Anterior Root of Fifth Thoracic Nerve (Right)

Origin

The anterior root of the fifth thoracic nerve forms from a series of rootlets that emerge from the anterolateral sulcus of the fifth thoracic spinal segment.

Course

The anterior root of the fifth thoracic nerve runs laterally and inferiorly away from the fifth thoracic spinal segment towards the intervertebral foramen located between the fifth and sixth thoracic vertebrae. Roughly within this intervertebral foramen, the anterior root merges with the posterior root to form the fifth thoracic nerve.

Branches

The anterior root of the fifth thoracic nerve merges with the posterior root to form the fifth thoracic nerve and does so without branching.

Supplied Structures & Function

The anterior root of the fifth thoracic nerve supplies all efferents for the fifth thoracic nerve, both somatic and sympathetic.

The somatic efferents pass through the spinal nerve itself and into either the posterior ramus or the anterior ramus of the fifth thoracic nerve.

—Those fibers that enter the posterior ramus convey motor innervation to the epaxial muscles, including the erector spinae (iliocostalis, longissimus, spinalis), transversospinal (rotatores, multifidus, semispinalis), and deep segmental back muscles (interspinales, levatores costarum).

—Those fibers that enter the anterior ramus of the fifth thoracic nerve (or fifth intercostal nerve) innervate the muscles of the fifth intercostal space (external intercostal, internal intercostal, innermost intercostal) and transversus thoracis muscles. A lateral branch of the intercostal nerve will innervate the serratus posterior superior muscle. Some efferents in the fifth intercostal nerve may innervate the most superior myofibers of the rectus abdominis and external abdominal oblique muscles.

Preganglionic sympathetic efferents travel from the lateral horn of the fifth thoracic spinal cord segment, through the anterior root, and into the fifth thoracic nerve. Just past the intervertebral foramen, sympathetic efferents leave the thoracic nerve via the white rami communicans to enter the sympathetic chain. The preganglionic sympathetic efferents of the fifth thoracic anterior root primarily affect sympathetic innervation of the abdomen via the greater splanchnic nerve. In particular, they target the foregut and midgut. Additionally, they control the sympathetic response in the glands and vessels of the mid-thoracic dermatomes.