medial cord of brachial plexus

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Brachial plexus

The brachial plexus is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve roots, specifically from above the fifth cervical vertebra to underneath the first thoracic vertebra (C5-T1). It proceeds through the neck, the axilla (armpit region) and into the arm.

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 and an area of skin near the axilla innervated by the intercostobrachialis nerve.

Therefore, brachial plexus lesions can lead to severe functional impairment.

Anatomy

Path

One can remember the order of brachial plexus elements by way of the mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Randy Travis Drinks Cold Blood") - Roots, Trunks, Divisions, Cords, Branches or - Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and (Terminal) Branches.

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

These roots merge to form three trunks:

"superior" or "upper" (C5-C6)
"middle" (C7)
"inferior" or "lower" (C8-T1)

Each trunk then splits in two, to form six divisions:

anterior division of the upper, middle and lower trunks
posterior division of the upper, middle, and lower trunks

These six divisions will regroup to become the three 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 anterior division of the lower trunk (C8-T1)

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

Diagram

Specific branches

One can remember the specific branches of lateral, posterior and medial cord using the mnemonic LML ULNAR M4U respectively.

LML - lateral pectoral nerve , musculocutaneous nerve , lateral root of the median nerve.
ULNAR - upper subscapular nerve , lower subscapular nerve , nerve to latissmus dorsi (thoracodorsal nerve) , axillary nerve , radial nerve.
M4U - medial pectoral nerve , medial root of the median nerve , medial cutaneous nerve of the arm , medial cutaneous nerve of the forearm , ulnar nerve.

From	Nerve	Roots	Muscles	Cutaneous
roots	dorsal scapular nerve	C5	rhomboid muscles and levator scapulae	-
roots	long thoracic nerve	C5, C6, C7	serratus anterior	-
superior trunk	nerve to the subclavius	C5, C6	subclavius muscle	-
superior trunk	suprascapular nerve	C5, C6	supraspinatus and infraspinatus	-
lateral cord	lateral pectoral nerve	C5, C6, C7	pectoralis major (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	C5, 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 2 bellies of flexor digitorum profundus, most of the small muscles of the hand	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