Brachial plexus
Updates to Article Attributes
The brachial plexus is formed by lower cervical and upper thoracic ventral nerve roots and supplies motor and sensory innervation to the upper limb and pectoral girdle.
Summary
- origin: ventral rami of C5 to T1
- course: emerges between anterior and middle scalenes, courses through the posterior triangle of neck posterior to the clavicle before becoming closely associated with the axillary artery in the axilla before giving up its terminal branches
- major branches
- motor supply: upper limb and pectoral girdle
- sensory supply: upper limb and part of the upper thorax
Gross anatomy
The brachial plexus consists of roots, trunks, divisions, cords and terminal branches as it travels from proximal to distal upper limb.
Roots
Roots are formed behind scalenus anterior by the anterior rami of C5-C8 and T1. Three branches arise from the roots 2:
- dorsal scapular nerve: arises from the posterior aspect of the C5 root and supplies the rhomboids
- subclavian nerve: arises from the C5 and C6 roots anteriorly to supply subclavius
- long thoracic nerve: arises from the posterior aspects of C5-C7 and supplies serratus anterior
Trunks
Trunks form from the roots as they pass between scalenus anterior and medius muscles, then go on to traverse the posterior triangle:
- C5 and C6 combine to form the upper trunk
- C7 makes up the
middlemiddle trunk - C8 and T1 combine to form the
lowerlower trunk
One branch arises from the trunks 2:
- suprascapular nerve - arises from the upper trunk and supplies the supraspinatus and infraspinatus muscles, and the glenohumeral and acromioclavicular joints
Divisions
Each trunk divides to form an an anterior
Cords
The divisions then combine to form cords, which are named for their relation to the second part of the axillary artery 2:
- lateral cord is formed by the union of the upper two anterior divisions at the lateral border of the first rib
- medial cord is a continuation of the lower anterior division
- posterior cord consists of the united three posterior divisions
The prevertebral fascia of the neck extends down to ensheath the axillary artery and cords. It is into this axillary sheath that local anaesthetic is injected when performing a brachial plexus block 3.
Peripheral nerves
Various peripheral nerves then branch from these cords. Branches from the lateral cord are 2:
- lateral pectoral nerve
- musculocutaneous nerve
- lateral root of the median nerve
Branches from the medial cord are 2:
- medial pectoral nerve
- medial root of the median nerve
- medial cutaneous nerve of the arm
- medial cutaneous nerve of the forearm
- ulnar nerve
Branches from the posterior cord are 2:
- upper subscapular nerve
- thoracodorsal nerve
- lower subscapular nerve
- radial nerve
- axillary nerve
Variant anatomy
Approximately 50% of the population show significant variation in formation of the brachial plexus:
- pre-fixed brachial plexus: contribution from C4 ventral ramus, with overall contribution from C4-C8
- post-fixed brachial plexus: contribution from T2 ventral ramus, with overall contribution from C6-T2
Related pathology
-<li>C5 and C6 combine to form the <strong>upper trunk</strong>-</li>-<li>C7 makes up the <strong>middle trunk</strong>-</li>-<li>C8 and T1 combine to form the <strong>lower trunk</strong>-</li>- +<li>C5 and C6 combine to form the upper trunk</li>
- +<li>C7 makes up the middle trunk</li>
- +<li>C8 and T1 combine to form the lower trunk</li>
-</li></ul><h5>Divisions</h5><p>Each trunk divides to form an an <strong>anterior</strong> and <strong>posterior division</strong> behind the <a href="/articles/clavicle">clavicle</a> <sup>2</sup>.</p><h5>Cords</h5><p>The divisions then combine to form cords, which are named for their relation to the second part of the <a href="/articles/axillary-artery">axillary artery</a> <sup>2</sup>:</p><ul>- +</li></ul><h5>Divisions</h5><p>Each trunk divides to form an anterior and posterior division behind the <a href="/articles/clavicle">clavicle</a> <sup>2</sup>.</p><h5>Cords</h5><p>The divisions then combine to form cords, which are named for their relation to the second part of the <a href="/articles/axillary-artery">axillary artery</a> <sup>2</sup>:</p><ul>
-<li><a href="/articles/erbs-palsy-1">Erb's palsy</a></li>- +<li><a href="/articles/erbs-palsy-1">Erb palsy</a></li>
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