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Serratus posterior inferior muscle

Origins, insertions, innervation and function of the serratus posterior inferior muscle.

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Hey there everyone! It’s Matt from Kenhub, and in this tutorial, we will discuss the serratus posterior inferior muscle. The serratus posterior muscles are two thin, superficial back muscles which lie above the intrinsic back musculature. They are also referred to as spinal costal muscles. The serratus posterior muscles are comprised of the serratus posterior superior muscle and the serratus posterior inferior muscle. In this short tutorial, we will focus on the serratus posterior inferior muscle or musculus serratus posterior inferior.

The serratus posterior inferior muscle originates from the spinous processes of the T11 to T12 thoracic vertebrae and has its insertion on the four lower ribs. Both muscles are known to be among the secondary back muscles, meaning that they migrated to the back in the course of embryogenesis. Therefore, their nerve supply comes from the posterior branches of the spinal nerves, the intercostal nerves.

The serratus posterior muscles contribute to the movement and stabilization of the vertebral column and the thorax. Furthermore, the activation on both sides extends the thoracic vertebral column while a unilateral contraction rotates it to the opposite side. The serratus posterior inferior helps during expiration by depressing the ribs making it an accessory muscle of expiration. This muscle can also extend the spine in a bilateral contraction and rotates the spine in unilateral contraction.

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