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Spinalis Thoracis Muscle
Muscular System

Spinalis Thoracis Muscle

Musculus spinalis thoracis

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Quick Facts

Origin: Spinous processes of T11-L3 vertebrae.

Insertion: Spinous processes of T2-T8 vertebrae.

Action: Extends and laterally flexes trunk.

Innervation: Posterior rami of thoracic and upper lumbar nerves.

Arterial Supply: Dorsal branches of posterior intercostal, subcostal, and upper lumbar arteries.

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Origin

The spinalis thoracis muscle originates from the spinous processes of the eleventh thoracic to third lumbar vertebrae. There can be variations between individuals regarding the origin sites for the spinalis thoracis muscle (Tubbs, Shoja and Loukas, 2016).

Insertion

The fibers of the spinalis thoracis muscle travel superiorly along the upper back region and insert onto the spinous processes of the second to eighth thoracic vertebrae. There can be variations between individuals regarding the insertion sites for the spinalis thoracis muscle (Tubbs, Shoja and Loukas, 2016).

Key Features & Anatomical Relations

Overall, the spinalis muscles are the most medial of the erector spinae. They are intrinsic muscles of the back and are found along the back and posterior neck regions. They are long, flat skeletal muscles that are composed of two parts:

- spinalis colli, which is the superior portion;

- spinalis thoracis, which is the inferior portion.

In some individuals, there is a third part, known as the spinalis capitis, which, blends with the semispinalis capitis muscle (Greiner, Bedford and Walker, 2004).

The spinalis muscles are located:

- superficial to the semispinalis and multifidus muscles;

- deep to the splenius capitis, splenius colli, trapezius, latissimus dorsi, and serratus posterior inferior muscles, and the thoracolumbar fascia;

- medial to the longissimus muscle.

Actions

The spinalis thoracis muscle is involved in multiple actions:

- during unilateral contraction, it laterally flexes the trunk to the same side;

- during bilateral contraction, it extends the trunk (Standring, 2016).

References

Greiner, T. M., Bedford, M. E. and Walker, R. A. (2004) 'Variability in the human M. spinalis capitis and cervicis: frequencies and definitions', Annals of Anatomy - Anatomischer Anzeiger, 186(2), pp. 185-191.

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.

Tubbs, R. S., Shoja, M. M. and Loukas, M. (2016) Bergman's Comprehensive Encyclopedia of Human Anatomic Variation. Wiley.

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