brachial plexus

The upper limb is innervated by the brachial plexus located in the neck and axilla, formed by the anterior branches of the four lower cervical spinal nerves (C5,C6,C7,C8) and the first thoracic (T1). The brachial plexus is located lateral to the cervical spine and lies between the anterior and middle scalene muscles, posteriorly and laterally to the sternocleidomastoid muscle.

The plexus passes posterior to the clavicle and follows the
axillary artery under the pectoralis major muscle.

The ventral branches of the fifth and sixth cervical nerves (C5-C6) form the upper trunk; the anterior branch of the seventh cervical nerve (C7) forms the middle trunk; and the anterior branches of the eighth cervical nerve and the first thoracic nerve (C8-T1) form the lower trunk.

The three trunks, located in the supraclavicular fossa, divide into two branches, one anterior and one posterior, which form the fascicles, located around the axillary artery. The anterior branches of the superior and middle trunks form the lateral fasciculus; the anterior branch of the lower trunk forms the medial fasciculus; and the posterior branches of the three trunks form the posterior fasciculus. At the inferior and lateral border of the pectoralis minor muscle, the fascicles subdivide into the terminal branches of the brachial plexus.

BRACHIAL PLEXUS

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

The branches of the brachial plexus can be described as supraclavicular and infraclavicular.

Supraclavicular branches:

• Nerves to the Scalene and Longus Neck Muscles – arise from the ventral rami of the lower cervical nerves (C5, C6, C7, and C8), near their exit from the intervertebral foramina.
• Phrenic Nerve – anterior to the scalene anterior muscle, the phrenic nerve is associated with a branch from the fifth cervical nerve (C5). More details of the phrenic nerve in the Cervical Plexus.
• Dorsal Nerve of Scapula – from the ventral branch of C5, innervates the levator scapulae and the rhomboid muscle.
• Long Thoracic Nerve – It is formed by the branches of C5, C6 and C7 and innervates the serratus anterior muscle.
• Subclavian Muscle Nerve – Originates near the junction of the ventral rami of the fifth and sixth cervical nerves (C5 and C6) and usually communicates with the phrenic nerve and innervates the subclavian muscle.
• Suprascapular nerve – originating from the upper trunk (C5 and C6), innervates the supraspinatus and infraspinatus muscles.

SUPRASCAPULAR, AXILLARY, THORACIDORSAL AND SUBSCAPULAR NERVES

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

Infraclavicular Branches :

These branch from the fascicles, but their fibers can be traced back to the spinal nerves.

The following nerves come from the Lateral Fasciculus :

• Lateral Pectoral – from the branches of the fifth to seventh cervical nerves (C5, C6 and C7). Innervates the deep surface of the pectoralis major muscle;
• Musculocutaneous nerve – derived from the ventral branches of the fifth to seventh cervical nerves (C5, C6 and C7). It innervates the anterior brachii, biceps brachii and coracobrachialis muscles;

MUSCULOCUTANEOUS NERVE

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

• Lateral Root of Median Nerve – derived from the ventral branches of the fifth to seventh cervical nerves (C5, C6 and C7). It innervates the muscles of the anterior forearm and brevis of the thumb, as well as the skin on the lateral side of the hand.

MEDIAN NERVE

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

From the Medial Fasciculus the following nerves come out :

• Medial Pectoral – derived from the ventral branches of the eighth cervical and first thoracic nerves (C8 and T1). Innervates the pectoralis major and minor muscles;
• Medial Cutaneous Nerve of the Forearm – derived from the ventral branches of the eighth cervical and first thoracic nerves (C8 and T1). It innervates the skin over the biceps to near the elbow and runs toward the ulnar side of the forearm to the wrist;
• Medial Cutaneous Nerve of the Arm – which originates from the ventral branches of the eighth cervical and first thoracic nerves (C8,T1). Innervates the medial part of the arm;
• Ulnar nerve – originating from the ventral branches of the eighth cervical and first thoracic nerves (C8 and T1). It innervates the flexor carpi ulnaris, ulnar half of the flexor digitorum profundus, adductor pollicis and deep part of the flexor pollicis brevis. It also innervates the muscles of the hypothenar region, third and fourth lumbricals and all interosseous;

ULNAR NERVE

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

• Medial Root of the Median Nerve – originated from the ventral branches of the eighth cervical and first thoracic nerves (C8 and T1). It innervates the muscles of the anterior forearm and brevis of the thumb, as well as the skin on the lateral side of the hand.
• The following nerves come from the posterior fasciculus :
• Superior Subscapularis – originating from the branches of the fifth and sixth cervical nerves (C5 and C6). Innervates the subscapularis muscle;
• Thoracodorsal Nerve – originated from the branches of the sixth to eighth cervical nerves (C6, C7 and C8). It innervates the latissimus dorsi muscle;
• Inferior Subscapular Nerve – originates from the branches of the fifth and sixth cervical nerves (C5 and C6). Innervates the subscapularis and teres major muscles;
• Axillary Nerve – originates from the branches of the fifth and sixth cervical nerves (C5 and C6). Innervates the deltoid and teres minor muscles;

AXILLARY NERVE

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

• Radial Nerve – originating from the branches of the fifth to eighth cervical nerves and first thoracic nerve (C5, C6, C7, C8 and T1). It innervates the triceps brachii, brachioradialis, extensor carpi radialis longus and brevis, supinator and all muscles in the posterior region of the forearm.

RADIAL NERVE OF THE ARM

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

RADIAL NERVE - FOREARM

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

BRACHIAL PLEXUS SUMMARY

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.