Which fibre type’s pain is not blocked by opioids?

Which fibre type’s pain is not blocked by opioids?

• A. A-beta fibers.
• B. C fibers.
• C. A-gamma fibers.
• D. A-delta fibers.

Answer: (D)

Opioids work by activating mu receptors in the spinal cord to inhibit the release of excitatory neurotransmitters from nociceptive nerve endings, with a stronger effect on the slow, dull pain carried by C fibers. Fast, sharp pain, which is transmitted by the myelinated A-delta fibers, relies on rapid signal transmission and tends to be less susceptible to this opioid-mediated inhibition. Because of this, pain from A-delta fibers is not blocked as effectively by opioids as pain from C fibers. A-beta fibers carry non-nociceptive touch signals, which are not the target of opioid analgesia for nociceptive pain. So the fast, sharp pain associated with A-delta fibers is the type that opioids block less effectively.

Opioids work by activating mu receptors in the spinal cord to inhibit the release of excitatory neurotransmitters from nociceptive nerve endings, with a stronger effect on the slow, dull pain carried by C fibers. Fast, sharp pain, which is transmitted by the myelinated A-delta fibers, relies on rapid signal transmission and tends to be less susceptible to this opioid-mediated inhibition. Because of this, pain from A-delta fibers is not blocked as effectively by opioids as pain from C fibers. A-beta fibers carry non-nociceptive touch signals, which are not the target of opioid analgesia for nociceptive pain. So the fast, sharp pain associated with A-delta fibers is the type that opioids block less effectively.