Longissimus Thoracis
Back · Trunk
Longissimus thoracis is the largest and most substantial part of the longissimus column, forming the bulk of the erector spinae in the thoracic and lumbar regions. It arises broadly from the posterior surface of the sacrum, the transverse and accessory processes of the lumbar vertebrae, and the thoracolumbar fascia, and its long fibres insert on the transverse processes of all the thoracic vertebrae and on the angles of the lower nine or ten ribs. Acting on both sides it is a powerful extensor of the vertebral column, and acting on one side it laterally flexes the trunk toward that side. It is innervated segmentally by the posterior (dorsal) rami of the spinal nerves. Its rib attachments also let it help steady the thorax during the demands of breathing and posture.
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)
Treat longissimus thoracis as the workhorse of the back extensors. Its wide sacral, lumbar, and fascial origin gives it a strong anchor from which its fibres sweep up to the thoracic transverse processes and the lower ribs, and that geometry explains why bilateral contraction straightens the whole column while unilateral contraction tips it sideways. Feel the muscle tense along either side of the spine when you lift your chest from a bent-forward position.
Anchor its dual insertion to keep it distinct from its cervical and cranial namesakes: this member reaches both transverse processes and the angles of the lower ribs, a rib attachment its capitis and cervicis siblings lack. Remember it lies medial to iliocostalis and lateral to spinalis within the erector spinae, so its central column position pairs with its central role in posture and lifting.
Frequently asked questions
Where is the Longissimus Thoracis located?
The Longissimus Thoracis is a muscle of the Back group, located in the Trunk.
What is the origin of the Longissimus Thoracis?
Posterior sacrum, transverse and accessory processes of the lumbar vertebrae, and thoracolumbar fascia
What is the insertion of the Longissimus Thoracis?
Transverse processes of all thoracic vertebrae and angles of the lower nine or ten ribs
What movements does the Longissimus Thoracis produce?
Bilaterally extends the vertebral column; unilaterally laterally flexes it
What nerve supplies the Longissimus Thoracis?
Posterior (dorsal) rami of spinal nerves
Is the Longissimus Thoracis free to study in OIANS?
The Longissimus 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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