Semispinalis Thoracis
Back · Trunk
Semispinalis thoracis is the thoracic part of the semispinalis, the most superficial of the transversospinales muscles that span several vertebral segments. It arises from the transverse processes of the middle thoracic vertebrae (T6-T10) and its fibres run upward and medially across four to six segments to insert on the spinous processes of the lower cervical and upper thoracic vertebrae (C6-T4). This diagonal, transverse-to-spinous course allows it to extend the thoracic and cervical spine and to rotate the trunk toward the opposite side. It is supplied by the posterior (dorsal) rami of the thoracic spinal nerves. As a long, thin muscle bridging many segments, it acts largely as a postural stabiliser of the upper back.
Origin, Insertion, Action & Nerve
Origin
Transverse processes of T6–T10
Insertion
Spinous processes of C6–T4
Action
Extends the thoracic and cervical spine and rotates it to the opposite side
Nerve
Posterior (dorsal) rami of thoracic spinal nerves
Attachments explained
The Semispinalis Thoracis is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Transverse processes of T6–T10
Insertion
Spinous processes of C6–T4
Action & function
When the Semispinalis Thoracis contracts, it produces the following movement: Extends the thoracic and cervical spine and rotates it to the opposite side.
As part of the Back group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Semispinalis Thoracis receives its nerve supply from the Posterior (dorsal) rami of thoracic spinal nerves.
Because a muscle can only contract when its nerve is intact, injury to the Posterior can weaken or paralyse the Semispinalis Thoracis, impairing the movements it normally produces (extends the thoracic and cervical spine and rotates it to the opposite side). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Semispinalis Thoracis (the OIANS method)
Learn semispinalis thoracis by its defining diagonal: fibres travel from thoracic transverse processes up and across to spinous processes several levels higher. This transverse-to-spinous direction is the hallmark of the transversospinales, and it is exactly why the muscle both extends the spine and rotates it to the opposite side, unlike the purely vertical spinalis nearby.
Pair the semi in its name with the idea that it spans about half the length between origin and destination in long, obliquely oriented fibres crossing four to six segments. Study it as the thoracic member of the semispinalis trio (thoracis, cervicis, capitis) and let the contralateral rotation action carry across all three, since that opposite-side turn distinguishes semispinalis from the same-side rotation of longissimus capitis.
Frequently asked questions
Where is the Semispinalis Thoracis located?
The Semispinalis Thoracis is a muscle of the Back group, located in the Trunk.
What is the origin of the Semispinalis Thoracis?
Transverse processes of T6–T10
What is the insertion of the Semispinalis Thoracis?
Spinous processes of C6–T4
What movements does the Semispinalis Thoracis produce?
Extends the thoracic and cervical spine and rotates it to the opposite side
What nerve supplies the Semispinalis Thoracis?
Posterior (dorsal) rami of thoracic spinal nerves
Is the Semispinalis Thoracis free to study in OIANS?
The Semispinalis Thoracis is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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