The mantle fibers are anesthetized first during local anesthesia because they are located on the outer part of the nerve bundle, making them more accessible to the anesthetic agent. These fibers typically innervate proximal structures and are larger in diameter. In contrast, the core fibers, which innervate distal regions, are protected by the mantle fibers and require longer exposure to the anesthetic for effective blockade. Additionally, sympathetic fibers, which are small and unmyelinated or thinly myelinated, are anesthetized early but not before mantle fibers. Motor fibers are generally more resistant and anesthetized last. Understanding this pattern is essential for achieving effective and selective anesthesia in surgical and dental procedures.

Reference: Medical Physiology, Guyton and Hall, 13th Edition.