Fifth Intercostal Nerve

Origin

The anterior ramus of fifth thoracic nerve (or fifth intercostal nerve) is one of two branches of the fifth thoracic nerve, the other being the posterior ramus.

Course

The anterior ramus passes forward, lying between the pleura of the lungs and the internal intercostal membranes. It then enters the space between the internal intercostal and innermost intercostal muscles to course through the fifth intercostal space. It is also accompanied by an intercostal artery and vein, where the vein sits closest to the rib above, followed by the artery and nerve. At the anterior portion of the intercostal space, the anterior ramus passes anterior to the transversus thoracis muscle and the internal thoracic vessels, where it reaches its termination as the anterior cutaneous branch.

Branches

Near its origin, the anterior ramus of the fifth thoracic nerve gives off a collateral branch that descends in the intercostal space and courses along the inferior border of the space, in the same plane as the anterior ramus itself.

The lateral cutaneous branch of the anterior ramus of fifth thoracic nerve branches from the anterior ramus around the mid-axillary line. It briefly accompanies the nerve before piercing through the chest wall. The lateral branch further subdivides into anterior and posterior branches that extend towards pectoralis major muscle and the scapula and latissimus dorsi muscles, respectively, thus, supplying the overlying skin.

The anterior cutaneous branch arises as the anterior ramus of fifth thoracic nerve reaches the anterior portion of the intercostal space. The anterior cutaneous branch also pierces the chest wall.

Supplied Structures & Function

The anterior ramus of the fifth thoracic nerve supplies motor innervation to the intercostal muscles of the fifth intercostal space (external intercostal, internal intercostal, innermost intercostal), transversus thoracis, serratus posterior superior, and the serratus anterior muscles. The anterior ramus of the fifth thoracic nerve is also the first branch of a thoracic spinal nerve to innervate the abdominal muscles, supplying motor innervation to the most superior fibers of the rectus abdominis and external oblique muscles. It also receives sensory innervation to the skin overlying the fifth intercostal space.