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Structure

Muscles of the back

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The back muscles form three groups: superficial (extrinsic, attaching the upper limb to the trunk), intermediate (respiratory, serratus posterior) and deep (intrinsic, moving and stabilising the vertebral column and head).

Terminologia Anatomica (Latin): Musculi dorsi · Open in the 3D atlas

Location

Superficial layer: trapezius and latissimus dorsi; deeper: levator scapulae, rhomboids. The deep (intrinsic) muscles lie in the groove beside the spinous processes, covered by the thoracolumbar fascia.

Structure

Deep muscles: erector spinae (iliocostalis, longissimus, spinalis), transversospinalis (semispinalis, multifidus, rotatores) and the small interspinales and intertransversarii; the splenius muscles (capitis, cervicis) lie superficially in the neck. Suboccipital muscles move the head at the atlanto-occipital and atlanto-axial joints.

Blood supply

Posterior branches of the intercostal, subcostal and lumbar arteries supply the deep muscles; the transverse cervical and dorsal scapular arteries supply trapezius and rhomboids; the thoracodorsal artery supplies latissimus dorsi; the occipital and vertebral arteries supply the suboccipital region.

Innervation

Deep muscles: posterior (dorsal) rami of spinal nerves. Trapezius: spinal accessory nerve (CN XI) plus C3-C4; latissimus dorsi: thoracodorsal nerve; rhomboids: dorsal scapular nerve; levator scapula: dorsal scapular and C3-C4; serratus posterior: intercostal nerves.

Function

Erector spinae extend and laterally flex the spine and maintain posture by continuous low-level activity; transversospinalis muscles rotate and stabilise segments; trapezius elevates, retracts and rotates the scapula; latissimus dorsi extends, adducts and medially rotates the arm; rhomboids retract the scapula.

Clinical correlations

Low back pain commonly arises from muscle strain, facet joints or disc disease; red-flag features (cauda equina symptoms, progressive deficit) require urgent assessment. Spinal accessory nerve injury (for example in neck surgery) causes trapezius weakness and a drooping shoulder; long thoracic nerve injury (serratus anterior, not a back muscle) causes winged scapula. The triangle of auscultation and lumbar triangle are anatomical weak points.

Common exam points

  • Three layers: superficial (trapezius, latissimus dorsi, rhomboids, levator scapulae), intermediate (serratus posterior), deep (erector spinae, transversospinalis).
  • Erector spinae lateral to medial: iliocostalis, longissimus, spinalis (I Love Spine).
  • All intrinsic back muscles are supplied by the posterior rami of spinal nerves; extrinsic muscles by the anterior rami or cranial nerve XI.
  • Trapezius is supplied by the spinal accessory nerve: test shoulder shrug.
  • Thoracolumbar fascia encloses the deep muscles; lumbar triangle is a site of rare hernias.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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