Origin: Ventral branches of thoracic spinal nerves (T1-T13).

Course:
- Run in the costal groove (caudal border of rib).
- Order in the groove: V-A-N (Vein on top, Artery middle, Nerve below) — top to bottom.

Supply:
- Motor: External & internal intercostal muscles, transversus thoracis, abdominal muscles (last 2 nerves).
- Sensory: Skin and parietal pleura of the lateral chest wall.

Clinical: Site for Intercostal Nerve Block = caudal border of rib, near vertebral end (paravertebral approach).

NERVES OF THE CHEST WALL — INTERCOSTAL NERVES

These are the ventral (forward) branches of the thoracic spinal nerves T1-T13. Each thoracic spinal nerve, after leaving the spine, divides into a small dorsal branch (to back muscles & skin) and a larger ventral branch — and the ventral branch is the intercostal nerve.

COURSE: Each intercostal nerve runs along the caudal (back) border of its own rib, in the groove formed there (costal groove). It is accompanied by the intercostal artery and vein. The order from top to bottom (or rather from above downward in the groove) is:
V — A — N (Vein, Artery, Nerve)
This order is essential to remember when placing a needle: you put the needle along the cranial border of the rib to AVOID this bundle.

BRANCHES:
• Lateral cutaneous branch — pierces muscle to supply skin on the side of the chest.
• Ventral cutaneous branch — supplies skin near the sternum.
• Muscular branches — to external/internal intercostals, transversus thoracis.
• The last 2-3 intercostal nerves leave the chest and run on to supply the muscles and skin of the abdomen.

CLINICAL — INTERCOSTAL NERVE BLOCK:
Useful for pain after rib fracture, thoracotomy or for paracentesis. Local anaesthetic is deposited along the caudal border of the rib, close to the spine, blocking that nerve's whole field.