Nerve and Blood Vessels

Abstract

From the histologic point of view, nerves are round or flattened cords, with a complex internal structure made of myelinated and unmyelinated nerve fibers, containing axons and Schwann cells grouped in fascicles (Fig. 4.1a) (Erickson 1997). Along the course of the nerve, fibers can traverse from one fascicle to another and fascicles can split and merge. Based on the fascicular arrangement, two theories have been hypothesized to explain the internal architecture of a nerve: the ``cable'' and the ``plexiform'' models (Stewart 2003). The first states that nerves are cable-like structures, in which fascicles run separately throughout the entire nerve length (Fig. 4.1b). The second asserts that fascicles alternate splitting, branching, and rejoining along the course of the nerve trunk (Fig. 4.1c). In fact, nerves have both cable and plexiform arrangement of the fascicles depending on the level of examination. In their more proximal portion (e.g., brachial plexus), a plexiform organization of the fascicles predominates.