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 root, specifically from the nerve root above the fifth cervical vertebra to the nerve root below the first thoracic vertebra (C5-T1). It proceeds through the neck, the axilla (armpit region), and into the arm. [edit] 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 intercostobrachialis nerve. Because the majority of the upper limb muscles are innervated by the brachial plexus, lesions can lead to severe functional impairment.[1] [edit] Anatomy One can remember the order of brachial plexus elements by way of the mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Real Teenagers Drink Cold Beer") - Roots, Trunks, Divisions, Cords, Branches[2] or - Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and (Terminal) Branches. - 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 with 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".
[edit] Diagram [edit] 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 | [edit] Additional images  Brachial plexus with areas of roots, trunks, divisions and cords marked.  Mind map showing branches of Brachial plexus Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. | The axillary artery and its branches. | Cutaneous nerves of right upper extremity. | Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. | The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses. | Side of neck, showing chief surface markings. | Brachial plexus with areas of roots, trunks, divisions and cords marked. | [edit] See also [edit] References - ^ Moore, K.L., & Agur, A.M. (2007). Essential Clinical Anatomy: Third Edition. Baltimore: Lippincott Williams & Wilkins. 434-435. ISBN 9780781762748
- ^ Mnemonic at medicalmnemonics.com 18 2741
[edit] External links | Nerves: spinal nerves (TA A14.2, GA 9.916) | | | Cervical (8) | C1, C2, C3, C4, C5, C6, C7, C8 anterior ( Cervical plexus, Brachial plexus) - posterior ( Posterior branches of cervical nerves, Suboccipital - C1, Greater occipital - C2, Third occipital - C3) | | | Thoracic (12) | T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12 anterior ( Intercostal, Intercostobrachial - T2, Thoraco-abdominal nerves - T7-T11, Subcostal - T12) - posterior ( Posterior branches of thoracic nerves) | | | Lumbar (5) | | | | Sacral (5) | | | | Coccygeal (1) | | | |
