Brachial Plexus - Learning Objectives

2. Identify the scalene muscles, and describe relationships to the first rib and to neurovascular structures.

The three scalene muscles have a proximal attachment to the transverse processes of the cervical vertebrae.

They insert onto the first and second ribs:

• Anterior scalene m. – to the scalene tubercle of the 1st rib

• Middle scalene m. – to the superior surface of the 1st rib

• Posterior scalene m. – to the superior surface of the 2nd rib

Vascular relationships:

The anterior scalene muscle separates the subclavian artery and vein – the vein is anterior or superficial to the muscle at its attachment to the first rib, while the artery is deep to the muscle.

Branches of the thyrocervical trunk (from the subclavian artery) lie on the surface of the anterior anterior scalene muscle at its inferior end.  The carotid sheath, with its contents, lies vertically on the surface of the anterior scalene muscle.

Nerve relationships:

Some of the cervical nerves (VPR of C2-C8) emerge between the anterior and middle scalene muscles.  Midway down, C3, C4, and C5 emerge and contribute fibers to the phrenic nerve.  The phrenic nerve then runs longitudinally down the anterior surface of the anterior scalene muscle into the thorax. Toward the lower neck, C5-T1 emerge between the anterior and middle scalene muscles as roots of the brachial plexus.

3. Identify and list the parts and branches of the subclavian artery and vein, and describe their course in the neck.

The subclavian artery arises from the brachiocephalic trunk (right side) or the aortic arch (left side) and becomes the axillary artery distally. The subclavian artery is divided into three parts by the anterior scalene muscle.

1st part of subclavian a.: medial to the anterior scalene m. and gives off the following branches:

• • vertebral a. - travels through the foramina of the transverse processes of C1 through C6 to enter the cranial cavity through the foramen magnum.

  • internal thoracic a. – to the thorax.

  • thyrocervical trunk - four branches:

    • inferior thyroid a.

    • ascending cervical a.

    • transverse cervical a.

    • suprascapular a.

2nd part of the subclavian a.:  posterior to the anterior scalene m. and only has one branch:  

• • costocervical trunk.

3rd part of the subclavian a.: lateral to the anterior scalene m. and only has one branch:  

• • dorsal scapular a.

The subclavian a. becomes the axillary a. at the lateral (inferior) margin of the first rib.

The subclavian vein begins at the lateral border of the 1st rib and is a continuation of the axillary vein.  It unites with the internal jugular vein to form the brachiocephalic vein. This union is known as the venous angle and is the site where the thoracic duct and right lymphatic duct drain their lymph into the venous circulation. The subclavian vein also receives the external jugular vein.