Descending analglesia circuit Flashcards
What is the Descending Analgesia Circuit?
A neural pathway that modulates pain perception, inhibiting pain signals from reaching the brain.
Where does the Descending Analgesia Pathway originate?
In the Periaqueductal Gray (PAG) of the midbrain.
What is the role of the Periaqueductal Gray (PAG) in pain modulation?
It receives signals from higher brain areas (e.g., cortex, amygdala).
It activates the raphe nuclei to inhibit pain transmission.
What neurotransmitter does the PAG use to activate the Raphe Nuclei?
Enkephalins (endogenous opioids).
What is the function of the Raphe Nuclei in the descending pain pathway?
They release serotonin (5-HT) onto the spinal cord.
Serotonin activates inhibitory interneurons in the dorsal horn.
How do inhibitory interneurons reduce pain transmission?
They release endorphins and enkephalins, which inhibit substance P release from primary afferent neurons.
What role does Substance P play in pain signaling?
It is a neuropeptide that transmits pain signals from the periphery to the spinal cord.
How do opioids (e.g., morphine) reduce pain?
They mimic endogenous opioids (endorphins, enkephalins).
They inhibit pain transmission in the spinal cord and brainstem.
What effect does chronic opioid use have on the descending analgesia system?
Leads to tolerance (reduced opioid receptor sensitivity).
Can cause opioid-induced hyperalgesia (increased pain sensitivity).
What are the main neurotransmitters involved in the descending analgesia circuit?
Enkephalins & Endorphins (PAG → Raphe Nuclei)
Serotonin (5-HT) (Raphe Nuclei → Dorsal Horn)
GABA (inhibitory interneurons)
What is the effect of stress-induced analgesia on the descending pain pathway?
Stress activates the PAG, leading to opioid-mediated pain inhibition.
This is why pain perception is reduced in high-stress situations (e.g., during battle or emergencies).
What happens when the descending analgesia pathway is impaired?
Increased pain sensitivity (hyperalgesia).
Reduced effectiveness of opioids.
Possible contribution to chronic pain conditions.
