Lateral pectoral nerve

Origin

The lateral pectoral nerve arises from the lateral cord of the brachial plexus, which is formed by the anterior divisions of the upper and middle trunks. It is derived from the C5, C6, and C7 spinal nerve roots. Despite being termed “lateral,” it is named for its origin from the lateral cord rather than its anatomical location.

Course

Proximal Course

After its origin from the lateral cord of the brachial plexus, the lateral pectoral nerve travels anteriorly and medially through the axilla. It initially courses superficial to the axillary artery and the brachial plexus trunks, maintaining a close relationship with the coracoid process of the scapula.

Passage through the Clavipectoral Fascia

The nerve penetrates the clavipectoral fascia (also known as the costocoracoid membrane), which separates the pectoral muscles from the underlying axillary vessels and brachial plexus. After piercing the clavipectoral fascia, it continues its course toward the pectoral muscles.

Branching

The lateral pectoral nerve primarily innervates the pectoralis major muscle but also communicates with the medial pectoral nerve via a loop known as the ansa pectoralis, which provides additional innervation to the pectoralis minor muscle.

• Main Branches: It sends several muscular branches to the pectoralis major, typically innervating the clavicular and upper part of the sternal head of this muscle.
• Communication with Medial Pectoral Nerve: The lateral pectoral nerve sends fibers to the medial pectoral nerve via the ansa pectoralis. This communication allows it to indirectly contribute to the innervation of the pectoralis minor.

Relations

• Proximity to Axillary Vessels: The nerve travels superficial to the axillary artery and axillary vein in the early part of its course.
• Relationship with Pectoral Muscles: The lateral pectoral nerve lies anterior to the axillary vessels and brachial plexus trunks, running deep to the pectoralis major muscle. As it approaches the muscle, it passes between the clavicle and first rib, positioning itself for innervation of the muscle.

Termination

The nerve terminates by innervating the pectoralis major muscle. Through its connection with the medial pectoral nerve (via the ansa pectoralis), it also contributes to the innervation of the pectoralis minor muscle. The branches of the lateral pectoral nerve distribute within the muscle fibers of the pectoralis major, providing motor innervation to the clavicular and upper sternal portions of the muscle.

Function

The lateral pectoral nerve serves a motor function in the upper chest, innervating the pectoral muscles. Its main role is to facilitate the movement of the upper limb through its innervation of the pectoralis major muscle. Additionally, through its communication with the medial pectoral nerve, it plays a supporting role in the innervation of the pectoralis minor muscle.

Motor Innervation

Pectoralis Major Muscle

The lateral pectoral nerve is primarily responsible for innervating the pectoralis major, which is a large, fan-shaped muscle located on the anterior chest wall. The pectoralis major has two heads: the clavicular head and the sternal head.

• Clavicular Head: The lateral pectoral nerve innervates the clavicular head, which plays a key role in the flexion of the arm at the shoulder joint. This is crucial for movements like lifting the arm in front of the body.
• Sternal Head: The lateral pectoral nerve also provides partial innervation to the upper portion of the sternal head. The sternal head helps with the adduction (moving the arm towards the body) and medial rotation of the arm.

Pectoralis Minor Muscle (Indirect Contribution)

Although the lateral pectoral nerve primarily innervates the pectoralis major, it communicates with the medial pectoral nerve through a connection known as the ansa pectoralis. This connection allows the lateral pectoral nerve to contribute to the innervation of the pectoralis minor muscle. The pectoralis minor functions to stabilize the scapula by drawing it inferiorly and anteriorly against the thoracic wall.

Specific Movements Facilitated by the Lateral Pectoral Nerve

• Arm Flexion: The lateral pectoral nerve facilitates flexion of the arm at the shoulder joint through its innervation of the clavicular head of the pectoralis major.
• Arm Adduction: Through its innervation of the sternal head of the pectoralis major, the lateral pectoral nerve aids in bringing the arm toward the body’s midline.
• Medial Rotation of the Arm: The lateral pectoral nerve helps rotate the arm inward, a movement important for tasks like reaching across the body.
• Assisting with Scapular Stabilization: Although indirectly, the lateral pectoral nerve contributes to the stabilization of the scapula through its communication with the medial pectoral nerve, which innervates the pectoralis minor.