Shoulder & Brachial Plexus LO7
7. 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
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.
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.