Although only part of the brachial plexus is found in the axilla, we will present a general layout of the plexus before covering the parts that are found in the axilla. Whoever first described the brachial plexus must have been a nature lover, or at least a tree lover, because the various parts of the plexus are named according to various parts of a tree, starting from the roots.
| The brachial plexus starts in the neck from the ventral rami of spinal
nerves C5 - T1 (5th cervical to 1st thoracic spinal cord segments). These
rami are called roots. The roots will continue through the neck and, some
of them merge, to form trunks. C5 and C6 form the upper trunk, C7 continues
as the middle trunk and C8 and T1 for the lower trunk. While still in the
neck, the trunks divide into anterior and posterior divisions. The divisions
then reunite in different patterns. The anterior divisions of the upper
and middle trunks merge to form the lateral cord. The anterior division
of the lower trunk continues as the medial cord. The posterior divisions
of all trunks merge to form the posterior cord. At this point, the cords
are in the axilla. The cords are named according to their relationship
with the axillary artery. Medial to it, lateral to it or posterior to it.
Finally, the cords give rise to various branches that supply the upper
limb structures. I want to point out that although most of the branches
to the upper limb muscles arise from the plexus in the axilla, some
arise from the cervical (neck) part of the plexus. These nerves are the
dorsal scapular, nerve to subclavius, long thoracic, and suprascapular.
Needless to say, the brachial plexus is a very important structure in the axilla and can be injured here through various types of trauma (athletic injuries, humeral dislocations, crutch injuries, surgical injuries), carcinomas and other pathological problems. |
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Branches of Brachial Plexus |
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| Roots | Trunks | Cords | |||
| Lateral | Medial | Posterior | |||
| dorsal scapular (2)
long thoracic (1) nerve to subclavius (3) |
suprascapular (4) | lateral pectoral (5)
lateral head of median n. (6) musculocutaneous |
medial pectoral (8)
medial cutaneous of arm (9) medial cutaneous of forearm(10) medial head of median n.(11) ulnar(12) |
upper subscapular(14)
thoracodorsal(15) lower subscapular axillary(17) radial(18) |
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Axillary Arteries & Veins |
 Axillary Lymph Nodes |
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This is copyrighted©1999 by Wesley Norman, PhD, DSc |