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The scalene muscles are three pairs of muscles in the lateral neck, namely the anterior scalene, middle scalene, and posterior scalene.
They are innervated by the fourth, fifth, and sixth cervical spinal nerves (C4-C6).
The anterior and middle scalene muscles lift the first rib and bend the neck to the same side.
The posterior scalene lifts the second rib and tilts the neck to the same side.
The scalene muscles originate from the transverse processes from the cervical vertebrae of C2 to C7.
The scalene muscles insert onto the first and second ribs.
The anterior scalene muscle lies deep into the side of the neck, behind the sternocleidomastoid muscle.
The anterior scalene muscle arises from the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae.
The anterior scalene muscle descends almost vertically, inserting as a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the second rib in front of the subclavian groove.
The anterior scalene muscle is supplied by the anterior ramus of cervical nerve 5 and 6.
The middle scalene muscle is the largest and longest of the three scalene muscles, and it arises from the transverse processes of the lower six cervical vertebrae.
It descends along the side of the vertebral column to insert into the upper surface of the first rib.
The brachial plexus and the subclavian artery pass anterior to it.
The posterior scalene muscle is the smallest and most deeply seated of the scalene muscles.
It arises from two or three separate tendons, from the transverse processes of the lower two or three cervical vertebrae, and is inserted into the outer surface of the second rib, behind the attachment of the anterior scalene.
The posterior scalene muscle is supplied by cervical nerves C5, C6 and C7.
The scalenus minimus muscle is sometimes present behind the lower portion of the anterior scalene.
The anterior and middle scalene muscles lift the first rib and bend the neck to the same side as the acting muscle.
Similarly, the posterior scalene lifts the second rib and tilts the neck to the same side.
The scalene muscles elevate the upper ribs, acting as accessory muscles of respiration, with the sternocleidomastoids.
Anatomically the scalene muscles have an important relationship to other structures in the neck:
brachial plexus and subclavian artery pass between the anterior and middle scalenes;
the subclavian vein and phrenic nerve pass anteriorly to the anterior scalene as the muscle crosses over the first rib.
The brachial plexus and the subclavian artery pass through the space of the anterior and middle scalene muscles constitute the scalene hiatus.
The scaleotracheal fossa is bounded by the clavicle inferior anteriorly, the trachea medially, posteriorly by the trapezius, and anteriorly by the platysma muscle.
The anterior and middle scalene muscles can be involved in a thoracic outlet syndrome.
The anterior and middle scalene muscles may be related to a myofascial pain mimicking a spinal disc herniation of the cervical vertebrae.
The brachial plexus passes through the space between the anterior and middle scalene muscles, and is the target for with the administration of regional anesthesia nerve block, called an interscalene block.