What Are the Paraspinal Muscles?

Where are they and what do they do?

Back muscles
Back muscles. SPRINGER MEDIZIN / Getty Images

Paraspinal Muscles

The paraspinal muscles are the “action” back muscles. When they work, the result is the obvious movement of your spine. This article explains where these muscles are relative to the other spinal structures (in back) and what they do.

First, though, let's get our terms straight. The technical name for the paraspinals is the erector spinae, although many people have difficulty with the pronunciation.

Luckily the word "paraspinals" and the term "paraspinal muscles" are common ways to refer to this important group of back muscles.

What are the paraspinal muscles?

The paraspinals are a set of 3 muscles occupying what is known as the intermediate layer of the intrinsic back muscles. As the name suggests, the intermediate layer is located above the deep layer, and beneath the superficial layer. The entire 3 layers of the intrinsic back muscles are located beneath 2 more superficial back muscle groups which together make up the extrinsic back muscles.

The job of the paraspinal muscles is to extend your spine, and to bend it over to the same side on which the contracting paraspinal muscle is located.

Many people equate a spinal extension motion with back arching, which may be a good way to think about it when you describe or attempt this kind of movement. 

The contraction of paraspinal muscles also serves to "check" the action of the abdominal muscles.

In other words, the abdominal muscles, particularly the rectus abdominus, bend the trunk forward. As this movement occurs, an eccentric contraction (where the muscle elongates as it contracts) of the paraspinals keeps the trunk from bending too fast, as well as going too far forward. The abdominals and paraspinals work together to help maintain upright body posture by this same mechanism.

Related: Spinal Motions: Flexion and Extension

Location of the Paraspinal Muscles

The paraspinal muscles run lengthwise along the spinal column, from the skull to the pelvis. While all 3 start at the same place - specific areas at the lowest area of the spine - and all have a lumbar, thoracic and cervical part, their muscle fibers insert onto varying aspects of the spinal vertebrae and ribs.

The 3 muscles that comprise the intermediate layer of the intrinsic back muscles are the iliocostalis, longissimus, and the spinalis.

Iliocostalis

The iliocostalis muscle is the most lateral (outside) of the 3 paraspinal muscles.  It originates from a broad tendon on the back of the hip bones, the back of the sacrum bone, the ligaments of the sacroiliac joints, and the spinous processes of the lower lumbar vertebra (including the ligaments that connect these processes to one another.)  

The lumbar portion of the iliocostalis muscle travels upward from the lower area of the pelvis and sacrum to attach onto the lower border of the bottom 6 or 7 ribs, by means of tendons that branch off from the main line.

 The thoracic portion also attaches to ribs, but these are the top part of the upper 6 ribs. This portion also attaches on the back part of the transverse processes of the 7th cervical (neck) vertebra. The cervical portion of the iliocostalis muscle attaches onto the back of the transverse processes of the 4th through the 7th cervical vertebrae.

Related:  The Sacroiliac Joint

Longissimus

Like the iliocostalis muscle, the longissimus originates from a broad tendon on the back of the hip bones, the back of the sacrum bone, the ligaments of the sacroiliac joints, and the spinous processes of the lower lumbar vertebra (including the ligaments that connect these processes to one another.) It is situated between the iliocostalis and the spinalis (see below for a discussion on the spinalis).

Related: Spinal Ligaments

And like the iliocostalis, the longissimus has 3 parts to it. But instead of lumbar, thoracic and cervical parts, this muscle has thoracic, cervical and cranial (head or skull) parts. Tendons of the thoracic part attach to the tips of the transverse processes of all the thoracic vertebrae and by muscle branches to the lower 9 or 10 ribs.

The cervical portion of the longissimus attaches to transverse processes of the 2nd through 6th cervical vertebrae.

The cranial portion attaches to a projection of bone known as the mastoid process, which is located at the back of the skull, right behind the bottom of the ear.

Spinalis

Like the iliocostalis and longissimus muscles, the spinalis originates from a broad tendon on the back of the hip bones, the back of the sacrum bone, the ligaments of the sacroiliac joints, and the spinous processes of the lower lumbar vertebra (including the ligaments that connect these processes to one another.)

Of the 3 paraspinal muscles, the spinalis is the one closest to the vertebral column. It, too, has 3 portions: The thoracic, the cervical and the capitis.

The thoracic portion attaches on the spinous processes of the upper 4 to 8 (it can vary) thoracic vertebrae. The cervical portion attaches on the spinous process of the 2nd cervical vertebra (called the axis) and sometimes on the spinous processes of 1 or 2 vertebra below that. The cervical portion attaches to the mastoid process, which is the same site for the cranial portion of the longissimus muscle.

Related: Thoracic Spine Pain

Sources

Kendall, F., McCreary, E. Provance, P. Muscles: Testing and Function. 4th edition. Williams & Wilkins. Baltimore, MD. 1993

Moore, K., Dalley, A. Clinically Oriented Anatomy. Fifth. Edition. Lippincott, Williams & Wilkins. 2006. Baltimore. Philadelphia, PA

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