Overview
Do not be
daunted by the brachial plexus! It is simply the nerve plexus of the upper limb
and is one of the easiest to learn. The five major branches are the
musculocutaneous, radial, axillary, ulnar, and median nerves. As long as you
focus on these five main branches, you will not go wrong. The plexus runs in
the axilla and innervates the muscles and skin of the upper limb.
Gross Anatomy
The
brachial plexus is formed by the ventral rami of the C5-T1 spinal nerves. It
emerges between the anterior and middle scalene muscles, and runs in the
axilla, where the cords of the plexus surround the axillary artery, which is
reflected in their names. It is divided into roots (C5-T1), trunks (upper,
middle and lower), divisions, cords (medial, lateral and posterior), and
branches (5 main branches are the radial, axillary, musculocutaneous, ulnar and
median).
The mixed
spinal nerves emerge from the intervertebral foramen. The C4 and C5 roots give
rise to the dorsal scapular nerve (supplies infraspinatus and supraspinatus),
C5, 6 and 7 give rise to the long thoracic nerve (supplies serratus anterior),
and the C5 nerve root contributes to the phrenic nerve (supplies the
diaphragm).
C5 and C6
merge to form the upper trunk, C7 continues alone, C8 and T1 merge to form the
lower trunk. Each of these trunks gives a branch which all merge to form the
posterior cord (lies posterior to the axillary artery). Once these posterior cord-forming
branches have been given off, the upper trunk continues as the lateral cord,
and the lower trunk continues as the medial cord.
The
posterior cord gives rise to the radial nerve (supplies the extensor
compartment of the arm and forearm, as well as sensation over the posterior
surface of the arm and hand), the axillary nerve (supplies teres minor and
deltoid muscles, also supplies sensation to the regimental patch C5 dermatome),
the thoracodorsal nerve (motor supply to the latissimus dorsi muscle), and the
upper and lower subscapular nerves (both supply subscapularis, and the lower
also supplies teres major).
The medial
cord gives rise to the ulnar nerve (supplies flexor carpi ulnaris and the ulnar
head of flexor digitorum profundus in the forearm, and in the hand supplies the
interossei, adductor pollicis brevis and medial two lumbricals). The medial
cord also gives rise to the medial cutaneous nerves of the arm and forearm as
well as the medial pectoral nerve (which supplies the pectoral muscles, mainly
pectoralis minor). It also gives a branch to form the median nerve.
The
lateral cord gives rise to the musculocutaneous nerve (supplies the flexor
compartment of the arm, as well as the sensation to the lateral forearm). The
lateral pectoral nerve also arises from the cord, and supplies the pectoral
muscles (mainly pectoralis major). It also gives a branch to form the median
nerve.
Clinical Anatomy
Quick Anatomy
Key Facts
Developmental precursor- Alar and
basal plate of C5-T1 spinal nerves
Origin- C5-T1
Branches-
From the roots- Long thoracic nerve,
suprascapular nerve, dorsal scapular nerve
Medial cord- Ulnar nerve, medial
cutaneous nerve of the arm, medial cutaneous nerve of the forearm, medial
branch to form the median nerve, medial pectoral nerve
Lateral cord- Musculocutaneous
nerve, lateral pectoral nerve, lateral branch to form the median nerve
Posterior cord- Radial nerve,
axillary nerve, upper subscapular nerve, lower subscapular nerve, thoracodorsal
nerve
Muscles supplied- All muscles of the
upper limb, scapular region, pectoral region, and the serratus anterior muscle
of the superolateral thorax.
Dermatome- All of the upper limb.
Aide-Memoire
Place your
hand against your axilla with your fingers pointing towards your hand, the
position of your five fingers reflects the position of the five main branches
of the plexus.