Longissimus Thoracis

Back · Trunk

The Longissimus Thoracis is a Trunk muscle within the Back group. Originating at Posterior sacrum, transverse and accessory processes of the lumbar vertebrae, and thoracolumbar fascia, it inserts at Transverse processes of all thoracic vertebrae and angles of the lower nine or ten ribs. It is responsible for several movements: Bilaterally extends the vertebral column; unilaterally laterally flexes it. Its nerve supply is the Posterior (dorsal) rami of spinal nerves.

Origin, Insertion, Action & Nerve

Origin

Posterior sacrum, transverse and accessory processes of the lumbar vertebrae, and thoracolumbar fascia

Insertion

Transverse processes of all thoracic vertebrae and angles of the lower nine or ten ribs

Action

Bilaterally extends the vertebral column; unilaterally laterally flexes it

Nerve

Posterior (dorsal) rami of spinal nerves

Attachments explained

The Longissimus 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

Posterior sacrum, transverse and accessory processes of the lumbar vertebrae, and thoracolumbar fascia

Insertion

Transverse processes of all thoracic vertebrae and angles of the lower nine or ten ribs

Action & function

When the Longissimus Thoracis contracts, it produces the following movements: Bilaterally extends the vertebral column; unilaterally laterally flexes it.

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 Longissimus Thoracis receives its nerve supply from the Posterior (dorsal) rami of spinal nerves.

Because a muscle can only contract when its nerve is intact, injury to the Posterior can weaken or paralyse the Longissimus Thoracis, impairing the movements it normally produces (bilaterally extends the vertebral column). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Longissimus Thoracis (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Longissimus 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 Longissimus 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.