Neuroanatomy of the brachial plexus: the missing link in the continuity between the central and peripheral nervous systems.

The brachial plexus is a complex network of nerves which extends from the neck to the axilla and which supplies motor, sensory, and sympathetic fibers to the upper extremity. Generally it is formed by the union of the ventral primary rami of the spinal nerves, C5-C8 and T1, the so-called "roots" of the brachial plexus. The goal here is to examine the neural architecture of the brachial plexus. The most constant arrangement of nerve fibers will be delineated, and then the predominant variations in neural architecture will be defined, particularly the prefixed and postfixed plexus, as well as the microanatomy and anatomy of the major terminal branches of the plexus. Multiple tracts connect many parts of the nervous system, and multiple ascending and descending tracts connect the peripheral nervous system (PNS) and lower spinal centers with the brain. This reflects that the nervous system is able to extract different pieces of sensory information from its surroundings and encode them separately, and that it is able to control specific aspects of motor behavior using different sets of neurons. Examination of the major sensory or motor pathways reveals a highly and tightly organized nervous system. In particular, at each of many levels, we see fairly exact maps of the world within the brain. In an effort to understand the functional neuroanatomy of the brachial plexus, this paper will focus briefly on the nervous connections of the nerves of the upper extremity with the brain. The goal here is to better understand "what the brain sees" after nerve injury and repair.