QS Study

A typical intercostal nerve is the anterior primary rami of 3rd – 6th thoracic spinal nerves, which supply only the thoracic wall, are called typical intercostal nerve. The thoracic wall is supplied by the 12 pairs of the thoracic spinal nerves.

The course of Typical Intercostal Nerve

The nerve passes through the respective intervertebral foramen and appears in the posterior part of the intercostal space, medial to the superior costotransverse ligament. It passes upwards and laterally behind the sympathetic trunk and then intervenes in the cardiothoracic fascia between costal pleura and posterior intercostal membrane. Each intercostal nerve enters the corresponding intercostal space between the posterior intercostal membrane and the parietal pleura. On reaching the angle of the upper rib, the nerve gives off a collateral and a lateral cutaneous branch, and the trunk of the nerve passes forwards along the costal groove between intercostalis internus and intimus muscles. In the costal groove, the arrangements of structures from above downwards are the vein, artery, nerve. In the anterior part of the space, the nerve passes in front of sterno-costalis muscle, crosses internal thoracic artery, pierces intercostalis intemus, anterior intercostal membrane, pectoral is major and terminates as the anterior cutaneous nerve.

Fig – Course of Typical intercostal nerve

The first six intercostal nerves give branches and terminate within their respective intercostal spaces. Seventh, eighth and ninth leave their intercostal spaces anteriorly and pass to the anterior abdominal wall. The tenth and eleventh ribs pass directly into the abdominal wall because of the fact that the corresponding ribs are floating.