Longissimus

The longissimus (Latin: musculus longissimus) is a deep muscle of the back that participates in the formation of the erector spinae muscle complex along with the iliocostalis and spinalis muscles. Erector spinae muscles lie in the intermediate layer of the deep back muscles.

The longissimus is the most central erector spinae muscle, and it is also the longest and thickest of all three. The longissimus is composed of three parts based on their location and superior attachments, and they are named after their location - longissimus capitis, longissimus cervicis and longissimus thoracis.

Longissimus capitis

The longissimus capitis (Latin: musculus longissimus capitis) is a portion of the longissimus muscle complex that is located in the neck. It is the most cranially located longissimus muscle, and it lies medial to the longissimus cervicis.

Origin

The longissimus capitis muscle originates from the transverse processes of the lower three or four cervical vertebrae (C4/C5 - C7) and upper five thoracic vertebrae (T1 - T5).

Insertion

The fibers of the longissimus capitis insert on the mastoid process of the temporal bone of the skull.

Action

Muscle contractions on both sides (bilateral contractions) extend the head and neck. Contractions on one side (unilateral contractions) provide lateral flexion and rotation of the head to the same side (ipsilateral).

Innervation

The longissimus capitis is innervated by the lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply

The blood supply to the longissimus capitis muscle is provided by the branches of the occipital, vertebral, deep cervical and transverse cervical arteries. The occipital artery is a branch of the external carotid artery, while the vertebral artery arises from the subclavian artery. The deep cervical artery branches off the costocervical trunk, and the transverse cervical artery originates from the thyrocervical trunk.

Longissimus cervicis

The longissimus cervicis (Latin: musculus longissimus cervicis; musculus longissimus colli) is the middle portion of the longissimus muscle complex, and it is located in the neck. The longissimus cervicis lies medial to the longissimus thoracis.

Origin

The longissimus cervicis originates from the transverse processes of the upper four to five thoracic vertebrae (T1 - T4/T5).

Insertion

The fibers of the longissimus cervicis insert on the posterior tubercles of the transverse processes of the second to sixth cervical vertebrae (C2 - C6).

Action

Muscle contractions on both sides (bilateral contractions) extend the cervical and thoracic spine. Contractions on one side (unilateral contractions) provide lateral flexion of the cervical and thoracic spine to the same side (ipsilateral).

Innervation

The longissimus cervicis is innervated by the lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply

The blood supply to the longissimus cervicis muscle is provided by the branches of the occipital, vertebral, deep cervical and transverse cervical arteries. The occipital artery is a branch of the external carotid artery, while the vertebral artery arises from the subclavian artery. The deep cervical artery branches off the costocervical trunk, and the transverse cervical artery originates from the thyrocervical trunk.

Longissimus thoracis

The longissimus thoracis (Latin: musculus longissimus thoracis) is the most lowest portion of the longissimus muscle. At the same time, it is the most significant muscle of the longissimus muscle complex. The longissimus thoracis is composed of two parts - thoracic and lumbar.

Origin

The thoracic part of the longissimus thoracis arises from the spinous and transverse processes of the first to fifth lumbar vertebrae (L1 - L5), median sacral crest, dorsal surface of the sacrum and posterior aspect of the iliac crest of the ilium.

The lumbar part of the longissimus thoracis originates from the lumbar intermuscular aponeurosis, anteromedial aspect of the sacropelvic surface of the ilium and the posterior sacroiliac ligament.

Insertion

The thoracic part of the longissimus thoracis inserts on the transverse processes of all twelve thoracic vertebrae (T1 - T12) and the angles of the seven to twelve ribs (7 - 12).

The muscle fibers of the lumbar part insert on the accessory and transverse processes of all lumbar vertebrae (L1 - L5).

Action

Muscle contractions on both sides (bilateral contractions) extend the thoracic and lumbar spine. Contractions on one side (unilateral contractions) provide lateral flexion of the thoracic and lumbar spine to the same side (ipsilateral).

Innervation

The longissimus thoracis is innervated by the lateral and medial branches of the dorsal rami of the thoracic and lumbar spinal nerves.

Blood supply

The longissimus thoracis is supplied by the branches of the posterior and superior intercostal arteries, lateral sacral and median sacral arteries. The posterior intercostal arteries arise from the superior intercostal arteries and thoracic aorta, while the superior intercostal arteries are branches of the costocervical trunk. The lateral sacral artery is a branch of the internal iliac artery, and the median sacral artery branches off the abdominal aorta.