Long thoracic nerve
The long thoracic nerve, also called the nerve of Bell or posterior thoracic nerve, arises just above the clavicle from the proximal portion of the brachial plexus, receiving contributions from roots of spinal nerves C5, C6 and C7.
The long thoracic nerve innervates the serratus anterior muscle, which is one of the essential muscles for moving the scapula to allow for overhead lifting of the arm. Since the long thoracic nerve provides the sole motor innervation to serratus anterior muscle, its damage can lead to the paralysis of this muscle and a phenomenon known as a winged scapula.
This article will discuss the anatomy and function of the long thoracic nerve.
|Origin||Spinal nerves C5, C6, and C7|
|Supply||Serratus anterior muscle|
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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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.
Long thoracic nerve injury
The long thoracic nerve is susceptible to damage due to its long and relatively superficial course. Damage to this nerve can occur during certain surgical procedures in the thoracic region, such as radical mastectomy and chest tube placements, or through direct trauma or stretch. There are also reports of non-traumatic causes of long thoracic nerve damage, such as viral infections, poliomyelitis and allergic drug reactions.
The injury of the long thoracic nerve can cause a phenomenon known as winging of the scapula. Upon physical examination, the scapular winging is usually evident at rest, but it can also be accentuated when the arm is elevated anteriorly, or when pushing the outstretched arm against a wall.
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