Nerves of Thorax

Major nerves supplying the Thorax are:

• Intercostal Nerves
• Spinal Nerves
• Vagus Nerve
• Phrenic Nerve
• Sympathetic Chain

Intercostal Nerves

Intercostal nerves is the name given to the anterior primary rami of the upper 11 thoracic spinal nerves (T1 T11) as they use the route through the intercostal spaces. The thoracic wall is supplied by the 12 pairs of the thoracic spinal nerves. Anterior and posterior rami are formed as soon as they leave the intervertebral foramina.

The abdominal wall below the 12th rib is where the anterior primary ramus of the 12th thoracic nerve runs and this is why it is termed as subcostal nerve.

The intercostal nerves are anterior primary rami of thoracic spinal nerves. They may be segmental in nature unlike the anterior primary rami from some other regions of spinal cord which create nerve plexuses viz. cervical, brachial, lumbar and sacral.

Spinal Nerves

A spinal nerve is composed of many nerves, which carries motor, sensory, and autonomic signals between the spinal cord and the body. Human body consist of 31 pairs of spinal nerves, one on each side of the vertebral column.

The 31 sets of spinal nerves are segmental in circulation and arise via the vertebral canal in between the stalks of surrounding vertebrae. There are:

• 8 sets of cervical nerves (Cl to C8)
• 12 thoracic (T1 to T12)
• 5 lumbar (LI to L5)
• 5 sacral (SI to S5)
• 1 coccygeal (Co)

Vagus Nerve

It’s a mixed nerve, i.e., composed of both the motor and sensory fibres but mostly it is motor. Vagus nerve is the 10th cranial nerve. Its area of distribution goes past the head and neck-to the thorax and abdomen. It’s the longest and most widely distributed cranial nerve. It’s so called due to its wide-ranging obscure course and distribution. It’s a vagrant or wandering nerve. It spreads the fibres of a cranial part of the accessory nerve and carries majority of the efferent fibres of the cranial part of the parasympathetic outflow.

The vagus nerve originates from the lateral aspect of the medulla between the olive and inferior cerebellar peduncle by about 10 rootlets below and in line of the rootlets of the glossopharyngeal nerve. These nerve rootlets unify to create the nerve trunk which runs laterally, crosses the jugular tubercle and leaves the cranial cavity by going through the middle part of the jugular foramen enclosed in the common dural sheath with the 11th nerve.

Phrenic Nerve

The point of origin of Phrenic nerve is from ventral rami of C3, C4 and C5 but primarily from C4. Phrenic nerve runs vertically downwards on the anterior surface of the scalenus anterior, which it crosses obliquely from lateral to medial side. Afterward it runs downwards on the cervical pleura to go into the thorax behind first costal cartilage.

The phrenic nerve gives:

• Single Motor Supply to the diaphragm (muscle of respiration).
• Sensory innervation to diaphragmatic pleura, pericardium and subdiaphragmatic pleura.

Sympathetic Chain

Thoracic Sympathetic Trunk is a ganglionated chain, situated on each side of the vertebral column. In the thoracic inlet, it’s superiorly continuous with the cervical sympathetic chain and with the lumbar sympathetic chain inferiorly after passing behind the medial arcuate ligament of the diaphragm.

The sympathetic chain descends in front of the neck of the 1st rib, head of 2nd-10th ribs and along the bodies of T11 and T12 vertebrae, in front of posterior intercostal nerve and vessels, enters behind the medial arcuate ligament to become continuous with the lumbar sympathetic trunk.