Longissimus Muscle Anatomy

Location & Overview

The longissimus muscle is a large back muscle that runs parallel to the spine, extending from the sacrum to the edge of the mastoid process. It is divided into three sections, ordered from bottom to top: the longissimus thoracis, longissimus cervicis, and longissimus capitis. The longissimus is part of the erector spinae muscle group, alongside the iliocostalis and spinalis. The longissimus thoracis is the largest and longest muscle of the group and of the back, hence its name, “longissimus”.^[1,2] Examples of the longissimus sections and the erector spinae muscle group are displayed in the images below.

The longissimus muscle plays an important role in sporting activities, such as powerlifting, where it helps to maintain spinal extension during competition lifts like the deadlift and squat. In swimming, it helps to maintain proper body position, especially during freestyle and backstroke. The longissimus muscle is also important for day-to-day activities, such as twisting and bending. For example, when reaching for an object on a high shelf or bending over to put on shoes, it assists by stabilizing the spine and maintaining proper posture.

Origin & Insertion

The longissimus muscle has three sections, each with different points of origin and insertion. These are:

The longissimus capitis originates from the transverse processes of C4 to T4 vertebrae and inserts at the posterior edge of the mastoid process.^[3]

The longissimus cervicis originates from the transverse processes of T1 to T4 vertebrae and inserts at the posterior tubercle of C2 to C6 transverse processes.^[3]

The longissimus thoracis originates from the dorsal surface of the sacrum and its median sacral crest, the medial surface of the posterior superior iliac spine, and the transverse processes of L1 to L5 vertebrae. It inserts at the transverse processes of T1 to T12 vertebrae and the dorsal aspect of ribs 3 to 12, between the rib angle and tubercle.^[1]

Actions

The actions of the longissimus muscle depend on whether it contracts bilaterally (both sides contracting) or unilaterally (one side contracting). Bilateral contraction results in extension of both the trunk and the neck. Unilateral contraction results in lateral flexion of the trunk and the neck. However, it is important to note that the specific actions of each section of this muscle will depend on which portion of the spine they cross. To better understand which parts of the back are influenced by each section, you can refer to the accompanying illustrations above. For example, the capitis section originates from C4-T4 and inserts onto the mastoid process. Since the longissimus capitis is located near the top of the back and neck, the capitis section mainly influences movements at the neck and upper thoracic vertebrae. On the other hand, the longissimus thoracis ends before reaching the neck (at T1), so it has no actions at the neck but can influence movements of the trunk.^[1,2]

Innervation

The longissimus muscle is innervated by branches of the posterior rami of the corresponding spinal nerves. This pattern is typical of the intrinsic, or deep, muscles of the back. Each spinal level supplies the nearby part of the muscle, which means that the cervical, thoracic, and lumbar parts of the longissimus receive their nerve supply from the spinal nerves in their own region.^[4,5]

The longissimus capitis and longissimus cervicis are supplied by branches from cervical spinal nerves. These branches arise from the posterior rami and pass to the posterior neck muscles. The longissimus thoracis is supplied segmentally by posterior rami in the thoracic and lumbar regions. In the lumbar region, the longissimus is supplied by intermediate branches of the posterior rami, while the iliocostalis is supplied by lateral branches.^[5]

This segmental nerve supply reflects the long vertical course of the muscle. Rather than being supplied by one single named peripheral nerve, the longissimus receives small branches at different spinal levels. This arrangement helps each region of the muscle contribute to movement and postural control in the area of the spine that it crosses.^[4,5]

Blood Supply

The blood supply to the longissimus comes from several arteries because the muscle extends through the cervical, thoracic, lumbar, and sacral regions. In the neck, arterial supply comes from branches of the vertebral artery, deep cervical artery, occipital artery, and deep branch of the transverse cervical artery. These vessels supply the upper parts of the intrinsic back muscles, including the cervical and cranial portions of the longissimus.^[5]

In the thoracic region, the longissimus receives blood from dorsal branches of the posterior intercostal arteries. The upper thoracic supply includes contribution from the supreme intercostal artery through dorsal branches of the upper posterior intercostal arteries. Lower thoracic supply is provided by dorsal branches of the posterior intercostal arteries and subcostal arteries.^[5]

In the lumbar and sacral regions, the lower part of the longissimus receives blood from dorsal branches of the lumbar arteries, the arteria lumbalis ima when present, and dorsal branches of the lateral sacral arteries. This regional blood supply matches the long course of the muscle: nearby vessels supply the part of the muscle that lies in their anatomical region.^[5]