Longissimus Thoracis (Lumbar Part)
Back · Trunk
The lumbar part of longissimus thoracis is the deep lumbar contribution to the longissimus column, sometimes described separately because of its distinct lumbar attachments. It arises from the accessory and transverse processes of the lumbar vertebrae and runs downward and laterally to attach to the medial part of the iliac crest through the lumbar intermuscular aponeurosis. Because its fibres bridge each lumbar vertebra to the pelvis, contraction on both sides extends the lumbar spine and contraction on one side laterally flexes it. Like the rest of the deep back muscles, it is supplied by the posterior (dorsal) rami of the lumbar spinal nerves. Its segmental pelvis-to-vertebra arrangement makes it an important stabiliser of the individual lumbar segments during posture and lifting.
Origin, Insertion, Action & Nerve
Origin
Accessory and transverse processes of the lumbar vertebrae
Insertion
Medial part of the iliac crest via the lumbar intermuscular aponeurosis
Action
Bilaterally extends the lumbar spine; unilaterally laterally flexes it
Nerve
Posterior (dorsal) rami of lumbar spinal nerves
Attachments explained
The Longissimus Thoracis (Lumbar Part) 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
Accessory and transverse processes of the lumbar vertebrae
Insertion
Medial part of the iliac crest via the lumbar intermuscular aponeurosis
Action & function
When the Longissimus Thoracis (Lumbar Part) contracts, it produces the following movements: Bilaterally extends the lumbar spine; 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 (Lumbar Part) receives its nerve supply from the Posterior (dorsal) rami of lumbar spinal nerves.
Because a muscle can only contract when its nerve is intact, injury to the Posterior can weaken or paralyse the Longissimus Thoracis (Lumbar Part), impairing the movements it normally produces (bilaterally extends the lumbar spine). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Longissimus Thoracis (Lumbar Part) (the OIANS method)
Learn this part as the segmental lumbar anchor of longissimus: it links each lumbar transverse and accessory process directly to the iliac crest through the lumbar intermuscular aponeurosis. That short, near-vertical pull from vertebra to pelvis is why its main jobs are lumbar extension and same-side bending, and why anatomists single it out from the longer thoracic fibres above it.
Contrast it with the main longissimus thoracis to avoid overlap. The parent muscle sweeps up to thoracic transverse processes and lower ribs, whereas this lumbar part descends to the iliac crest and specialises in controlling the lumbar segments themselves. Tie it in your mind to the quadratus lumborum region as another deep player in lumbar stability, but remember it is a dorsal-ramus erector spinae muscle rather than an abdominal-wall one.
Frequently asked questions
Where is the Longissimus Thoracis (Lumbar Part) located?
The Longissimus Thoracis (Lumbar Part) is a muscle of the Back group, located in the Trunk.
What is the origin of the Longissimus Thoracis (Lumbar Part)?
Accessory and transverse processes of the lumbar vertebrae
What is the insertion of the Longissimus Thoracis (Lumbar Part)?
Medial part of the iliac crest via the lumbar intermuscular aponeurosis
What movements does the Longissimus Thoracis (Lumbar Part) produce?
Bilaterally extends the lumbar spine; unilaterally laterally flexes it
What nerve supplies the Longissimus Thoracis (Lumbar Part)?
Posterior (dorsal) rami of lumbar spinal nerves
Is the Longissimus Thoracis (Lumbar Part) free to study in OIANS?
The Longissimus Thoracis (Lumbar Part) 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
Study the Longissimus Thoracis (Lumbar Part)
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