C fibers are a class of unmyelinated nerve fibers responsible for transmitting sensory information related to pain, temperature, and itch. They play a crucial role in the body's sensory system.
Characteristics of C Fibers
- Unmyelinated: Unlike A and B nerve fibers, C fibers lack a myelin sheath. This absence of myelination results in slower conduction velocities.
- Small Diameter: C fibers have a small diameter, further contributing to their slow conduction speed.
- Sensory Function: They primarily transmit sensory information related to:
- Temperature: Detecting changes in temperature, especially noxious heat.
- Pain: Mediating dull, aching, or burning pain (slow pain).
- Itch: Transmitting the sensation of itch.
- Location: C fibers are found throughout the body, including the skin, muscles, and internal organs.
- Synaptic Connections: They terminate primarily in laminae I and II of the dorsal horn of the spinal cord, where they synapse with other neurons to relay sensory information to the brain.
Role in Pain Perception
C fibers are particularly important in the perception of slow, chronic pain. When tissue damage occurs, C fibers are activated by various chemicals released from the damaged cells. This activation leads to the transmission of pain signals to the spinal cord and brain, resulting in the sensation of dull, burning pain that can persist for an extended period. This contrasts with A-delta fibers, which transmit sharp, acute pain more rapidly.
Role in Temperature Sensation
C fibers also contribute to temperature sensation, primarily detecting changes in temperature that are considered noxious or potentially harmful. For example, they are involved in the sensation of burning heat.
Role in Itch Sensation
A specific subset of C fibers is dedicated to transmitting the sensation of itch. These fibers are activated by various pruritogens (itch-inducing substances) and play a critical role in the itch reflex.
Conduction Velocity
Due to the absence of myelination and their small diameter, C fibers have a very slow conduction velocity, typically ranging from 0.5 to 2 meters per second. This slow conduction speed is why the pain signals they transmit are perceived as dull and lingering, compared to the sharp, immediate pain transmitted by faster-conducting A-delta fibers.
