Anterior Ramus of First Thoracic Nerve

Origin

The anterior ramus of the first thoracic nerve originates from the first thoracic nerve.

Course

The anterior ramus of the first thoracic spinal nerve originates in the neck, lateral to the intervertebral foramen between the first and second thoracic vertebrae. It runs laterally towards the space between the anterior and middle scalene muscles where it fuses with the eighth cervical root to form the inferior trunk.

Branches

The anterior ramus of the first thoracic nerve splits into two branches. The first is the small first intercostal nerve and is not part of the brachial plexus. The second and much larger branch is the inferior root of inferior trunk of the brachial plexus. Together with the eighth cervical root, it forms the inferior trunk of the brachial plexus.

Supplied Structures

The anterior ramus of the first thoracic spinal nerve carries both sensory and motor innervation.

It gives rise to a small branch that is not part of the brachial plexus. This branch, the first intercostal nerve, carries sensory fibers from the skin of the first intercostal space and motor innervation to the muscles of the first intercostal space.

The bulk of the anterior ramus of the first intercostal nerve continues laterally to become part of the first inferior trunk of the brachial plexus. This contribution carries sensory and motor innervation from the nerves distal to the inferior trunk as well as the radial nerve of the posterior cord. Broken down by nerve, the structures innervated by the anterior ramus of first thoracic nerve via the inferior trunk are:

—medial pectoral nerve supplies the pectoralis minor and pectoralis major muscles;

—medial brachial cutaneous nerve supplies skin of the medial arm;

—medial antebrachial cutaneous nerve supplies skin of the anterior and medial forearm;

—ulnar nerve supplies skin of the medial surface of the hand and all intrinsic muscles of the hand and forearm flexors not innervated by the median nerve;

—median nerve supplies skin of the lateral palmar surface of the hand and finger tips and all intrinsic muscles of the hand and forearm flexors not innervated by the ulnar nerve;

—thoracodorsal nerve supplies motor innervation of the latissimus dorsi muscle;

—radial nerve supplies sensory to skin of the posterolateral arm, posterior forearm, and posterolateral hand and motor innervation to the muscles of the posterior compartment of the arm and forearm.