Scaleni

Scaleni, or scalene muscles, are a group of three paired muscles in the lateral aspect of the neck: the anterior scalene (musculus scalenus anterior), the middle scalene (musculus scalenus medius), and the posterior scalene (musculus scalenus posterior). They form part of the lateral cervical wall and lie anterior to the lower part of the neck’s neurovascular trunk. In common descriptions, the anterior and middle scalene originate from the transverse processes of cervical vertebrae and insert on the first rib, while the posterior scalene originates from lower cervical transverse processes and inserts on the second rib. There is some anatomical variation in exact origins, but the general pattern is consistent.

Nerve supply to the scalene muscles comes from branches of the ventral rami of cervical nerves, typically from C4 to C8, reflecting their role in the neck’s motor innervation.

Functions of the scalene muscles include elevating the first and, to a lesser extent, the second rib during forced inspiration, contributing to respiration. They also assist in lateral flexion of the neck and, for some fibers, flexion of the neck. Because of their location, the scalene muscles are involved in several clinical considerations, including thoracic outlet syndrome when the brachial plexus or subclavian vessels are compressed between the scalene muscles, particularly the anterior and middle scalene.

Relation to other structures is clinically relevant: the brachial plexus trunks pass between the anterior and middle scalene muscles, the subclavian artery lies between these two muscles, and the subclavian vein is anterior to the anterior scalene.

Etymology-wise, the term scalene derives from Latin scaleneus, meaning uneven or oblique, describing their slanted orientation.