Substance P is found in which type of primary afferent nerve fibers?

Substance P is found in which type of primary afferent nerve fibers?

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

Answer: (C)

Substance P is a neuropeptide released by small-diameter, unmyelinated primary afferent neurons that carry nociceptive (pain) signals. These are the C fibers, which convey dull, slow, throbbing pain and contribute to inflammatory pain responses in the dorsal horn and peripheral tissue. Because C fibers are peptidergic and able to release substances like Substance P, this neuropeptide is characteristically found there. In contrast, A-delta fibers are fast, myelinated nociceptors that primarily use glutamate as a transmitter for sharp pain, A-beta fibers carry non-nociceptive touch, and B fibers are autonomic and not involved in somatic pain transmission.

Substance P is a neuropeptide released by small-diameter, unmyelinated primary afferent neurons that carry nociceptive (pain) signals. These are the C fibers, which convey dull, slow, throbbing pain and contribute to inflammatory pain responses in the dorsal horn and peripheral tissue. Because C fibers are peptidergic and able to release substances like Substance P, this neuropeptide is characteristically found there. In contrast, A-delta fibers are fast, myelinated nociceptors that primarily use glutamate as a transmitter for sharp pain, A-beta fibers carry non-nociceptive touch, and B fibers are autonomic and not involved in somatic pain transmission.