Anatomy

Vertebral Column & Back Musculature: Intermediate Back

Anisha ValliLeave a comment

Deeper layer =

Erector spinae, from medial to lateral:

  • Spinalis, Longissimus, and Iliocostalis.

Spinalis:

  • Originates on the thoracic vertebrae and the first two lumbar vertebrae (specifically¬, from their spinous processes).
  • Inserts along the vertebral column as superiorly as the 2nd and 3rd cervical vertebrae. It sometimes has a cervical portion that inserts on the base of the skull.

Longissimus:

  • Originates on the transverse processes of the lumbar, thoracic, and cervical vertebrae
  • Inserts along the ribs and vertebral column (as superiorly as C2).
  • It also sends a portion of muscle to attach to the mastoid processes on the skull.

Iliocostalis:

  • Originates on the sacrum and ilia.
  • Inserts along the ribs and vertebral column as superiorly as cervical vertebrae 4-7.

Additional information about the erector spinae:

  • These muscles comprise many short segments of muscle fibers.
  • The erector spinae muscles are prone to injury as a result of improper heavy lifting.
  • When contracted bilaterally, the erector spinae muscles extend the back;
    Unilateral contraction produces lateral flexion of the back (moves the shoulder towards the lateral hip of the same side).
  • The erector spinae muscles can be further subdivided according to vertical region:
    For example, the portion of iliocostalis that lies within the lumbar region is referred to as iliocostalis lumborum; the portion of spinalis that lies with the thoracic region is referred to as spinalis thoracis, and so on.

Superficial layer =

Serratus posterior superior:

  • Originates on vertebrae C7-T3 (specifically, from their spinous processes and associated connective tissues), extends inferolaterally
  • Inserts as thin strips of muscle, on ribs 2-5, lateral to the erector spinae.
  • Elevates ribs 2-5 during forced inspiration.

Serratus posterior inferior:

  • Originates on vertebrae T12-L3
  • Inserts superolaterally on ribs 9-12 (specifically, to their inferior borders).
  • Depresses ribs 9-12 during forced expiration.
  • Serratus posterior superior and inferior muscles are mirror images of each other.
  • The thoracolumbar fascia separates the erector spinae and serratus posterior superior and inferior muscles.

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