Brachial Plexus

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  • Topic: Brachial plexus, Nerves of the upper limb, Median nerve
  • Pages : 9 (2823 words )
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  • Published : October 30, 2012
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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. -------------------------------------------------

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. -------------------------------------------------

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 shoulder joint and provides motor innervation to the supraspinatus and infraspinatus muscles. The ventral ramus of C7 continues as the middle trunk. The ventral rami of C8 and T1 unite to form the lower trunk. -------------------------------------------------

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Divisions
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Each trunk splits into an anterior division and a posterior division. These separate the innervation of the ventral and dorsal aspect of the upper limb. The anterior divisions usually supply flexor muscles. The posterior divisions usually supply extensor muscles. -------------------------------------------------

Cords
The cords are referred to as the lateral, posterior, and medial cord, according to their relationship with the axillary artery. The cords pass over the first rib close to the dome of the lung and continue under the clavicle immediately posterior to the subclavian artery. The anterior divisions of the upper and middle trunks unite to form the lateral cord, which is the origin of the lateral pectoral nerve (C5, C6, C7). The anterior division of the lower trunk forms the medial cord, which gives off the medial pectoral nerve (C8, T1), the medial brachial cutaneous nerve (T1), and the medial antebrachial cutaneous nerve (C8, T1). The posterior divisions from each of the 3 trunks unite to form the posterior cord. The upper and lower subscapular nerves (C7, C8 and C5, C6, respectively) leave the posterior cord and descend behind the axillary artery to supply the subscapularis and teres major muscles. The thoracodorsal nerve to the latissimus dorsi (also known as the middle subscapular nerve, C6, C7, C8) also arises from the posterior cord. -------------------------------------------------

Musculocutaneous nerve branch
The musculocutaneous nerve is a mixed nerve containing sensory and motor axons. It is derived from the lateral cord. The...
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