Which statement about TRP receptors and pain modalities is true?

• A. Nociceptors are not linked to any receptors
• B. Pain modalities are exclusively chemical and have no receptor specificity
• C. Free nerve endings are not involved in nociception
• D. Certain pain modalities are linked to specific receptors (TRP)

Answer: (D)

Pain signaling depends on TRP receptors on nociceptors, which are ion channels on free nerve endings that respond to different stimuli and convert them into electrical signals. This creates modality-specific pain because each TRP receptor detects particular kinds of stimuli. For example, TRPV1 responds to heat and capsaicin, TRPM8 to cold and menthol, and TRPA1 to various irritants. Because these receptors assign distinct stimuli to specific pathways, certain pain modalities are linked to specific receptors. The other statements are inconsistent with what we know: nociceptors do have receptors; pain modalities are not purely chemical without receptor specificity; and free nerve endings are the site of nociception.