Semispinals Back Muscle Group

Superficial Layer of Deep Intrinsic Spinal Extensors

The semispinalis muscle group, consisting of three muscles, is the most superficial of your deep intrinsic back muscles. The deep layer of muscles is called the transversospinalis group.

The semispinalis muscles work to extend your head, neck, and upper back. They also laterally flex your head and neck towards the ipsilateral (same side) of your body and turn your head, neck, and upper back towards the opposite side of your body.

A muscular man's back

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Fibers of the semispinalis muscles attach to your spinous processes, which are the bony projections that extend out from the center of the back of each vertebra. When these voluntary muscles contract (shorten), they cause movements of your body.

The 3 separate muscles each have their own movements, and they also work together.

Semispinalis Thoracis

The semispinalis thoracis extends your spine, rotates it towards the side of your body that is opposite from this muscle, and performs ipsilateral flexion. For example, if you turn to look over your right shoulder while parallel parking, you'll likely be involving the semispinalis thoracis that is located on the left side of your spine.

The semispinalis thoracis is the most superficial layer of the semispinalis muscle group. Superficial, in this case, refers to the muscles closest to the skin relative to the other muscles in the group

The semispinalis thoracis:

  • Arises from the transverse process of the lower thoracic vertebrae of the thoracic spine
  • Attaches to the spinous process of the uppermost 4 thoracic vertebrae and the lower 2 cervical vertebrae

The semispinalis thoracis works with other back muscles—namely the longissimus thoracis, the iliocostalis thoracis, and the spinalis thoracis when performing its actions.

Semispinalis Cervicis

When the semispinalis cervicis muscle contracts, it extends or hyperextends your neck. If just one side is contracting, this results in lateral flexion of the neck—tilting your head to one side.

The semispinalis cervicis:

  • Starts at the transverse processes of your upper 5 or 6 thoracic vertebrae plus the articular processes of the 4th to 7th cervical vertebrae. An articular process is a small projection of bone arising from the back of the vertebra that connects with a similar process from the vertebra either directly above or below. In all, you have 4 articular processes per spinal bone. These articular processes make up the facet joints.
  • The other end of this muscle attaches to the spinous process of the 2nd through 5th cervical vertebrae.

In some types of laminoplasty surgery, the semispinalis cervicis may heal slowly.

Semispinalis Capitis

The semispinalis capitis extends and tilts the head to the same side on which the muscle is located and turns it to the opposite side. The semispinalis capitis works with the splenius muscle group and the semispinalis cervicis to perform its functions.

The semispinalis capitis spans about four to six segments of the upper thoracic and cervical spines.

  • The semispinalis capitis arises, or originates, from the tips of the transverse processes of the upper 6 or 7 thoracic spine, as well as the articular processes (these are the processes that make up the facet joints) of the 4th, 5th, 6th, and 7th cervical vertebrae.
  • Its fibers run up and in (technically called superomedially) to insert onto the bottom of the occipital bone, which is the bone at the lower part of the back of your skull, where it attaches between the superior and the inferior nuchal lines there.
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