrier
Oxycodone - pills with either fast (15 minutes on empty stomach) or slow uptake