Quick Facts
Origin: Anterior tubercles of transverse processes of C3-C6 vertebrae.
Insertion: Scalene tubercle of first rib.
Action: Flexes, rotates, and laterally flexes neck; elevates first rib.
Innervation: Anterior rami of fourth to sixth cervical nerves (C4-C6).
Arterial Supply: Ascending cervical artery.
Related parts of the anatomy
Origin
The scalenus anterior muscle arises from the anterior tubercles of the transverse processes of the third to sixth cervical vertebrae (C3-C6).
Insertion
The fibers of the scalenus anterior muscle descend and attach to the scalene tubercle of the first rib.
Key Features & Anatomical Relations
The scalenus anterior muscle is an important landmark of the neck. Anteriorly, it has anatomical related to the following structures.
- The phrenic nerve descends on the anterior aspect of the scalenus anterior muscle. It is covered in prevertebral fascia, which keeps the nerve and muscle together along its descent.
- Branches of the thyrocervical trunk lie medial or anterior to the scalenus anterior muscle. These vessels include the ascending cervical branch of the inferior thyroid artery.
- Inferiorly, the subclavian vein sits in the groove on the first rib in front of the scalenus anterior muscle.
- Other structures that lie anterior to the scalenus anterior muscle include the sternocleidomastoid and omohyoid muscles.
Inferomedially, the scalenus anterior muscle is separated from the longus colli muscle by a triangular space, sometimes referred to as the pyramidal space (Sinnatamby, 2011). It is within this space that the vertebral artery and vein gains access to the transverse foramen of sixth cervical vertebra (C6). The cervical ganglion of the sympathetic trunk is situated deep in this space. The inferior thyroid artery crosses this space to provide vascular supply to the thyroid. The thoracic duct also crosses this space on the left-hand side.
Unlike the subclavian veins, the second part of the subclavian artery lies deep to the scalenus anterior muscle as it courses laterally towards the axilla.
On the lateral aspect of the scalenus anterior muscle, the brachial plexus and the third portion of the subclavian artery emerge as they travel to the upper limb.
Actions
The scalenus anterior muscle is involved in multiple actions:
- during bilateral contraction, it flexes the neck at the cervical vertebral joints;
- during unilateral contraction, it rotates the neck to the opposite side at the cervical vertebral joints;
- during unilateral contraction, it laterally flexes the neck to the same side at the cervical vertebral joints;
- it elevates the first rib and can act as an accessory muscle of inspiration (Standring, 2016).
References
Sinnatamby, C. S. (2011) Last's Anatomy: Regional and Applied. ClinicalKey 2012: Churchill Livingstone/Elsevier.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.
