Origin Transverse process of C2 to C7 Insertion Anterior and medial scalene insert on first rib. Posterior scalene inserts on second rib. Action Anterior and medial scalene elevate first rib and flexes neck to same side. Posterior scalene elevates second rib and flexes neck to same side. Innervation Brachial plexus Arterial Supply Ascending cervical a., a branch of the thyrocervical trunk