Intrinsic Back Muscles

Usual disclaimer, all drawings are done by me, while I try to remain as accurate as possible, I am only a student. There are natural human variations and differences between textbooks. That being said, I hope my illustrations can be of some help.

Before reading about the Intrinsic Back muscles, take a chance to check out this blog by Dr. Throckmorton about ‘How to Succeed in Medical Gross Anatomy‘.

Now there are quite a few intrinsic back muscles. I did not draw them all, but here are some of the ones that are easiest to see in a dissection.

The three muscles: Iliocostalis, Longissimus, and Spinalis are collectively known as the Erector Spinae

The Intrinsic Back Muscles are deep to the Extrinsic Back Muscles, but they are separated into 3 categories based on their depth to one another.

Don’t get discouraged by how many of them there are. Their names give away their location. If it ends with capitis, it attaches to the skull. If it ends with cervicis, it attaches to the cervical vertebrae. If it ends in thoracis, it attaches to the thoracic vertebrae and ribs. If it ends in lumborum, it attaches to the lumbar spine. See! It makes sense.

Now, last but not least is the difference between Extrinsic and Intrinsic Back Muscles. It took me a bit to understand this one. See it has to do with where the muscles develop when we are all tadpoles in our mom’s bellies.

The Intrinsic Back Muscles arise from something called with Epimere of the myotome. While the Extrinsic Back Muscles arise from the Hypomere of the myotome.

This represents a cut section of a developing embryo.

Because of how these sections develop it effects how the different muscle groups are innervated and what they do.

 

References:

Netter, F. H. (2019). Atlas of human anatomy (7th ed.). Philadelphia, PA: Elsevier.

Moore, K. L., Agur, A. M., & Dalley, A. F. (2015). Essential clinical anatomy(5th ed.). Philadelphia: Lippincott Williams & Wilkins.

 

 

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