Spinalis Thoracis

Back · Trunk

Spinalis Thoracis belongs to the Back group of the Trunk. It arises from Spinous processes of T11–L2 and attaches to Spinous processes of the upper thoracic vertebrae (T1–T8). Its chief action is that it extends the thoracic vertebral column. Its nerve supply is the Posterior (dorsal) rami of thoracic spinal nerves.

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)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Spinalis Thoracis, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Spinalis Thoracis fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.