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Semispinalis muscles

German: Musculi semispinales

1 Definition

The Semispinalis muscles are skeletal muscles of the muscles of the back. They form part of the medial tract of the erector spinae muscles.

2 Structure and devolution

The semispinalis muscles are present in the region of the head, the cervical and thoracic spine. The originate in the transverse process (or homologous areas) and mostly insert 6-7 vertebral levels above on the spinous process or the occipital bone.

For better orientation, you can differentiate between three groups of muscles:

  • Semispinalis capitis muscle
  • Semispinalis cervicis muscle
  • Semispinalis thoracis muscle

2.1 Semispinalis capitis muscle

The muscle groups of the semispinalis capitis muscle originate in the articular processes of the 6th thoracic vertebra to the 3rd cervical vertebra. They insert in the medial area of the occipital bone between the superior and inferior nuchal line.

2.2 Semispinalis cervicis muscle

The origins of the semispinalis cervicis muscle range from the 7th to the 2nd thoracic vertebra, the corresponding insertions from the 6th to the 2nd cervical vertebra.

2.3 Semispinalis thoracis muscle

The origin surfaces of the semispinalis thoracis muscle lie on the transverse processes of the 12th to 7th thoracic vertebrae. The corresponding insertion areas range from the 4th thoracic vertebra to the 6th cervical vertebra.

3 Innervation

The innervation of the semispinalis muscles is provided by the medial branches of the posterior branches (Rami posteriores) of the corresponding segmental spinal nerves. Individual lateral branches of the Rami posteriores add to the semispinalis capitis muscle.

4 Function

The semispinalis capitis muscle turns the head to the opposite side with an unilateral contraction. With bilateral contraction, it causes dorsal flexion (extension) of the head.

The semispinalis cervicis and thoracis muscles turn the corresponding section of the spinal column to the opposite site with a unilateral contraction, and lateral flexion can be observed on the same side. With bilateral contraction, they assist in extension.

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