Function and Anatomy of Erector Spinae Muscles

The presence of a large number of Type 1 muscle fibers (slow twitch or red muscle fibers that arerich in myoglobulin and carry more oxygen) in the erector spinae muscle group makes it resistant tofatigue.

A vital part of the human anatomy, muscles are soft tissues that facilitate locomotion. They allow usto change or maintain posture. The ability of the human spine to bend forward or backward, rotate,or twist, is attributed to several layers of muscles that support the back.

Erector spinae muscles, also referred to as the sacrospinal muscle group, is one such muscle groupthat primarily acts as an extensor. It consists of three muscles that help in extending the vertebralcolumn. This muscle group runs from the base of the skull to the sacrum. Basically, it consists ofthree columns of muscles that are present on either side of the vertebral column. These are knownas Iliocostalis, Longissimus, and Spinalis. Spinalis muscle lies closest to the vertebral column. Itbegins as a thick tendon from the sacrum and travels up. The longest of these three muscles,longissimus inserts at the mastoid process, which is the temporal process that is located behind theear, at the base of the skull. Iliocostalis lies furthest from the vertebral column, and extends from thebase of the skull to the pelvis.

Location of Erector Spinae Muscles

The erector spinae is one of the three true or intrinsic back muscles. It is this muscle group thatallows the spine to return to erect position after bending. We bend backwards when these musclescontract, and when only the muscles on one side of the vertebral column contract, we are able tobend sideways. So, these muscles allow us to bend sideways, and facilitate the rotation of the spineand movement of the head. These help in maintaining the alignment of the spine.

Anatomy and Function of Erector Spinae Muscles

Iliocostalis Muscles

Iliocostalis Cervicis

Arising from the angles of the third, fourth, fifth, and the sixth pair of ribs, Iliocostalis cervicismuscle inserts at the transverse process of the cervical vertebrae C4 to C6. This muscle helps inextending and hyperextending the cervical vertebrae. It also facilitates the lateral flexion of thecervical vertebrae.

Iliocostalis Thoracis

Arising from the upper borders of the angles of the inferior six ribs (seventh to the twelfth pair ofribs), Iliocostalis thoracis muscle inserts into the upper borders of the angles of first to the sixth pairof ribs, and into the posterior transverse process of the C7, which is the seventh cervical vertebra. Ithelps in maintaining the erect posture of the spine

Iliocostalis lumborum

The insertion point of the iliocostalis lumborum are the inferior borders of the angles of the last pair

of the true ribs (seventh rib), and the false and floating ribs, which means eighth to twelfth pair ofribs. It also inserts in the transverse processes of the first five lumbar vertebrae (L1-L5). This muscleplays a vital role in the extension of the vertebral column. When we bend forward, it providesresistance, and also helps in providing the force that is needed for bringing the body back to itsnormal, erect position. When we bend completely to touch our toes, these muscles are relaxed, whilethe load is on the ligaments, and on returning to the normal position, these muscles pass on the loadto the hamstrings and the gluteus maximus, which is the outermost of the three gluteal muscles.

Longissimus Muscles

Longissimus Cervicis

Arising from the transverse processes of the upper five thoracic vertebrae (T1 to T5), this muscleinserts in the transverse processes of the second to sixth cervical vertebrae. It helps in extending thecervical region of the vertebral column and maintaining the erect posture. It is also lends stability tothe spinal column during flexion. When only the muscle on one of the sides is working, it helps inbending and rotating to that particular side.

Longissimus Thoracis

It arises from the sacrum and medial iliac crest through the iliocostalis lumborum tendon andlumbosacral aponeurosis, and the transverse and spinous processes of vertebrae of the lumbarregion. It inserts in the transverse processes of the thoracic vertebrae. It helps in extending thethoracic region or the lower vertebral column.

Longissimus Capitis

It arises from the transverse and the articular processes of the middle and lower cervical vertebrae(C4 or C5-C7), and the transverse processes of the upper thoracic vertebrae (T1-T5). It inserts intothe posterior aspect of the mastoid process of the temporal bone. It helps extend the head and rotateit to the opposite side.

Spinalis Muscles

The function of the spinalis muscle is to extend the vertebral column, and laterally bend the neckand trunk.

Spinalis Thoracis

This muscle arises from the spinous process of the lower thoracic vertebrae (T11) or lumbarvertebrae (L2-L3). It inserts into the spinous processes of the third to eight thoracic vertebrae. Itsfunction is similar to that of the other erector spinae muscles, i.e., extension of the vertebral column.It also helps maintain erect posture. Also, it will help in bending and twisting to the same side.

Spinalis Cervicis

This muscle arises from the lower ligamentum nuchae and the spinous processes of the sixth orseventh cervical vertebrae (sometimes first or second thoracic vertebrae). It inserts into the spinousprocesses of the axis, or sometimes the third or fourth cervical vertebrae.

Spinalis Capitis

This muscle arises from the spinous processes of the lower cervical vertebrae and upper thoracicvertebrae. The insertion points are between the superior and the inferior nuchal lines of the occipitalbone at the base of the skull.

On a concluding note, erector spinae muscles are extremely essential for stabilizing or strengtheningthe back. Though these muscles are quite strong due to the presence of Type 1 fibers, excessivestrain can have an adverse effect on them, thereby causing back pain.