Semispinalis thoracis muscle

At a glance

English

Semispinalis thoracis muscle

Latin (TA2)

Musculus semispinalis thoracis

System

Muscle

Region

Back

Side

Paired, left and right

About the semispinalis thoracis muscle

Semispinalis thoracis, also called semispinalis dorsi, is the lowest and thinnest part of semispinalis, one of the transversospinal muscles that lie in the groove beside the spinous processes. It sits beneath the erector spinae and above multifidus, and is continued upward by semispinalis cervicis.

It is made of narrow fleshy bundles separated by long tendons. These arise by small tendons on the transverse processes of T6 to T10. They climb upward and inward over five or six segments and end, again by tendons, on the spines of C6 and C7 and the upper four thoracic vertebrae.

Acting on both sides, the muscle extends the thoracic spine and the lower neck. Acting on one side, it rotates these segments so that the trunk turns towards the opposite side. With the other transversospinal muscles it controls the posture of the upper back. Its long tendons make it less powerful than its fleshy neighbours, but they let it act across a long stretch of the spine, linking the middle of the thorax to the base of the neck.

It is supplied segment by segment by medial branches of the dorsal rami of the thoracic spinal nerves, and blood reaches it from the dorsal branches of the posterior intercostal arteries. It is seldom affected on its own, but it shares in the stiffness and aching of the upper back that comes with poor posture.

Attachments, action and supply

Origin

Transverse processes of T6 to T10.

Insertion

Spines of C6 and C7 and of T1 to T4.

Action

Extends the thoracic spine and lower neck; on one side rotates them towards the opposite side.

Nerve supply

Medial branches of the dorsal rami of the thoracic spinal nerves.

Blood supply

Dorsal branches of the posterior intercostal arteries.