Which nerve fiber type is most easily blocked by local anesthetics?

Which nerve fiber type is most easily blocked by local anesthetics?

• A. A fibers
• B. B fibers
• C. C fibers
• D. D fibers

Answer: (B)

Local anesthetics block voltage-gated sodium channels, preventing action potential propagation. The ease of blockade depends on fiber size and myelination: small, myelinated fibers are inhibited most readily. The preganglionic autonomic fibers are among the smallest and are myelinated, so they lose conduction with lower doses of local anesthetic compared to larger or unmyelinated fibers. This is why autonomic (sympathetic) blockade occurs early with regional anesthesia. Among the fiber types listed, those small, myelinated autonomic fibers are the most susceptible to blockade, making them the easiest to block.

Local anesthetics block voltage-gated sodium channels, preventing action potential propagation. The ease of blockade depends on fiber size and myelination: small, myelinated fibers are inhibited most readily. The preganglionic autonomic fibers are among the smallest and are myelinated, so they lose conduction with lower doses of local anesthetic compared to larger or unmyelinated fibers. This is why autonomic (sympathetic) blockade occurs early with regional anesthesia. Among the fiber types listed, those small, myelinated autonomic fibers are the most susceptible to blockade, making them the easiest to block.