Brachial Plexus

The brachial plexus is a somatic nerve plexus formed by intercommunications among the ventral rami (roots) of the lower 4 cervical nerves (C5-C8) and the first thoracic nerve (T1). It lies partly in the neck and partly in the axilla. It is responsible for the motor innervation of all of the muscles of the upper extremity, with the exception of the trapezius and levator scapula. The brachial plexus supplies all of the cutaneous innervation of the upper limb, except for the area of the axilla (which is supplied by the supraclavicular nerve) and the dorsal scapula area, which is supplied by cutaneous branches of the dorsal rami.
The brachial plexus is subdivided into roots, trunks, divisions, cords, and branches. Typically, the brachial plexus is composed of 5 roots, 3 trunks, 6 divisions, 3 cords, and terminal branches.
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Roots
The ventral rami of spinal nerves C5 to T1 are referred to as the "roots" of the plexus. The roots emerge from the transverse processes of the cervical vertebrae immediately posterior to the vertebral artery, which travels in a cephalocaudad direction through the transverse foramina. Each transverse process consists of a posterior and anterior tubercle, which meet laterally to form a costotransverse bar. The transverse foramen lies medial to the costotransverse bar and between the posterior and anterior tubercles. The spinal nerves that form the brachial plexus run in an inferior and anterior direction within the sulci formed by these structures.
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Trunks
Shortly after emerging from the intervertebral foramina, the 5 roots (C5-T1) unite to form 3 trunks. The trunks of the brachial plexus pass between the anterior and middle scalene muscles.
The ventral rami of C5 and C6 unite to form the upper trunk. The suprascapular nerve and the nerve to the subclavius arise from the upper trunk. The suprascapular nerve contributes sensory fibers to the