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Thoracic Nerves

Nervi thoracici

For medical students2 min readUpdated 2026-10-10

The thoracic nerves are twelve pairs of spinal nerves that innervate the walls of the thorax and abdomen. Unlike most other spinal nerves, they maintain a clear segmental arrangement and generally do not form nerve plexuses.

Quantity12 pairs (Th₁–Th₁₂)
TypeMixed (containing motor and sensory fibers)
PlexusesNone formed (except for a contribution from Th₁ to the brachial plexus)

General Characteristics and Primary Branches

The thoracic nerves (nervi thoracici) are represented by 12 pairs of spinal nerves, designated from Th₁ to Th₁₂. One of their main features is the absence of nerve plexus formation: each nerve travels in an isolated manner. The only exception is the first thoracic nerve (Th₁), which partially contributes to the formation of the brachial plexus (plexus brachialis).

In composition, every thoracic nerve is mixed. Upon exiting the vertebral canal through the intervertebral foramen, the nerve trunk immediately divides into several branches:

Dorsal Rami of Thoracic Nerves

The dorsal rami (rr. dorsales nn. thoracicorum) retain a mixed character, carrying both motor and sensory nerve fibers.

Topographically, each dorsal ramus passes to the posterior aspect of the trunk, where it invariably divides into two branches:

  1. Medial branch (r. medialis);
  2. Lateral branch (r. lateralis).

Anterior Rami: Intercostal and Subcostal Nerves

The anterior rami of the thoracic nerves (rr. anteriores nn. thoracicorum) show significant topographical differences depending on their level of origin.

Intercostal Nerves (nn. intercostales) The anterior rami of the first through eleventh pairs (Th₁–Th₁₁) are termed the intercostal nerves. They lie strictly within their corresponding intercostal spaces. Each such nerve runs between the internal intercostal muscle (m. intercostalis internus) and the innermost intercostal muscle (m. intercostalis intimus). The intercostal nerve always accompanies matching blood vessels, forming the intercostal neurovascular bundle.

Subcostal Nerve (n. subcostalis) The anterior ramus of the twelfth thoracic nerve (Th₁₂) is called the subcostal nerve. Unlike the others, it lies outside an intercostal space — its trunk passes inferior to the 12th rib. The subcostal nerve participates in the innervation of the anterior abdominal wall muscles, gives off cutaneous branches to the lumbar region and lower abdomen, and contributes to the formation of the lumbar plexus.

Cutaneous Branches of the Anterior Trunks

To provide sensation to the skin of the thorax and abdomen, the intercostal nerves give off specialized cutaneous branches divided into two major groups.

Lateral Cutaneous Branches (rr. cutanei laterales) These branches pierce the muscles and emerge into the subcutaneous tissue along the midaxillary line. Each lateral branch divides into an anterior and a posterior branch. They innervate the skin of the lateral chest and abdominal wall. Notable lateral branches:

Anterior Cutaneous Branches (rr. cutanei anteriores) These are the terminal branches of the intercostal nerves. They emerge into the subcutaneous tissue along the parasternal line and similarly divide into medial and lateral branches, supplying sensation to the skin of the anterior chest and abdominal wall. Notable anterior branches:

Mnemonic

To remember the arrangement of the intercostal neurovascular bundle (from superior to inferior), use the mnemonic "VAN": Vein – Artery – Nerve. The nerve is always located inferior to the vessels, which is critical to remember when performing a thoracentesis or pleural tap.

Frequently asked questions

Which specific muscles are innervated by the dorsal rami of the thoracic nerves?

The dorsal rami of the thoracic nerves innervate the deep muscles of the back, also known as the intrinsic back muscles. The dorsal ramus of each thoracic nerve divides into a medial branch (r. medialis) and a lateral branch (r. lateralis). These rami carry both motor and sensory fibers to supply the deep back muscles and overlying skin.

Which specific muscles of the anterior abdominal wall are innervated by the subcostal nerve?

The subcostal nerve (n. subcostalis, Th₁₂) participates in the innervation of the abdominal wall muscles. It runs across the quadratus lumborum muscle and terminates in the inferior part of the rectus abdominis muscle and the pyramidalis muscle.

In what order (from superior to inferior) are the elements of the neurovascular bundle arranged in the intercostal space?

In the intercostal space, the elements of the neurovascular bundle are arranged in the order designated by the abbreviation V–A–N (Vein, Artery, Nerve).

The bundle lies within the costal groove (sulcus costae) along the inferior margin of each rib. It runs between the internal intercostal muscles (mm. intercostales interni) and the innermost intercostal muscles (mm. intercostales intimi). Anterior to the midaxillary line, the vessels and nerves are no longer protected by the ribs and enter the intermuscular tissue plane.

Which thoracic wall muscles are innervated by the muscular branches of the intercostal nerves?

The muscular branches of the intercostal nerves (rr. musculares) innervate all ventral muscles of the thoracic wall, as well as muscles of ventral origin located on the back.

These include the following muscles:

  • External intercostal muscles (mm. intercostales externi) — ventral thoracic wall muscles
  • Internal intercostal muscles (mm. intercostales interni) — ventral thoracic wall muscles
  • Innermost intercostal muscles (mm. intercostales intimi) — ventral thoracic wall muscles
  • Subcostal muscles (mm. subcostales) — ventral thoracic wall muscles
  • Transversus thoracis muscle (m. transversus thoracis) — ventral thoracic wall muscles
  • Serratus posterior superior and inferior muscles (mm. serrati posteriores superior et inferior) — back muscles of ventral origin
  • Levatores costarum muscles (mm. levatores costarum) — back muscles of ventral origin
Do thoracic nerves participate in the formation of nerve plexuses?

Generally no, they maintain a strict segmental arrangement. The only exceptions are the first thoracic nerve (Th₁), fibers of which contribute to the brachial plexus, and the subcostal nerve (Th₁₂), which participates in forming the lumbar plexus.

Between which muscles does the trunk of the intercostal nerve run?

Each intercostal nerve travels between the internal intercostal muscle (m. intercostalis internus) and the innermost intercostal muscle (m. intercostalis intimus).

How does the topography of the subcostal nerve (Th₁₂) differ?

Unlike the other anterior rami, it does not run within an intercostal space; instead, it lies inferior to the 12th rib as it courses toward the muscles and skin of the abdominal wall.

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