Nerves of the Pectoral Girdle
An amazing network of nerves runs through the shoulder girdle need. The roots of the brachial plexus are formed by the ventral rami of the 5th cervical through the 1st thoracic spinal nerves. The roots combine to form three trunks (superior, middle, and inferior). Each trunk splits to form an anterior and a posterior division. The divisions combine to form lateral, posterior, and medial cords, which in turn become nerves that innervate the structures of the upper extremity:
Dorsal scapular (C5): Originates from the brachial plexus at the 5th cervical root, goes through the middle scalene muscle, and runs to the levator scapulae and rhomboids. It innervates the rhomboids.
Long thoracic (C5–C7): Formed by branches of the 5th, 6th, and 7th cervical roots, runs through the middle scalene muscle into the axillary canal, and innervates the superficial part of the serratus anterior muscle.
Suprascapular (C5–C6): Arises from the superior trunk of the brachial plexus and runs laterally through the scapular notch to innervate the supraspinatus and infraspinatus muscles and the glenohumeral joint.
Nerve to the subclavius (C5): Arises from the superior trunk and runs down past the clavicle to innervate the subclavius muscle and the sternoclavicular joint.
Lateral pectoral (C5–C7): Branches off the lateral cord and runs to the pectoral muscles. It innervates the pectoralis major, but some fibers form a communicating branch to the medial pectoral nerve that innervates the pectoralis minor.
Medial pectoral (C8–T1): This nerve arises from the medial cord and descends lateral to the lateral pectoral nerve. It innervates the pectoralis minor and the sternocostal part of the pectoralis major.
Upper subscapular (C5–C6): This nerve arises from the posterior cord and enters the subscapularis muscle. It innervates the superior portion of the subscapularis.
Lower subscapular (C5–C6): This nerve branches from the posterior cord and passes inferiorly to innervate the inferior portion of the subscapularis and teres major muscles.
Thoracodorsal (C7–C8): Arising from the posterior cord, this nerve runs downward and laterally along the posterior axillary wall to the top of the latissimus dorsi muscle, which it innervates.
Axillary (C5–C6): This nerve arises from the posterior cord and runs through the axillary fossa. It innervates the glenohumeral joint, teres minor, and deltoid muscles.
These branches of the brachial plexus innervate the skin and muscles of the arm and forearm:
Medial cutaneous nerve of the arm (C8, T1): This nerve branches from the medial cord and innervates the skin of the medial arm.
Medial cutaneous nerve of the forearm (C8, T1): This nerve branches from the medial cord and innervates the skin of the medial forearm.
Musculocutaneous nerve (C5–C7): This nerve is a terminal branch of the lateral cord that innervates muscles of the anterior arm and the skin of the lateral forearm.
Median nerve (C5–T1): Forming from branches of the lateral and medial cords, this nerve supplies muscles in the anterior forearm, muscles in the hand, and the skin of the lateral palm.
Ulnar nerve (C8–T1): This nerve is a terminal branch of the medial cord that innervates muscles in the anterior forearm, muscles in the hand, and the skin of the medial hand.
Radial nerve (C5–T1): This nerve is a terminal branch of the posterior cord that innervates the muscle of the posterior arm and posterior forearm, the skin in those regions, and the dorsum of the hand.