Anterior Root of Eleventh Thoracic Nerve (Right)

Origin

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

Course

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

Branches

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

Supplied Structures & Function

The anterior root of the eleventh thoracic nerve supplies all efferents for the eleventh 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 eleventh 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 eleventh thoracic nerve (or eleventh intercostal nerve) innervate the muscles of the eleventh intercostal space (external intercostal, internal intercostal, innermost intercostal) and the subcostal muscles. A lateral branch of the intercostal nerve will innervate the serratus posterior inferior muscle. Additionally, efferents in the eleventh intercostal nerve continue anteriorly to innervate most of the abdominal muscles (rectus abdominis, external abdominal oblique, internal abdominal oblique, and transversus abdominis).

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