Serratus Posterior Superior – Functional Anatomy

Serratus posterior superior is a thin, flat muscle in the upper back. It anchors on the spine and assists in the breathing process by lifting the ribs. It is deep to the extrinsic back muscles but straps over the erectors and other intrinsic back muscles.

Anatomy Overview

This muscle is the most superficial of the intrinsic back muscles and straps across the erectors, levator costae, and intrinsic spine muscles.

This muscle acts as a 5th scalene. It has similar attachments. Likewise, it elevates the ribs for inhalation. It is especially active when the person is bent forward, as when working on a laptop while reclining on a couch.

Serratus posterior superior attaches to C6-T3 and inserts on ribs 2-5, trapping the 2nd and 3rd thoracic vertebrae. A thin sheet of connective tissue attaches along the mid-line of the spine. The width of this aponeurosis varies significantly among dissections but tends to be a much larger part of the structure than is usually illustrated.

Its strongest insertion is along the superior aspects of the 2nd through 5th ribs near the lateral angle. In dissections, it clearly feathers into the fascia between the ribs so that it has the shape of a rhomboid rather than the finger-like bellies that are commonly illustrated.

Basics of Attachment and Function

Origin – nuchal ligament from about C6 and along the supraspinous ligament and spinous processes from C7 to T2 or T3.

Insertion – superior aspect of ribs 2-5, just lateral to the angle of the rib

Function – elevation of the ribs, assists in inhalation

Nerve – T1-T4

Assisting in Breathing

Breathing muscles can be divided into three groups:

  • The diaphragm is considered as the primary breathing muscle.
  • Several muscles assist breathing by pulling on the rib cage to reshape and expand lung capacity.
  • Extrinsic back and extrinsic chest muscles lift the shoulder girdle and ribs during labored breathing.

This is one of the muscles that assist in the breathing process. Basically, these muscles act to expand lung capacity by pulling ribs. In most cases, they should be most active when the diaphragm is unable to engage. This might occur when we are bent forward while working at a desk, curled forward on a couch, or putting on our shoes.

Because of our sedentary lifestyle, these muscles tend to be over-used when we are breathing quietly. We become trained to use them, even when the diaphragm can do the job.

These muscles include:

  • Scalenes
  • Serratus posterior superior
  • Serratus posterior inferior
  • Intercostals

Lifestyles that involve a great deal of desk work, especially computer work, create an increasing strain on serratus posterior superior. In this posture, the scapula presses into the ribs. Consequently, this aggravates the serratus posterior superior with compression and restricts breathing. The lower ribs press forward into the abdomen. Additionally, the small serratus posterior superior is working harder to lift the ribs and assist in breathing. The illustration shown is from a healthier posture. As the shoulder elevates, the scapula, hinged on the collar bone, moves medially. As a result, the vertebral border digs into the underlying muscle as the arm moves to, for example, use the mouse.

Wikipedia entry for serratus posterior superior.

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