Spinalis Thoracis
Back · Trunk
Spinalis thoracis is the best-developed part of the spinalis column and the most medial component of the erector spinae in the thoracic region. It arises from the spinous processes of the lower thoracic and upper lumbar vertebrae (T11-L2) and ascends to insert on the spinous processes of the upper thoracic vertebrae (roughly T1-T8), lying immediately alongside the midline. Its near-vertical fibres extend the thoracic vertebral column. It is innervated by the posterior (dorsal) rami of the thoracic spinal nerves. Because it connects lower spinous processes to upper ones, it works with longissimus and iliocostalis to keep the trunk upright, contributing the medial column of that combined extensor mass.
Origin, Insertion, Action & Nerve
Origin
Spinous processes of T11–L2
Insertion
Spinous processes of the upper thoracic vertebrae (T1–T8)
Action
Extends the thoracic vertebral column
Nerve
Posterior (dorsal) rami of thoracic spinal nerves
Attachments explained
The Spinalis 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
Spinous processes of T11–L2
Insertion
Spinous processes of the upper thoracic vertebrae (T1–T8)
Action & function
When the Spinalis Thoracis contracts, it produces the following movement: Extends the thoracic vertebral column.
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 Spinalis 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 Spinalis Thoracis, impairing the movements it normally produces (extends the thoracic vertebral column). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Spinalis Thoracis (the OIANS method)
Fix spinalis thoracis as the clearest example of the spinalis pattern: spinous process origin to spinous process insertion, right next to the midline. Its lower thoracic and upper lumbar spines feed fibres up to the upper thoracic spines, a purely vertical arrangement that makes thoracic extension its single, unambiguous action. If you can see it as a chain linking one row of spines to another, the muscle is learned.
Use its position to complete your mental map of the erector spinae: iliocostalis is the lateral column, longissimus the intermediate, and spinalis the medial one, and thoracis is the most substantial spinalis segment. Contrast its spinous-process attachments with the transverse-process attachments of the nearby semispinalis thoracis, which also crosses several segments but rotates the trunk to the opposite side rather than simply extending it.
Frequently asked questions
Where is the Spinalis Thoracis located?
The Spinalis Thoracis is a muscle of the Back group, located in the Trunk.
What is the origin of the Spinalis Thoracis?
Spinous processes of T11–L2
What is the insertion of the Spinalis Thoracis?
Spinous processes of the upper thoracic vertebrae (T1–T8)
What movements does the Spinalis Thoracis produce?
Extends the thoracic vertebral column
What nerve supplies the Spinalis Thoracis?
Posterior (dorsal) rami of thoracic spinal nerves
Is the Spinalis Thoracis free to study in OIANS?
The Spinalis 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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