Quick Facts
Origin: In or just lateral to the intervertebral foramen between the T1 and T2 vertebrae.
Course: Laterally a short distance to the bifurcation of anterior and posterior rami.
Branches: Anterior and posterior rami.
Supply: The posterior ramus supplies motor innervation to the epaxial muscles. It conveys sensory innervation from the skin over the upper dorsal trunk and upper limb. The anterior ramus supplies motor innervation to the muscles of the first intercostal space via the first intercostal nerve and muscles of the forearm and hand via the brachial plexus. It conveys sensory innervation from the skin of the anterolateral thoracic wall and medial surfaces of the arm and forearm.
Related parts of the anatomy
Origin
The first thoracic nerve is formed when the posterior and anterior roots of the first thoracic nerve merge, roughly in the intervertebral foramen between the T1 and T2 vertebrae.
Course
The first thoracic nerve runs only a very short distance laterally, from its origin at the merger of posterior and anterior roots, to its bifurcation into posterior and anterior rami. This all occurs in or lateral to the intervertebral foramen between the T1 and T2 vertebrae.
Branches
The first thoracic nerve gives rise to two branches or rami: the anterior and posterior rami. The anterior and posterior rami carry all somatic motor and sensory innervation from the first thoracic spinal level as well as the sympathetic fibers associated with tissue targeted by this nerve.
The posterior ramus runs posteriorly to the epaxial musculature overlying the T1-T2 vertebrae, where it gives off both lateral and medial branches.
The anterior ramus forms two nerves. The bulkier nerve forms the inferior root of inferior trunk of the branchial plexus. It runs laterally out of the thorax to merge with fibers of the eighth cervical anterior ramus, thus forming the inferior trunk of the brachial plexus. These fibers contribute to the median, radial, ulnar, and medial pectoral nerves, as well as the medial brachial and antebrachial cutaneous nerves.
The smaller branch of the anterior ramus forms the first intercostal nerve, which remains in the first intercostal space. It courses between the internal intercostal and the innermost intercostal muscles.
Supplied Structures & Function
The first thoracic spinal nerve splits into two branches: the posterior and anterior rami.
The posterior ramus conveys motor innervation to the epaxial muscles epaxial muscle, including the erector spinae (iliocostalis, longissimus, spinalis), transversospinal (rotatores, multifidus, semispinalis), and deep segmental back muscles (interspinales, levatores costarum). The posterior ramus conveys sensory innervation from the skin of the back. See dermatome map for cutaneous distribution.
The first intercostal nerve, which arises from the anterior ramus, supplies the intercostal muscles of the first intercostal space (external intercostal, internal intercostal, innermost intercostal), and the skin of the anterolateral thoracic wall.
The larger inferior root of the inferior trunk of the branchial plexus, which arises from the anterior ramus of first thoracic nerve contributes both motor and sensory innervation to the upper limb.
List of Clinical Correlates
—Horner’s syndrome
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Thoracic Nerves
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.
