Intrinsic Back Muscles: Deep and Minor Layers
Transversospinalis: Semispinalis, multifidus, and rotatores.
Minor muscles of the back: levator costarum, interspinales, and intertransversarii.
Semispinalis arises from the transverse processes of C4-T12 and inserts on the occipital bone and on the spinous processes of the cervical and thoracic vertebrae.
Semispinalis is a paired muscle that comprises cervicis, thoracis, and capitis portions; It extends and rotates the head and vertebral column. Be careful not to confuse it with spinalis of the erector spinae muscle group; semispinalis is deeper than spinalis.
Multifidus comprises several short bundles of muscle tissue that arise and insert along both sides of the vertebral column.
Multifidus arises from the sacrum and the transverse processes of the vertebral column and insersts on the spinous processes of the vertebrae.
Multifidus extends of the vertebral column and neck, and rotates the vertebral column to the opposite side.
Rotatores arise from the transverse processes of the vertebrae and insert on the spinous processes of the vertebrae immediately superior to their origin.
Their zig-zag-like pattern can be better visualized in our non-expanded view – notice how the rotatores zig-zag between the transverse and spinous processes. These muscles can be further divided into "longus" and "brevis" based on their positioning in the pattern.
The rotatores extend the vertebral column and neck and rotate the vertebral column to the opposite side.
Levator costarum arises from the transverse processes of C7-T11 and inserts on the rib below each origin point; this is the most lateral attachment point we'll see in this tutorial.
As you can probably guess from its name, levator costarum elevates the ribs during inspiration.
Interspinales fibers travel between the spinous processes of adjacent vertebrae – "spinales" refers to the spinous processes. These muscles aid in extension and rotation of the vertebral column.
Intertransversarii fibers extend between the transverse processes of adjacent vertebrae – notice the "transvers" in the name, for transverse processes. These muscles aid in lateral flexion of the vertebral column.
