What happens in the descending pain pathway with opioids?

• A. Activation of descending neurons that release norepinephrine and serotonin to reduce pain
• B. Activation of ascending neurons that increase pain
• C. No effect on pain signaling
• D. Increases dopamine release in nucleus accumbens

Answer: (A)

Opioids relieve pain by engaging the brain’s descending inhibitory system. When opioids bind mu receptors in regions like the periaqueductal gray, they activate a descending pathway that projects to the nucleus raphe magnus and the locus coeruleus. These centers then release serotonin and norepinephrine in the spinal cord, where they dampen nociceptive transmission at the dorsal horn. This suppression reduces the amount of pain signal that reaches the brain. It’s a spinally mediated analgesic effect driven by NE and 5-HT, not primarily by increasing dopamine in the nucleus accumbens.