QS Study

Typical intercostal nerve

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. Anterior and posterior rami are formed as soon as they leave the intervertebral foramina.


It is formed by ventral and dorsal roots of spinal nerves. They may be segmental in nature unlike the anterior primary rami from some other regions of the spinal cord which create nerve plexuses viz. cervical, brachial, lumbar and sacral.

Fig – Formation of a typical thoracic spinal nerve

The intercostal nerves are classified into the following 2 groups:

Typical intercostal nerves (3rd, 4th, 5th, and 6th).

Atypical intercostal nerves (1st, 2nd, 7th, 8th, 9th, 10th, and 11th).


(i) Small muscular branches to the intercostal, transverses thoracic group and serratus posterior superior muscles.

(ii) Collateral branches that supply the muscles of that space, parietal pleura and periosteum of the rib. It runs parallel to the main nerve on the upper border of the rib below.

(iii) Cutaneous branches:

  1. Lateral cutaneous &
  2. Anterior cutaneous branches.

(iv) Communicating branches:

  1. Gray rami communicants &
  2. White rami communicants.
  3. Anterior part of the space, the nerves communicate with adjacent intercostal nerves, behind the costal cartilage.