Scalene Muscles

• There are usually three scalene muscles, the scalenus anterior, the scalenus medius and the scalenus posterior. 
• The scalenus medius is the largest, and the scalenus posterior the smallest, of three. 
• These muscles extend from the transverse processes of cervical vertebrae to the first two ribs. 
• They can, therefore, either elevate these ribs or bend the cervical part of the vertebral column laterally

Scalenus anterior

Origin 

Anterior tubercles of transverse processesof cervical vertebrae 3, 4, 5 and 6

Insertion

Scalene tubercle and adjoining ridge on the superior surface of the first rib (between subclavian artery and 

vein)

Nerve Supply

Ventral rami of nerves C4-C6

Action

a. Anterolateral flexion of cervical spine

b. Rotates cervical spine to opposite side

c. Elevates the first rib during inspiration

d. Stabilises the neck along with other muscles

Relations of scalenus anterior. 

The scalenus anterior is a key muscle of the lower part of the neck because of its intimate relations to many important structures in this region. It is a useful surgical landmark.

Anterior:

a. Phrenic nerve covered by prevertebral fascia.

b. Lateral part of carotid sheath containing the internal jugular vein.

c. Sternocleidomastoid.

d. Clavicle.

Posterior:

a. Brachial plexus.

b. Subclavian artery.

c. Scalenus medius.

d. Cervical pleura covered by the suprapleural membrane

The medial border of the muscle is related:

a. In its lower part to an inverted ‘V'-shaped interval, formed by the diverging borders of the scalenus anterior and the longus colli. 

This interval contains many important structures as follows:

i. Vertebral vessels running vertically from the base to the apex of this space.

ii. Inferior thyroid artery arching medially at the level of the 6th cervical transverse process.

iii. Sympathetic trunk.

iv. The first part of the subclavian artery traverses the lower part of the gap.

v. On the left side, the thoracic duct arches laterally at the level of the seventh cervical transverse process

vi. The carotid sheath covers all the structures mentioned above.

vii. The sternocleidomastoid covers the carotid sheath.

b. In its upper part, the scalenus anterior is separated from the longus capitis by the ascending cervical artery.

The lateral border of the muscle is related to the trunks of the brachial plexus and the subclavian artery which emerges at this border and enter the posterior triangle

Scalenus medius

Origin

a. Posterior tubercles of transverse processes of cervical vertebrae 3, 4, 5, 6,7

b. Transverse process of axis and sometimes also of the atlas vertebra

Insertion

Superior surface of the first rib behind the groove for the subclavian artery

Nerve Supply

Ventral rami of nerves C3-C8

Action

a. Lateral flexion of the cervical spine.

b. Elevation of first rib

c. Stabilises neck along with other muscles

Scalenus posterior

Origin

Posterior tubercles of transverse processes of cervical vertebrae 4,5,6

Insertion

Outer surface of the second rib behind the tubercle for the serratus anterior

Nerve Supply

Ventral rami of nerves C6-C8

Action

Lateral flexion of cervical spine

Elevation of the second rib

Stabilises neck along with other muscles

Sometimes a fourth, rudimentary scalene muscle, the scalenus minimus is present. 

Origin 

from the anterior border of the transverse process of vertebra C7 and

Insertion 

the inner border of the first rib behind the groove for the subclavian artery and into the dome of the cervical pleura. 

The suprapleural membrane is regarded as the expansion this muscle.

Contraction of the scalenus minimus pulls the dome of the cervical pleura

Watch lectures on YouTube:

Paravertebral Muscles - The Scalenus Anterior muscle| Attachments | Nerve supply| Action | Relations

Para-vertebral muscles - Scalenii medius, posterior & minimus muscles | Attachments | Morphology |