What action does a local anesthetic have on unmyelinated C fibers?

Local anesthetics primarily block nerve conduction in unmyelinated C fibers, which are responsible for transmitting pain and temperature sensations. When a local anesthetic is applied, it inhibits the depolarization of these nerve fibers, preventing the generation and propagation of action potentials. This blockade effectively diminishes or completely interrupts the transmission of pain and temperature signals from the peripheral tissues to the central nervous system.

This mechanism is particularly important in clinical practice, where local anesthetics are used to manage pain during and after surgical procedures. The selective action of local anesthetics on C fibers allows for targeted pain relief without significantly affecting other sensory modalities that are carried by myelinated fiber pathways.