Regional Anesthesia of the Upper Extremity.

Anatomy of the brachial plexus Roots The brachial plexus is most commonly formed by five roots originating from the ventral divisions of spinal nerves C5 through T1. The roots of the plexus are located in the cervical paravertebral space, between the anterior and middle scalene muscles. Besides understanding its origins, it is also important to understand the plexus in terms of the relative surface area occupied by its components at different levels of its trajectory. As shown in figure 1 each root of the plexus emerges from an intervertebral foramen. The C5 root appears between cervical vertebrae 4 and 5, while the T1 root emerges between thoracic vertebrae 1 and 2.