Erector Spinae
Back · Trunk
The erector spinae is the great vertical muscle mass of the back, the main extensor of the vertebral column that runs on either side of the spinous processes from the sacrum to the skull. It arises from a broad common tendon attached to the posterior sacrum, the iliac crest, the sacrospinous and supraspinous ligaments, and the lumbar spinous processes, then splits into three parallel columns. From lateral to medial these are iliocostalis, which reaches the ribs and cervical transverse processes; longissimus, which reaches the transverse processes and the mastoid process; and spinalis, which reaches the spinous processes. Acting bilaterally it extends the vertebral column and head, while acting on one side it laterally flexes the column. It is supplied segmentally by the dorsal rami of the spinal nerves. During forward bending it works eccentrically to control descent, which is why the lower back is a common site of muscular strain.
Origin, Insertion, Action & Nerve
Origin
Common tendon from posterior sacrum, iliac crest, sacrospinous/supraspinous ligaments, and lumbar spinous processes
Insertion
Iliocostalis: ribs and cervical transverse processes; Longissimus: transverse processes and mastoid process; Spinalis: spinous processes
Action
Bilateral: extension of vertebral column and head; Unilateral: lateral flexion of vertebral column
Nerve
Dorsal rami of spinal nerves (segmental)
Attachments explained
The Erector Spinae 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
Common tendon from posterior sacrum, iliac crest, sacrospinous/supraspinous ligaments, and lumbar spinous processes
Insertion
Iliocostalis: ribs and cervical transverse processes; Longissimus: transverse processes and mastoid process; Spinalis: spinous processes
Action & function
When the Erector Spinae contracts, it produces the following movements: Bilateral: extension of vertebral column and head; Unilateral: lateral flexion of 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 Erector Spinae receives its nerve supply from the Dorsal rami of spinal nerves (segmental).
Because a muscle can only contract when its nerve is intact, injury to the Dorsal rami of spinal nerves can weaken or paralyse the Erector Spinae, impairing the movements it normally produces (extension of vertebral column and head). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Erector Spinae (the OIANS method)
Master the erector spinae by fixing its three columns in order from the midline outward: spinalis nearest the spinous processes, longissimus in the middle reaching up to the mastoid process, and iliocostalis most lateral on the ribs. The mnemonic I Love Spaghetti, read lateral to medial, keeps iliocostalis, longissimus, and spinalis in the right sequence.
Reason about its actions from the fact that the fibres run vertically behind the axis of the spine, so a bilateral pull straightens and extends the column while a one-sided pull bends it to that side. Remembering that it is supplied segmentally by dorsal rami, rather than by a single named nerve, reflects its long, multi-level design and separates it from the limb muscles that have discrete nerves.
Frequently asked questions
Where is the Erector Spinae located?
The Erector Spinae is a muscle of the Back group, located in the Trunk.
What is the origin of the Erector Spinae?
Common tendon from posterior sacrum, iliac crest, sacrospinous/supraspinous ligaments, and lumbar spinous processes
What is the insertion of the Erector Spinae?
Iliocostalis: ribs and cervical transverse processes; Longissimus: transverse processes and mastoid process; Spinalis: spinous processes
What movements does the Erector Spinae produce?
Bilateral: extension of vertebral column and head; Unilateral: lateral flexion of vertebral column
What nerve supplies the Erector Spinae?
Dorsal rami of spinal nerves (segmental)
Is the Erector Spinae free to study in OIANS?
The Erector Spinae 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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