Long thoracic nerve

Origin and course

The long thoracic nerve is a lateral branch of the brachial plexus, which arises from the anterior rami of spinal nerves C5, C6 and C7. These nerve roots commence deep to the scalenus medius muscle to form the trunk of the long thoracic nerve. Due to its relatively superficial location, almost the entire course of the nerve is easily visible in cadavers. Upon arising, the trunk of the nerve descends posteriorly to the brachial plexus, axillary artery and axillary vein, and anteriorly to the scalenus posterior muscle.

The long thoracic nerve courses distally and laterally, deep to the clavicle and superficial to the first and second ribs. It continues along the anterior thoracic wall in the mid-axillary line, and ends on the superficial surface of the serratus anterior muscle.

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Function

The long thoracic nerve is a motor nerve that provides innervation to the serratus anterior muscle. This muscle pulls the scapula anteriorly, allowing for anteversion of the arm, and elevates the ribs, assisting in respiration. The serratus anterior also assists the trapezius muscle to allow for sustained upward rotation of the scapula, which is essential for overhead lifting.

Since the long thoracic nerve is the only nerve to innervate the serratus anterior muscle, its damage causes the paralysis of this muscle, resulting in a winged scapula.