Hey everybody! It’s Matt from Kenhub, and in this tutorial, we will be discussing the scalene muscles. The name scalene comes from the Latin word scala meaning ladder. The scalene muscles are three paired cervical muscles running from the cervical vertebrae to the upper two ribs. They form a roof over the pleura and the upper thorax. The innervation of all three scalene muscles is carried by direct branches of the cervical and brachial plexuses.
As I mentioned at the beginning of this tutorial, the scalene muscles are comprised of three pairs of muscles namely anterior scalene, middle scalene and the posterior scalene. The anterior scalene muscle runs from the anterior tubercles of the transverse processes of C3 to C6 – i.e. the third to sixth cervical vertebrae – and has its insertion on the scalene tubercle of the first rib.
The middle scalene muscle originates at the posterior tubercles of the transverse processes of C3 to C7 – i.e. the third to seventh cervical vertebrae – and has its insertion at the first rib behind the groove for the subclavian artery. It is situated dorsally to the anterior scalene muscle. The posterior scalene muscle has its origin at the posterior tubercles of the transverse processes of C5 to C7 – i.e. the fifth to seventh cervical vertebrae – and its insertion at the upper margin of the second rib.
The triangle between the anterior scalene, the middle scalene and the first rib form the interscalene triangle. The subclavian artery – highlighted in this image in green – and the brachial plexus pass through this gap. But note this, the subclavian vein runs ventrally from the anterior scalene muscle.
The scalene muscles elevate the ribs and, therefore, the thorax. For that reason, they are also considered as accessory muscles of inspiration. A unilateral contraction bends the cervical spine to the side known as lateral flexion. Furthermore, a bilateral contraction of the anterior scalene muscle causes bending of the cervical spine to the front known as ventral flexion.
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