What type of nerve fibers are most affected by local anesthetics?

Local anesthetics target various types of nerve fibers, but they primarily affect the smaller, unmyelinated nerve fibers more significantly than the larger, myelinated ones. In the context of the given question, all nerve fiber types, including A-delta, B, and C fibers, can be impacted by local anesthetics, but they do so to different extents based on their size and myelination.

A-delta fibers, which are myelinated, transmit sharp pain and temperature sensations. B fibers, which are also myelinated but smaller in diameter, transmit autonomic functions. C fibers, being unmyelinated and smaller than both A-delta and B fibers, are responsible for dull, aching pain and temperature sensations. Local anesthetics disrupt nerve conduction by blocking sodium channels, and because C fibers are the least resistant to blockade due to their small size and lack of myelination, they are significantly affected, often resulting in loss of pain sensation first.

In clinical practice, when local anesthetics are administered, they typically first affect the C fibers, followed by A-delta and B fibers. Consequently, while local anesthetics can affect all of these types of fibers, the multimodal effects on them lead to consistent outcomes