Intercostal Nerves

The intercostal nerves are the anterior rami of the first eleven thoracic spinal nerves (T1–T11). They run within the intercostal spaces between the ribs and provide motor and sensory innervation to the thoracic and upper abdominal walls. Each intercostal nerve follows a precise course within the costal groove and is accompanied by the intercostal artery and vein, forming the neurovascular bundle.

Origin

Each intercostal nerve arises from the anterior ramus of a thoracic spinal nerve (T1 to T11). These nerves exit the spinal canal via the intervertebral foramina and then enter the corresponding intercostal space.

Course

After emerging from the intervertebral foramen, each intercostal nerve travels laterally and then anteriorly within the intercostal space. It initially lies between the parietal pleura and the internal intercostal membrane, but then enters the neurovascular plane between the internal intercostal and innermost intercostal muscles. It travels in the costal groove along the inferior border of the rib, accompanied by the intercostal artery and vein (VAN: vein, artery, nerve from superior to inferior).

Branches

1. Muscular Branches

• Supply the intercostal muscles, subcostal muscles, and in the lower thoracic levels, muscles of the anterior abdominal wall such as the rectus abdominis and obliques

2. Collateral Branch

• Runs below the main nerve and assists in innervating the intercostal muscles

3. Lateral Cutaneous Branch

• Emerges at the midaxillary line and divides into anterior and posterior branches to supply the skin of the lateral thorax and abdomen

4. Anterior Cutaneous Branch

• Emerges near the sternum and supplies the skin of the anterior thoracic wall and upper abdomen

Special Cases

T1

• Most of T1 joins the brachial plexus to supply the upper limb
• A small branch continues as the first intercostal nerve

T2

• Gives rise to the intercostobrachial nerve that pierces the axilla and supplies the medial upper arm and axillary skin
• Clinically important in referred cardiac pain

T7–T11

• These continue beyond the costal margin and help innervate the anterior abdominal wall muscles and skin

Function

• Motor: Intercostal muscles, subcostal muscles, and abdominal wall muscles (T7–T11)
• Sensory: Skin of thoracic wall, anterior and lateral abdomen, and parts of the back

Dermatomes

Each intercostal nerve corresponds to a specific dermatome of the thoracic or abdominal wall:

• T2–T6: Skin of the thoracic wall
• T7–T11: Skin overlying the anterior abdominal wall
• T10: Umbilical region

Relations

• Superior: Intercostal vein and artery in costal groove
• Posterior: Pleura and thoracic vertebrae
• Anterior: Intercostal and abdominal muscles

Clinical Significance

• Intercostal neuralgia: Nerve irritation due to trauma, shingles (herpes zoster), or tumors
• Intercostal nerve block: Used for anesthesia during rib fractures or thoracic surgeries
• Referred pain: Pathology from thoracic or abdominal viscera may refer pain to these dermatomes

Topographic Summary

• Origin: Anterior rami of T1–T11 spinal nerves
• Course: Run along costal groove between internal and innermost intercostal muscles
• Function: Motor to intercostal and abdominal wall muscles; sensory to thoracic and abdominal skin
• Key branches: Collateral, lateral cutaneous, anterior cutaneous