longus colli muscle
The longus colli muscle is a prevertebral muscle of the neck that is innervated by the anterior rami of C2-C6 from the cervical plexus. Longus colli is a weak flexor the cervical spine and when contracting unilaterally it tilts and rotates the cervical spine to the ipsilateral side. Longus colli consists of upper (superior oblique), lower (inferior oblique) and central (vertical or intermediate) fibers.
- upper fibers: anterior tubercles of the transverse processes of C3-C5
- central fibers: anterior surface of vertebral bodies of C5-T3 vertebrae
- lower fibers: anterior surface of vertebral bodies of T1-T3 vertebrae
- upper fibers: anterior tubercle of C1 (atlas)
- central fibers: anterior surface of vertebral bodies of C2-C4 vertebrae
- lower fibers: anterior tubercles of the transverse processes of C5 and C6
- innervation: anterior rami of C2-C4 spinal nerves
- action: bilaterally longus capitis acts as a weak flexor of the head and cervical vertebrae alone unilateral action of the longus capitis muscle serves to rotate and tilt the cervical vertebrae and head to the ipsilateral side
The longus colli muscle has three distinct parts that originate from separate parts of the cervical and thoracic spine:
- superior oblique portion: originates from the anterior tubercles of the transverse processes of C3-C5 vertebrae
- vertical or intermediate part: arises from the anterior surfaces of the vertebral bodies of the C5-T3 vertebrae
- inferior oblique portion: originates from the anterior surfaces of the vertebral bodies of T1-T3 vertebrae
The longus colli muscle has separate insertion sites for the anterior oblique, intermediate and inferior oblique parts of the muscle. The superior oblique fibers insert into the tubercle of the anterior arch of the atlas. The fibers of the vertical portion of the muscle travel directly upwards to insert on to the anterior surfaces of the vertebral bodies of C2-C4. Finally, the inferior oblique part of the longus colli muscle ascends laterally attaching on to the anterior tubercles of transverse processes of C5 and C6 cervical vertebrae.
The lateral border of the inferior oblique portion of the longus colli muscle meets the medial border of the scalenus anterior (anterior scalene) to form a pyramidal space whose apex meets over the carotid tubercle (or tubercle of Chassaignac). The carotid tubercle is the anterior tubercle of the transverse process of the sixth cervical (C6) vertebra and is an important landmark in identifying the carotid artery, which sits directly anterior to it. The floor of this pyramid is formed by the first part of the subclavian artery and within this pyramidal space lies the vertebral artery and the cervical sympathetic trunk with the stellate ganglion. In dissection of the neck, it should be noted that the cervical sympathetic chain lies on the lateral aspect of the longus colli muscle at the level of C6.
The phrenic nerve arises just above the carotid tubercle and descends vertically on the scalenus anterior muscle where it is overlapped by the lateral margin of the internal jugular vein.
The longus colli muscle is innervated segmentally by anterior rami of the C2 to C6 spinal nerves from the cervical plexus.
The longus colli muscle works synergistically with longus capitis and scalene muscles as a weak flexor of the cervical spine. The action of the muscle is assisted greatly by gravity and by the powerful sternocleidomastoid muscles.