Thursday, December 1, 2011

Thoracic Spinal Nerves

There are twelve thoracic spinal nerves, each of them dividing into a posterior branch and an anterior branch. Each posterior branch divides into a medial and a lateral branch; both supply motor fibers to the deep autochthonous back muscles. Sensory innervation of the back comes mainly from the lateral branches of the posterior branches. The anterior branches of the spinal thoracic nerves run as intercostal nerves between the ribs, initially on the inner surface of the thorax and later within the internal intercostal muscles. An upper group and a lower group of intercostal nerves can be distinguished: the nerves of the upper group (T1–T6) run up to the sternum and supply the intercostal muscles, the superior and inferior posterior serrate muscles, and the transverse thoracic muscle, giving off sensory branches to the skin of the thorax; the nerves of the lower group (T7–T12), the intercostal segments of which no longer end at the sternum, extend across the costal cartilages up to the white line, taking an increasingly oblique downward path and supplying the muscles of the abdominal wall (abdominal transverse muscle, external and internal abdominal oblique muscles, rectus abdominis muscle and pyramidal muscle).