Brachial Plexus

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Introduction

The right brachial plexus with its short branches, viewed from in front.

The Brachial Plexus is a network of nerve fibers that run from the spine, passing through the cervico-axillary canal to reach axilla.  It is formed by the ventral rami of the lower four cervical and first thoracic nerve roots (C5-C8, T1). 

Function

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.

Description

Path

The brachial plexus is divided into Roots, Trunks, Divisions, Cords, and Branches. There are five "terminal" branches and numerous other "pre-terminal" or "collateral" branches that leave the plexus at various points along its length.

• The five Roots are the five anterior rami of the of the lower four cervical and first thoracic nerve roots (C5-C8, T1), after they have given off their segmental supply to the muscles of the neck.
• These Roots merge to form three Trunks:
  • Upper Trunk (C5-C6)
  • Middle Trunk (C7)
  • Lower Trunk (C8, T1)
• Each Trunk then splits into anterior and posterior divisions, to form six Divisions.   The anterior/ posterior divisions innervate flexor groups versus extensor groups:
  • anterior divisions of the upper, middle, and lower trunks
  • posterior divisions of the upper, middle, and lower trunks
• These six Divisions will regroup to become the three Cords. The Cords are named by their position with respect to the axillary artery.
  • 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)

Anatomical illustration of the brachial plexus with areas of roots, trunks, divisions and cords marked.

Specific Branches

The branches are listed below. Most branch from the cords, but a few branch (indicated in italics) directly from earlier structures.

Bold indicates primary spinal root component of nerve. Italics indicate spinal roots that frequently, but not always, contribute to the nerve.

From	Nerve	Roots	Muscles	Cutaneous
roots	Dorsal scapular nerve	C4, C5	Rhomboid muscles and Levator scapulae	-
roots	Long thoracic nerve	C5, C6, C7	Serratus anterior	-
upper trunk	Nerve to the subclavius	C5, C6	Subclavius muscle	-
upper trunk	Suprascapular nerve	C5, C6	Supraspinatus and Infraspinatus	-
lateral cord	Lateral pectoral nerve	C5, C6, C7	Pectoralis major and Pectoralis minor (by communicating with the Medial pectoral nerve)	-
lateral cord	Musculocutaneous nerve	C5, C6, C7	Coracobrachialis, Brachialis and Biceps brachii	becomes the Lateral cutaneous nerve of the forearm
lateral cord	lateral root of the Median nerve	C6, C7	fibres to the median nerve	-
posterior cord	Upper subscapular nerve	C5, C6	Subscapularis (upper part)	-
posterior cord	Thoracodorsal nerve (middle subscapular nerve)	C6, C7, C8	Latissimus dorsi	-
posterior cord	Lower subscapular nerve	C5, C6	subscapularis (lower part ) and Teres major	-
posterior cord	Axillary nerve	C5, C6	anterior branch: deltoid and a small area of overlying skin posterior branch: Teres minor and deltoid muscles	posterior branch becomes Upper lateral cutaneous nerve of the arm
posterior cord	Radial nerve	C5, C6, C7, C8, T1	Triceps brachii, Supinator, Anconeus, the extensor muscles of the Forearm, and Brachioradialis	skin of the posterior arm as the Posterior cutaneous nerve of the arm
medial cord	Medial pectoral nerve	C8, T1	Pectoralis major and Pectoralis minor	-
medial cord	medial root of the Median nerve	C8, T1	fibres to the median nerve	portions of hand not served by ulnar or radial
medial cord	Medial cutaneous nerve of the arm	C8, T1	-	front and medial skin of the Arm
medial cord	Medial cutaneous nerve of the forearm	C8, T1	-	medial skin of the forearm
medial cord	Ulnar nerve	C8, T1	Flexor carpi ulnaris, the medial two bellies of Flexor digitorum profundus, the intrinsic hand muscles except the Thenar muscles and the two most lateral lumbricals	the skin of the medial side of the hand and medial one and a half fingers on the palmar side and medial two and a half fingers on the dorsal side

Specific branches can be visualised on the diagram below:

Injuries

Injury to the brachial plexus can be very problematic because the nerves branching off of the plexus provide innervation to the upper extremity. Clinical signs and symptoms vary with which area of the plexus is involved, and can generally result in paralysis or anesthesia. Brachial plexus injury can occur in a variety of ways. During birth, excessive stretching of the neck or pulling the upper extremity can result in an upper brachial plexus injury or inferior trunk, respectively. An adult can injury the brachial plexus by landing on the neck in a way that separates the neck from the shoulder, or from a traction injury.

The most common forms of injury include Erb Palsy (upper brachial plexus palsy) and Klumpke’s Palsy (lower brachial plexus injury). The characteristics of Erb Palsy include a waiter’s tip position (arm lies in internal rotation, elbow extended, forearm pronated, wrist and fingers flexed). The characteristics of Klumpke’s Palsy include paralysis and atrophy of the hand muscles and flexors of the wrist.

Brachial Plexus Block

A brachial plexus block allows a surgeon to operate on an upper extremity without the use of a general anesthetic, when combined with a tourniquet. The location of the injection is between the posterior border of the sternocleidomastoid and the clavicle. The axillary sheath surrounds the axillary vein, axillary artery, and three cords of the brachial plexus. When the injection takes effect, the muscles and skin innervated by the cords found in the sheath are anesthetized.

Other Important Information

A useful mnemonic to remember the path of the brachial plexus is Randy (Roots) Travis (Trunks) Drinks (Divisions) Cold (Cords) Beer (Branches).

Resources

Useful websites/ more information: Learning the Brachial Plexus, BP Video 1, BP Video 2, Brachial Plexus Block

Recent Related Research

Jepsen JR, Laursen LH, Hagert CG, Kreiner S, Larsen AI. Diagnostic accuracy of the neurological upper limb examination I: Inter-rater reproducibility of selected findings and patterns. BMC Neurology. 2006;6(8).

Jepsen JR, Laursen LH, Hagert CG, Kreiner S, Larsen AI.  Diagnostic accuracy of the neurological upper limb examination II: Relations to symptoms of patterns of findings.  BMC Neurol. 2006;6(10).  

Dahlin LB, Blackman C, Duppe H, Saito H, Chemnitz A, Abul-Kasim K, Maly P. Compression of the lower trunk of the brachial plexus by a cervical rib in two adolescent girls: case reports and surgical treatment. J Brachial Plex Peripher Nerve Inj. 2009;4(14).

Feinberg JH, Radecki J, Wolfe SW, Strauss HL, Mintz DN. Brachial Plexopathy/ Nerve Root Avulsion in a football player: The role of electrodiagnostics. HSSJ. 2008;4(1):87-95.

Jepsen JR. Upper limb neuropathy in computer operators? A clinical study of 21 patients. BMC Musculoskelet Disord. 2004;5(26).

Monreal R. Restoration of elbow flexion by transfer of the phrenic nerve to musculocutaneous nerve after brachial plexus injuries. HAND. 2007;2:206-211.

Montreal R. Steindler flexorplasty to restore elbow flexion in C5-C6-C7 brachial plexus palsy type. J Brachial Plex Peripher Nerve Inj. 2007;2(15).

Rohde RS, Scott WW. Nerve transfers for adult traumatic brachial plexus palsy (Brachial Plexus Nerve Transfer). HSSJ. 2007:3:77-82.

Saliba S, Saliba EN, Pugh KF, Chhabra A, Diduch D. Rehabilitation considerations of a brachial plexus injury with complete avulsion of C5 and C6 nerve roots in a colege football player: A Case Study. Sports Health. 2009:1(5): 370-375.

Yamazaki H, Doi K, Hattori Y, Sakamoto S. Computerized tomography myelography with coronal and oblique coronal view for diagnosis of nerve root avulsion in brachial plexus injury. J Brachial Plex Periph Nerve Inj. 2007;2:16.

Recent Related Research (from Pubmed)

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References

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