Serratus Posterior Muscles: Function & Innervation

Instructor: Dan Washmuth

Dan has taught college Nutrition and Anatomy courses for over 5 years. He has a B.S. in Exercise Physiology from Furman University and a M.S. in Dietetics & Nutrition from Florida International University. He is a Registered Dietitian (RD) and a Certified Exercise Physiologist (EP-C)

How much do you know about the innervation and function of the serratus posterior muscles located in your back? If you answered ''not much,'' then you should definitely check out this lesson!

Serratus Posterior Muscles

How well are your serratus posterior muscles working? To find out, try this simple at home physical assessment test:

  1. Stand up with your arms hanging naturally at your sides
  2. Take a long, deep breath in
  3. Now blow all of that air out through your mouth
  4. Bend your back slightly backwards then come back to upright position
  5. Now turn your back to the right
  6. Now turn your back to the left

If you were able to complete all of these steps without much difficulty or pain, then your serratus posterior muscles are working pretty well!

The serratus posterior muscles are muscles that are located in the upper and lower parts of the back. These muscles actually consist of two different sections of muscles, which include:

  • Serratus posterior superior: a thin, four-sided muscle located in the upper back
  • Serratus posterior inferior: a thin muscle located in the lower back

This picture shows the serratus posterior inferior, which is located at both sides of the lower back. The serratus posterior superior is located under several muscles in the upper back.
serratus inferior

Serratus Posterior Muscles: Innervation

The serratus posterior muscles are innervated by several nerves from the ventral rami. The ventral rami are the nerves that make up the anterior divisions of the spinal nerve. For example, spinal nerves come out of each of the vertebra of the spinal column. Some nerves branch off posteriorly (to the back) while other nerves branch off to the anteriorly (to the front). The ventral rami are the nerves that branch off anteriorly. The following chart describes the specific nerves that innervate each section of the serratus posterior muscles.

Section of Serratus Posterior Muscles Innervating nerves
Serratus Posterior Superior Ventral rami of T1 - T5
Serratus Posterior Inferior Ventral rami of T9 - T12

The 'T' stands for thoracic, which means that these nerves are found in the thoracic region of the spinal column. The thoracic region of the spinal column is located in the back, between the base of the neck and the lower back. There are 12 total thoracic vertebrae.

The serratus posterior muscles are innervated from ventral rami nerves from the thoracic vertebrae.
vertebral column

Serratus Posterior Muscles: Function

The function of the serratus posterior muscles for each section, and the following chart describes the different functions of each section of the muscle (which are the same actions you performed during the physical assessment test at the beginning of the lesson).

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