The brachial plexus part of neck anatomy is a complex region of nerve fibers that run from the spine, proceed through the neck, into the armpit and through the arm. These nerve fibers include the ventral rami of the first thoracic nerve root (T1) and the lower four cervical nerve roots (C5). The nerves in the brachial plexus control the wrist, arm, hand, elbow, and shoulder. Injury to this area is quite common, particularly in those who play contact sports such as wrestling, rugby, football, and hockey. Repeated minor trauma to the area can also cause problems in some individuals, including children, with inflammation causing compression of these nerves. Brachial plexus neuritis or neuropathy is not considered a common disorder and is often confused with other neck problems such as cervical spondylosis (arthritis) and cervical radiculopathy (a pinched nerve in the neck).
Cervical radiculopathy is thought to be the most common cause of pain in the neck and shoulder region, especially when neurological deficits, such as weakness and numbness, also occur. This radiculopathy is due to herniated or bulging disc in neck most often, although osteophyte growth can also be responsible for compression. As brachial plexus neuritis mimics cervical radiculopathy in many respects it is important to differentiate the two, especially as treatment varies greatly for each condition. Viral infection, chemical exposure, and immunologic factors are also associated with brachial plexus neuritis. The severity of the condition, and the extent of damage prior to treatment, has a significant effect on the recovery rate and incidence of permanent disability.
Anatomy of the Brachial Plexus
The brachial plexus has five ‘terminal’ branches and a number of other paths exiting the plexus at different points. These five major roots are the anterior rami of the spinal nerves and merge to create three trunks; the superior (upper C5-C6), the middle (C7), and the inferior (lower C8-T1). Each trunk splits in two, forming six further paths and are classified as anterior or posterior superior, middle, or inferior trunks. These then regroup into three cords and are classified according to their relationship to the axillary artery. The posterior cord (C5-T1) constitutes the posterior of the three trunk divisions, the lateral cord (C5-C7) is formed from the anterior divisions from the upper and middle trunks, and the anterior division of the lower trunk continues to form the medial cord (C8-T1). By understanding the anatomy of the brachial plexus it becomes easier to see how damage and inflammation in the area can cause symptoms such as radicular pain in the arm and shoulder.
The nerves in the brachial plexus are responsible for innervating almost the whole of the upper limb, with cutaneous and muscular functionality. The brachial plexus includes both motor nerves, which carry messages to the muscles from the central nervous system and stimulate movement, and sensory nerves, which carry messages to the brain about pain, pressure, and temperature. The trapezius muscle, which is commonly worked on by physical therapists trying to ameliorate neck, back, and shoulder pain, is innervated instead by the spinal accessory nerve (CN XI). An area of the skin near the armpit is also innervated by a nerve other than those included in the brachial plexus, namely, the intercostobrachial nerve.
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