Brachial plexus
Updates to Article Attributes
The brachial plexus is a complex neural network formed by lower cervical and upper thoracic ventral nerve roots andwhich supplies motor and sensory innervation to the upper limb and pectoral girdle. It is located in the neck extending into the axilla posterior to the clavicle.
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. Or alternatively the roots emerge to form 3 trunks between the scalenus anterior and medius muscles, the trunks divide into 6 divisions which pass behind the mid clavicle, the divisions contribute to 3 cords which surround the second part of the axillary artery and the cords terminate as the 5 major nerves.
- major (terminal) 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. This mnemonic describes the order of these subdivisions.
Roots
Roots are formed behindbetween scalenus anterior byand scalenus medius muscles by the anterior rami of C5-C8 and T1 nerve roots. Three branches arise from the roots directly 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 (although some texts describe this nerve arising from the superior trunk 4)
- long thoracic nerve: arises from the posterior aspects of C5-C7 and supplies serratus anterior
In addition, the scaleni and longus colli muscles are supplied by multiple variable unnamed muscular branches thatarise from all or some of the roots 4.
It is important to remember that the dorsal rami course posteriorly into the spinal extensors (erector spinae) and do not contribute to the brachial plexus.
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 roots combine to form the upper
trunkor superior trunk - C7
makesroot makes up the middle trunk - C8 and T1 roots combine to form the lower or inferior trunk
One branch arises from the trunks 2:
- suprascapular nerve - arises from the upper trunk and supplies the supraspinatus and infraspinatus muscles, and
thesensation to the glenohumeral and acromioclavicular joints
Divisions
Each trunk divides to form an anterior and posterior division behindposterior to the mid clavicle 2.In general anterior divisions supply muscles of the anterior compartments (flexors) whereas the posterior divisions supply muscles of the posterior compartments (extensors) 4.
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
-
terminal branches
- musculocutaneous nerve
- lateral root of the median nerve
Branches from the medial cord are2:medial pectoral nerve-
medial root of themedian nerve medial cutaneous nerve of the armmedial cutaneous nerve of the forearmulnar nerve
Branches from the posterior cord are 2:
- upper subscapular nerve
- thoracodorsal nerve
- lower subscapular nerve
- terminal branches
Branches from the medial cord are 2:
- medial pectoral nerve
- medial cutaneous nerve of the arm
- medial cutaneous nerve of the forearm
-
terminal branches
- medial root of the median nerve
- ulnar nerve
Some authors describe the medial and lateral pectoral nerves arising from shared branches from the medial and lateral cords (as indicated in the diagram).
Variant anatomy
-
approximatelyApproximately 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 (i.e. the roots are moved up one vertebral level)
-
post-fixed brachial plexus: contribution from T2 ventral ramus, with overall contribution from C6-T2 (i.e. the roots are moved down one vertebral level)
- the inferior trunk is at risk of compression by the first rib
- contributions of C4 or T2 ventral rami (6 or 7 roots)
- trunk, divisions or cord may be absent
- variations in branching patterns of the cords have also been reported 1
Related pathology
-<p>The <strong>brachial plexus </strong>is formed by lower cervical and upper thoracic ventral nerve roots and supplies motor and sensory innervation to the upper limb and pectoral girdle.</p><h4>Summary</h4><ul>- +<p>The <strong>brachial plexus </strong>is a complex neural network formed by lower cervical and upper thoracic ventral nerve roots which supplies motor and sensory innervation to the upper limb and pectoral girdle. It is located in the neck extending into the axilla posterior to the clavicle.</p><h4>Summary</h4><ul>
-<strong>course:</strong> emerges between <a href="/articles/scalenus-anterior-muscle-1">anterior</a> and <a href="/articles/middle-scalene">middle scalenes</a>, courses through the posterior triangle of neck posterior to the <a href="/articles/clavicle">clavicle</a> before becoming closely associated with the <a href="/articles/axillary-artery">axillary artery</a> in the <a href="/articles/axilla">axilla</a> before giving up its terminal branches</li>- +<strong>course:</strong> emerges between <a href="/articles/scalenus-anterior-muscle-1">anterior</a> and <a href="/articles/middle-scalene">middle scalenes</a>, courses through the posterior triangle of neck posterior to the <a href="/articles/clavicle">clavicle</a> before becoming closely associated with the <a href="/articles/axillary-artery">axillary artery</a> in the <a href="/articles/axilla">axilla</a> before giving up its terminal branches. Or alternatively the roots emerge to form 3 trunks between the scalenus anterior and medius muscles, the trunks divide into 6 divisions which pass behind the mid clavicle, the divisions contribute to 3 cords which surround the second part of the axillary artery and the cords terminate as the 5 major nerves.</li>
-<strong>major branches</strong><ul>- +<strong>major (terminal) branches</strong><ul>
-</ul><h4>Gross anatomy</h4><p>The brachial plexus consists of roots, trunks, divisions, cords and terminal branches as it travels from proximal to distal upper limb. This <a title="mnemonic" href="/articles/brachial-plexus-root-order-mnemonic">mnemonic</a> describes the order of these subdivisions.</p><h5>Roots</h5><p>Roots are formed behind scalenus anterior by the anterior rami of C5-C8 and T1. Three branches arise from the roots <sup>2</sup>:</p><ul>- +</ul><h4>Gross anatomy</h4><p>The brachial plexus consists of roots, trunks, divisions, cords and terminal branches as it travels from proximal to distal upper limb. This <a href="/articles/brachial-plexus-root-order-mnemonic">mnemonic</a> describes the order of these subdivisions.</p><h5>Roots</h5><p>Roots are formed between scalenus anterior and scalenus medius muscles by the anterior rami of C5-C8 and T1 nerve roots. Three branches arise from the roots directly <sup>2</sup>:</p><ul>
-<li>subclavian nerve: arises from the C5 and C6 roots anteriorly to supply subclavius</li>- +<li>subclavian nerve: arises from the C5 and C6 roots anteriorly to supply subclavius (although some texts describe this nerve arising from the superior trunk <sup>4</sup>)</li>
-</ul><h5>Trunks</h5><p>Trunks form from the roots as they pass between <a href="/articles/scalenus-anterior-muscle-1">scalenus anterior</a> and <a href="/articles/scalenus-medius-muscle">medius muscles</a>, then go on to traverse the posterior triangle:</p><ul>-<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>-</ul><p>One branch arises from the trunks <sup>2</sup>:</p><ul><li>suprascapular nerve - arises from the upper trunk and supplies the <a href="/articles/supraspinatus-muscle-and-tendon">supraspinatus</a> and <a href="/articles/infraspinatus">infraspinatus muscles</a>, and the <a href="/articles/glenohumeral-joint">glenohumeral</a> and <a href="/articles/acromioclavicular-joint-1">acromioclavicular joints</a>-</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>- +</ul><p>In addition, the scaleni and longus colli muscles are supplied by multiple variable unnamed muscular branches that<em> </em>arise from all or some of the roots <sup>4</sup>.</p><p>It is important to remember that the dorsal rami course posteriorly into the spinal extensors (erector spinae) and do not contribute to the brachial plexus.</p><h5>Trunks</h5><p>Trunks form from the roots as they pass between <a href="/articles/scalenus-anterior-muscle-1">scalenus anterior</a> and <a href="/articles/scalenus-medius-muscle">medius muscles</a>, then go on to traverse the posterior triangle:</p><ul>
- +<li>C5 and C6 roots combine to form the upper or superior trunk</li>
- +<li>C7 root makes up the middle trunk</li>
- +<li>C8 and T1 roots combine to form the lower or inferior trunk</li>
- +</ul><p>One branch arises from the trunks <sup>2</sup>:</p><ul><li>suprascapular nerve - arises from the upper trunk and supplies the <a href="/articles/supraspinatus-muscle-and-tendon">supraspinatus</a> and <a href="/articles/infraspinatus">infraspinatus muscles</a>, and sensation to the <a href="/articles/glenohumeral-joint">glenohumeral</a> and <a href="/articles/acromioclavicular-joint-1">acromioclavicular joints</a>
- +</li></ul><h5>Divisions</h5><p>Each trunk divides to form an anterior and posterior division posterior to the mid <a href="/articles/clavicle">clavicle</a> <sup>2</sup>.<sup> </sup>In general anterior divisions supply muscles of the anterior compartments (flexors) whereas the posterior divisions supply muscles of the posterior compartments (extensors) <sup>4</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>
-</ul><p>The <a href="/articles/prevertebral-fascia">prevertebral fascia</a> 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 <sup>3</sup>.</p><h5>Peripheral nerves</h5><p>Various peripheral nerves then branch from these cords. Branches from the lateral cord are <sup>2</sup>:</p><ul>- +</ul><p>The <a href="/articles/prevertebral-fascia">prevertebral fascia</a> 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 <sup>3</sup>.</p><h5>Peripheral nerves</h5><p>Various peripheral nerves then branch from these cords.</p><p>Branches from the<strong> lateral cord </strong>are <sup>2</sup>:</p><ul>
- +<li>terminal branches<ul>
-</ul><p>Branches from the medial cord are <sup>2</sup>:</p><ul>-<li>medial pectoral nerve</li>-<li>medial root of the <a href="/articles/median-nerve">median nerve</a>- +</ul>
-<li>medial cutaneous nerve of the arm</li>-<li>medial cutaneous nerve of the forearm</li>-<li><a href="/articles/ulnar-nerve">ulnar nerve</a></li>-</ul><p>Branches from the posterior cord are <sup>2</sup>:</p><ul>- +</ul><p>Branches from the <strong>posterior cord</strong> are <sup>2</sup>:</p><ul>
- +<li>terminal branches<ul>
-</ul><h4>Variant anatomy</h4><ul>-<li>approximately 50% of the population show significant variation in formation of the brachial plexus<ul>- +</ul>
- +</li>
- +</ul><p>Branches from the <strong>medial cord </strong>are <sup>2</sup>:</p><ul>
- +<li>medial pectoral nerve</li>
- +<li>medial cutaneous nerve of the arm</li>
- +<li>medial cutaneous nerve of the forearm</li>
- +<li>terminal branches<ul>
- +<li>medial root of the <a href="/articles/median-nerve">median nerve</a>
- +</li>
- +<li><a href="/articles/ulnar-nerve">ulnar nerve</a></li>
- +</ul>
- +</li>
- +</ul><p>Some authors describe the medial and lateral pectoral nerves arising from shared branches from the medial and lateral cords (as indicated in the diagram).</p><h4>Variant anatomy</h4><p>Approximately 50% of the population show significant variation in formation of the brachial plexus:</p><ul>
-<strong>pre-fixed brachial plexus:</strong> contribution from C4 ventral ramus, with overall contribution from C4-C8</li>- +<strong>pre-fixed brachial plexus:</strong> contribution from C4 ventral ramus, with overall contribution from C4-C8 (i.e. the roots are moved up one vertebral level)</li>
-<strong>post-fixed brachial plexus:</strong> contribution from T2 ventral ramus, with overall contribution from C6-T2</li>-</ul>- +<strong>post-fixed brachial plexus:</strong> contribution from T2 ventral ramus, with overall contribution from C6-T2 (i.e. the roots are moved down one vertebral level)<ul><li>the inferior trunk is at risk of compression by the first rib</li></ul>
- +<li>contributions of C4 or T2 ventral rami (6 or 7 roots)</li>
- +<li>trunk, divisions or cord may be absent</li>
- +<li><a title="Thoracic outlet syndrome" href="/articles/thoracic-outlet-syndrome">thoracic outlet syndrome</a></li>
- +<li><a title="Klumpke palsy" href="/articles/klumpke-palsy">Klumpke palsy</a></li>
- +<li> </li>
References changed:
- 4. Moore KL, Agur AMR, Dalley AF. Clinically oriented anatomy. LWW. ISBN:1451119453. <a href="http://books.google.com/books?vid=ISBN1451119453">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/1451119453">Find it at Amazon</a><span class="auto"></span>
Tags changed:
- anatomy