The anterior vertebral muscles.
Section of the neck at about the level of the sixth cervical vertebra. Showing the arrangement of the fascia coli.
|Origin||Cervical vertebrae (CII-CVII)|
|Insertion||First and second ribs|
|Ascending cervical artery
(branch of Inferior thyroid artery)
|Cervical nerves (C3-C6)|
|Actions||Elevation of first and second ribs|
|Anatomical terms of muscle|
The scalene muscles (from Greek σκαληνός, or skalenos, meaning uneven as the pairs are all of differing length) are a group of 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).
A fourth muscle, the scalenus minimus (Sibson's muscle), is sometimes present behind the lower portion of the anterior scalene.
Origin and insertion
The scalene muscles originate from the transverse processes from the cervical vertebrae of C2 to C7 and insert onto the first and second ribs, and used to be known as the lateral vertebral muscles.
The anterior scalene muscle (or the scalenus anterior), lies deeply at the side of the neck, behind the sternocleidomastoid muscle. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and descending, almost vertically, is inserted by 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. It is supplied by the anterior ramus of cervical nerve 5 and 6.
The middle scalene, (or scalenus medius), is the largest and longest of the three scalene muscles. The middle scalene arises from the posterior tubercles of the transverse processes of the lower six cervical vertebrae. It descends along the side of the vertebral column to insert by a broad attachment into the upper surface of the first rib, between the tubercle and the subclavian groove. The brachial plexus and the subclavian artery pass anterior to it.
The posterior scalene, (or scalenus posterior) is the smallest and most deeply seated of the scalene muscles. It arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the lower two or three cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the anterior scalene. It is supplied by cervical nerves C6, C7 and C8. It is occasionally blended with the middle scalene.
The action of the anterior and middle scalene muscles is to elevate the first rib and laterally flex (bend) the neck to the same side; the action of the posterior scalene is to elevate the second rib and tilt the neck to the same side.
The scalene muscles have an important relationship to other structures in the neck. The 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 phrenic nerve is oriented vertically as it passes in front of the anterior scalene, while the subclavian vein is oriented horizontally as it passes in front of the anterior scalene muscle.
The passing of the brachial plexus and the subclavian artery through the space of the anterior and middle scalene muscles constitute the scalene hiatus (the term "scalene fissure" is also used). The region in which this lies is referred to as the scaleotracheal fossa. It is bound 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 certain forms of thoracic outlet syndrome as well as myofascial pain syndrome, the symptoms of which may mimic a spinal disc herniation of the cervical vertebrae.
Since the nerves of the brachial plexus pass through the space between the anterior and middle scalene muscles, that area is sometimes targeted with the administration of regional anesthesia by physicians. The nerve block, called an interscalene block, may be performed prior to arm or shoulder surgery.
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