Anterior Root of Sixth Thoracic Nerve (Right)

Origin

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

Course

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

Branches

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

Supplied Structures & Function

The anterior root of the sixth thoracic nerve supplies all efferents for the sixth 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 sixth 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 sixth thoracic nerve (or sixth intercostal nerve) innervate the muscles of the sixth intercostal space (external intercostal, internal intercostal, innermost intercostal) and transversus thoracis muscles. Some efferents in the sixth intercostal nerve may also innervate the most superior myofibers of the rectus abdominis and external abdominal oblique muscles.

Preganglionic sympathetic efferents travel from the lateral horn of the sixth thoracic spinal cord segment, through the anterior root, and into the sixth 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 sixth 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.