Brachial plexus

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Nerve: Brachial plexus
Image:Brachial plexus.gif
Brachial plexus
Latin	plexus brachialis
Gray's	subject #210 930
From	C5-T1
MeSH	A08.800.800.720.050
Dorlands/Elsevier	p_24/12647576

The brachial plexus is an arrangement of nerve fibres (a plexus) running from the spine (vertebrae C5-T1), through the neck, the axilla (armpit region), and into the arm. 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 and an area of skin near the axilla innervated by the intercostobrachialis nerve. Therefore, lesions of the plexus can lead to severe functional impairment.

1 Anatomy
- 1.1 Path
- 1.2 Specific branches
2 Injuries
3 Additional images
4 See also

[edit] Anatomy

[edit] Path

The brachial plexus starts from the five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck. These are the five roots.

These roots merge to form three trunks: "superior" or "upper" C5-C6, "middle" C7, and "inferior" or "lower" C8-T1.

Each trunk then splits to form an anterior and a posterior division.

These six divisions will regroup to become the cords. The cords are named by their position in respect to the axillary artery.

The posterior cord is formed from the three posterior divisions of the trunks. (C5-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 lower trunk. (C8-T1)

One can remember the order of brachial plexus elements by way of the mnemonic, "Randy Travis Drinks Cold Beer" - Roots, Trunks, Divisions, Cords, Branches

[edit] Specific branches

From	Nerve	Source	Supplies
roots	Dorsal scapular nerve	C5	rhomboid muscles and levator scapulae
trunks	Nerve to the subclavius	C5, C6	subclavius muscle
roots	Long thoracic nerve	C5, C6, C7	serratus anterior
trunks	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. (It then becomes the lateral cutaneous nerve of the forearm.)
lateral cord	Lateral root of the median nerve	C5, C6, C7	fibres to the median nerve
posterior cord	Upper subscapular nerve	C5, C6	subscapularis (upper part)
posterior cord	Thoracodorsal nerve	C6, C7, C8	latissimus dorsi
posterior cord	Lower subscapular nerve	C5, C6	lower part of subscapularis 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 (then becomes the upper lateral cutaneous nerve of the arm)
posterior cord	Radial nerve (largest nerve of the plexus)	C5, C6, C7, C8, T1	triceps brachii, the skin of the posterior arm as the posterior cutaneous nerve of the arm, anconeus, the extensor muscles of the forearm, and brachioradialis.
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.
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 2 bellies of flexor digitorum profundus, most of the small muscles of the hand and 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.

[edit] Injuries

Image:Gray813.png Image:Gray811.png	Image:Gray814.png Image:Gray812.png
Nerves of the arms.

Brachial plexus lesions are classified as traumautic or obstetric. These typically result from excessive stretching and avulsion injury. Traumatic injuries are often caused by high-velocity motor vehicle accidents, especially in motorcyclists. Injury from a direct blow to the lateral side of the scapula is also possible.

Most commonly, forceps delivery or falling on the neck at an angle causes upper plexus lesions (Erb's Palsy). This type of injury produces a very characteristic sign called Waiter's tip deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles.

Much less frequently, sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) produces a lower plexus injury. This results in the sign known as clawed hand due to loss of function of the ulnar nerve and the intrinsic muscles of the hand it supplies.

The cardinal signs of brachial plexus avulsion are:

a weakness in the arm
diminished reflexes
corresponding sensory deficits

In most cases the nerve roots are stretched or torn from their origin, since the meningeal coverings of the nerve roots are thinner than the sheaths enclosing the peripheral nerves. The epineurium of the peripheral nerve is contiguous with the dural mater, providing extra support to the peripheral nerves. In cases where the nerve roots have been torn, recovery is unlikely without invasive experimental surgical techniques ^{[citation needed]}.

The diagnosis may be confirmed by an EMG examination in 5-7 days. The evidence of denervation will be evident. If there is no nerve conduction 72 hours after the injury, then avulsion is most likely.