Cfibres

Cfibres are unmyelinated nerve fibers in the peripheral nervous system that convey sensory information, especially dull, persistent pain and temperature changes. They are small-diameter fibers (~0.2–1.5 μm) with slow conduction velocities (~0.5–2 m/s). Distinct from myelinated A-delta fibers that mediate sharp, immediate pain, Cfibres sustain signaling after initial injury.

Morphology and subtypes: Cfibres include peptidergic and non-peptidergic populations. They express receptors such as TRPV1 and TRPA1, and release neuropeptides like substance P and calcitonin gene-related peptide (CGRP). They can be polymodal, responding to thermal, chemical (bradykinin, prostaglandins), and sometimes mechanical stimuli. Some Cfibres are cold-sensitive or itch-sensing (pruriceptors).

Physiological role: Their central projections terminate primarily in the superficial dorsal horn (lamina I and II) of the spinal cord, transmitting signals via glutamate and often co-released peptides. They contribute to slow, diffuse pain and to inflammatory and neuropathic pain states through peripheral sensitization and central sensitization (wind-up).

Clinical significance: Alterations in Cfibres are linked to chronic pain conditions and altered pain threshold. They are common targets for analgesic research, including modulators of TRP channels, neuropeptide signaling, and pathways that modulate nociceptor sensitization.