What Are the Paraspinal Muscles?

The paraspinal muscles are the "action" muscles of the back. When they work, the result is the obvious movement of your spine. They course down your back and spine and help to move your spine into extension, rotation, and side bending.

First, though, let's get our terms straight. The technical name for the paraspinals is the erector spinae; needless to say, many people have difficulty with the pronunciation. This may be why the word "paraspinals" and the term "paraspinal muscles" are commonly used to refer to this important group of back muscles.

Anatomy

The paraspinals are a set of three 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 three layers of the intrinsic back muscles are located beneath two more superficial back muscle groups which together make up the extrinsic back muscles.

The paraspinal muscles are located on the left and right side of your spine and are made up of three groups. These include:1

• Iliocostalis
• Longissimus
• Spinalis

These muscle groups attach at various parts of the cervical, thoracic, and lumbar spine. They usually course from the spinous process or transverse process of one vertebra to the spinous or transverse process of a vertebra one, two, or three levels below.

The paraspinals are innervated by nerves from the dorsal rami of the first cervical nerve down to the fifth lumbar nerve, depending on the level of the muscle.

 

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Function

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. If one is compromised, the resulting imbalance will affect the other, increasing the risk of chronic pain and injury.2

Chronic back pain is often related to the paraspinal muscles. Causes include poor posture (which places direct strain on the muscles), muscle strain, and muscle atrophy (in which the diminished muscle mass weakens spinal support).

Components

The paraspinal muscles run lengthwise along the spinal column, from the skull to the pelvis. While all three 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 three muscles that comprise the intermediate layer of the intrinsic back muscles are the iliocostalis, longissimus, and the spinalis.1

Iliocostalis Muscle

The iliocostalis muscle is the most lateral, or outside, of the three 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. This includes the ligaments that connect these processes to one another.

The Iliocostalis group is largely responsible for extension, flexion, and rotation of the spine, allowing us to bend backward and sideways and to twist the spinal column.

The iliocostalis is divided into three distinct parts:1

• 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 six or seven 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 six ribs. This portion also attaches to the back part of the transverse processes of the seventh cervical vertebra. The word cervical refers to the neck.
• The cervical portion of the iliocostalis muscle attaches to the back of the transverse processes of the fourth through the seventh cervical vertebrae.

Longissimus Muscle

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.

This also includes the ligaments that connect these processes to one another. The longissimus is situated between the iliocostalis and the spinalis.

Like the iliocostalis, the longissimus has three parts to it. But instead of lumbar, thoracic, and cervical parts, this muscle has thoracic, cervical, and cranial parts, each of which have specific functions:1

• The thoracic portion attaches to the tips of the transverse processes of all the thoracic vertebrae and by muscle branches to the lower nine or 10 ribs.
• The cervical portion of the longissimus attaches to transverse processes of the second through sixth 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 Muscle

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 three paraspinal muscles, the spinalis is the one closest to the midline. It, too, has three portions:1

• The thoracic portion attaches to the spinous processes of the upper four to eight (it can vary) thoracic vertebrae.
• The cervical portion inserts on the spinous process of the second cervical vertebra, called the axis, and sometimes on the spinous processes of one or two vertebra below that. It originates on the ligamentum nuchae from C4 to C6 and and spinous processes from C7 to T2.
• The capitis portion is often less distinguishable from the cervical portion but functions independently to help rotate, support, tilt, and move the head.