Scalenus anterior muscle

At a glance

English

Scalenus anterior muscle

Latin (TA2)

Musculus scalenus anterior

System

Muscle

Region

Neck

Side

Paired, left and right

Inserts on

The vertebra c5 and vertebra c6

About the scalenus anterior muscle

Scalenus anterior is one of the scalene muscles, the group in the lateral neck that joins the cervical spine to the upper ribs; the middle and posterior scalenes are its partners. Their name comes from the Greek word for uneven, because they differ in length. Scalenus anterior lies deep in the lateral neck, under cover of sternocleidomastoid, and is one of the most important landmarks of the root of the neck.

It arises by small tendons from the front tubercles of the C3 to C6 transverse processes. The slips join and the muscle runs downwards and slightly forwards, almost vertically, to end by a narrow, flat tendon on the scalene tubercle, a mark on the first rib's inner edge, and on the ridge just in front of the rib's groove for the subclavian artery. A small extra muscle, scalenus minimus, sometimes lies behind its lower part.

With the neck fixed, it raises the first rib, so it acts as an accessory muscle of breathing, used during heavy or laboured inspiration along with sternocleidomastoid. With the rib fixed, it bends the neck forwards and to the same side and turns it slightly to the opposite side. It is supplied by ventral rami of C4 to C6, and its blood comes mainly from the ascending cervical branch of the inferior thyroid artery.

Its relations explain its clinical importance. The phrenic nerve runs vertically down its front surface, and the subclavian vein crosses horizontally in front of its lower end. Behind it, in the gap between it and scalenus medius, run the subclavian artery and the roots and trunks of the brachial plexus. Tight scalenes or an extra cervical rib can squeeze these in thoracic outlet syndrome, and muscle pain here can mimic a cervical disc problem. Anaesthetists inject local anaesthetic into this gap to numb the arm before shoulder surgery, a technique known as an interscalene block.

Attachments, action and supply

Origin

Front tubercles of the C3 to C6 transverse processes.

Insertion

Scalene tubercle on the first rib's inner edge and the ridge just ahead of the rib's subclavian groove.

Action

Raises the first rib in forced breathing; bends the neck forwards and to the same side.

Nerve supply

Ventral rami of C4 to C6.

Blood supply

Ascending cervical branch of the inferior thyroid artery.