Brachial Plexus Injury


Original Editor ­ Aarti Sareen

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Introduction

Brachial plexus is the network of nerves which runs through the cervical spine, neck,axilla and then into arm or it is a network of nerves passing through the cervico-axillary canal to reach axilla and innervates brachium (upper arm), antebrachium (forearm) and hand.It 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).

                                

Funcation

The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve.

Clinical Anatomy

The plexus consists of roots, trunks, divisions,cords and branches.

1. ROOTS: These are consititued by the anterior primary rami of spinal nerves C5,6,7,8 and T1 with contributions from the anterior primary rami of C4 and T2. The origin of the plexus may shift one segment either upward or downward resulting in a PRE FIXED PLEUS or POST FIXED PLEXUS respectively. Ina prefixed plexus, the contribution by C4 is large and in that from T2 is often absent. In a post fixed plexus, the contribution by T1 is large, T2 is always present, C4 is absent, and C5 is reduced in size. The roots join to form trunks as follows:

                    

2.TRUNKS: Upper trunk is formed by C5 & C6

                   Middle trunk is formed by C7

                   Lower trunk is formed by C8 & T1

3. DIVISIONS OF THE TRUNKS: Each trunk divides into ventral and dorsal divisions (which ultimately supply the anterior and posterior aspects of the limb). These divisions join to form cords.

4. CORDS:  it forms 3 cords

• The Posterior Cord is formed from the three posterior divisions of the trunks (C5-C8,T1)
• The Lateral Cord is the anterior divisions from the upper and middle trunks (C5-C7)
• The Medial Cord is simply a continuation of the anterior division of the lower trunk (C8,T1)

5. BRANCHES: The specific branches of each cord can be seen at this page