Rotatores - Deep Muscles of the Back

Little back muscles that provide a lot of functionality.

DEEP-ROTATORES
The deep rotatore muscles have special functions. By Anatomography (Anatomography 4.3) [CC-BY-SA-2.1-jp (http://creativecommons.org/licenses/by-sa/2.1/jp/deed.en)], via Wikimedia Commons/Altered by Anne Asher

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The rotatores group comprises the deepest layer of the intrinsic back muscles. The intrinsic back muscles, also known as the transversospinal muscles, consists of the splenius muscles (superficial layer), the paraspinal muscles (intermediate layer) and the deep layer which consists of 4 muscle groups: The interspinalis, intertransverse, multifidus and rotatores group.

Related:  Extrinsic Back Muscles

(Note: The number of muscle groups that comprise the deepest layer of the intrinsic back muscles can vary by author or researcher. Some authors portray the intertransverse and interspinalis muscles as on their own, and as such not a part of the intrinsic - or transversospinalis - layer at all.)

The rotatores are small muscles shaped like a quadralateral that arise from the transverse processes of the vertebrae on which this muscle is found, and attach onto the lamina on a spinal bone located above.

The rotatores are found underneath the multifidus, a location that can also be phrased "deep to the multifidus." Depending on if the rotatore muscle is short (called rotatore brevis) or long (rotatore longus), it will angle inward and up for either one or two levels. (The rotatore brevis will attach 1 level up from where it originates, while the rotatores longus will attach 2 levels up.)

THE JOBS OF THE ROTATORES

The entire intrinsic layer of the back produces spinal extension.

It also helps produce lateral flexion (side bending) and rotation (twisting). As a part of the team, the rotatores may contribute to these actions, but as you will see next, they also have a couple of other functions that distinguish them from their co-contractors.

The function of the rotatores is not well known.

While they are grouped with all the other spinal extensor muscles (discussed above), because of their small size, they are at a mechanical disadvantage when it comes to actually producing spinal motion. It is thought that the rotatores play a role in stiffening or stabilizing the spine.

Along with their likely contribution to spinal stabilization, the rotatores also serve as a sort of motion monitor, providing feedback about the precise location of the spinal bones they affect. In 1986, researchers Nitz and Peck found many more muscle spindles in the short rotatores (rotatore brevis) than in the other spinal muscles. (Their research was published in the May 1986 issue of American Surgery.)

What is a muscle spindles, you ask?

Essentially, muscle spindles are nerve endings that function a lot like a sensor chip inside a camera.

Muscle spindles are located deep inside the belly of the muscle, and their job is to pick up information about the length of the muscle (which is related to how contracted or relaxed the muscle fibers are at any given moment.) The muscle spindles are "wired" to relay this information to your central nervous system for processing.

The information then influences the other spinal muscles as they go about producing spinal movement, and stabilization for your spine.

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Sources:

Clippinger, K. Dance Anatomy and Kinesiology. Human Kinetics. Champaign, Illinois. 2007. http://books.google.com/books?id=PCKxhwL1sSQC&pg=PA88&lpg=PA88&dq=the+rotatores+span+between+how+many+vertebrae&source=bl&ots=UtUHqseLL5&sig=0J7uGU_HXnw-mJLdju7DIensStc&hl=en&sa=X&ei=IGNNVKD4OIqYyQT904A4&ved=0CD8Q6AEwBQ#v=onepage&q=the%20rotatores%20span%20between%20how%20many%20vertebrae&f=false

Emory University. The Vertebral Column and the Spinal Cord. Anatomy Manual web page. http://www.emory.edu/ANATOMY/AnatomyManual/back.html Accessed. Oct 26 2014.

University of Michigan. Muscles of the Back Region - Listed Alphabetically. Medical Gross Anatomy: Anatomy Tables - Muscles. University of Michigan Medical School http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/anatomytables/muscles_back.html. Accessed: October 26, 2014.

Nitz AJ, Peck D. Comparison of muscle spindle concentrations in large and small human epaxial muscles acting in parallel combinations. Am Surg. 1986 May;52(5):273-7. http://www.ncbi.nlm.nih.gov/pubmed/2422993

University of Washington. Propriceptors. http://courses.washington.edu/conj/bess/spindle/proprioceptors.html Accessed Oct 26 2014.

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