Medial Branches of Posterior Rami of Thoracic Nerves (Left)

Description

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.