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Anterior Root of Fourth Thoracic Nerve (Left)
Nervous System

Anterior Root of Fourth Thoracic Nerve (Left)

Radix anterior nervi thoracici quarti

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Quick Facts

Origin: Anterolateral sulcus of spinal cord.

Course: Laterally towards intervertebral foramen.

Branches: None.

Supply: Motor innervation to epaxial muscles of mid trunk, intercostal muscles of fourth intercostal space. Sympathetic targets in the thorax and territories of fourth thoracic nerve.

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Origin

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

Course

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

Branches

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

Supplied Structures & Function

The anterior root of the fourth thoracic nerve supplies all efferents for the fourth 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 fourth 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 fourth thoracic nerve (or fourth intercostal nerve) innervate the muscles of the fourth intercostal space (external intercostal, internal intercostal, innermost intercostal) and transversus thoracis muscle. A lateral branch of the intercostal nerve will innervate the serratus posterior superior muscle.

Preganglionic sympathetic efferents travel from the lateral horn of the fourth thoracic spinal cord segment, through the anterior root, and into the fourth 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 fourth thoracic anterior root primarily affect sympathetic innervation of thoracic organs, such as the lungs and heart. Additionally, they control the sympathetic response in the glands and vessels of the upper to mid thoracic dermatomes.

Learn more about this topic from other Elsevier products

Thoracic Nerves

ScienceDirect image

The 12th thoracic nerve is called the subcostal nerve and is unique in that it gives off a branch to the first lumbar nerve, thus contributing to the lumbar plexus.

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Complete Anatomy

The world's most advanced 3D anatomy platform

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