Medial Branches of Posterior Rami of Thoracic Nerves (Left)
Rami posteriores mediales nervorum thoracicum
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The posterior ramus of the thoracic nerve divides into medial and lateral branches lateral to the zygapophyseal joint. The medial branches continue laterally, briefly, to extend over the transverse process of the underlying vertebra. They then turn inferiorly and medially, coursing between the multifidus and semispinalis muscles.
The medial branches primarily supply motor innervation to the intrinsic muscles of the back, including multifidus, semispinalis thoracis, spinalis thoracis, interspinales thoracis, and rotatores muscles and a sensory innervation to the zygapophyseal joint via articular branches.
The upper medial branches (T1-T6) continue to travel inferomedially, piercing through the rhomboid and trapezius muscles to reach the skin, adjacent to the spinous processes of the vertebrae. The lower medial branches (T7-T12) remain intramuscular, however, occasionally supply filaments to the skin.
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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.
