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Serratus Posterior Inferior – Functional Anatomy

Serratus Posterior Inferior

Origin

The spinous processes of T11-L2

Insertion

the inferior border of the last four ribs, just lateral to the angle of the rib

Function

Its position indicates that it should extend and rotate the trunk, as well as assist in breathing, especially when breathing is forceful, or the trunk is contorted. It is, however, hard to find electromyographical studies that have determined when this muscle contracts.

Breathing muscles

Attachment Details

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

Serratus posterior inferior originates on T11-L2 and inserts on ribs 9-12, trapping the 9th and 10th thoracic vertebrae. There is a thin sheet of connective tissue that continues from the short bellies of the muscle on the rib to the supraspinous ligament over the spinous process.

Functional Considerations

Serratus posterior inferior produces pain in labored breathing, coughing, and vomiting. However, several studies conclude that it is not involved in breathing.

The two serratus posterior muscles are positioned in a layer between the intrinsic back muscles and the extrinsic back muscles. They strap over the spinal erectors, gathering the muscle bellies medially.

Anomalies, Etc.

A number of studies investigate the anomalies in this muscle. They all seem to conclude that there are no notable differences from one side to another. The only notable anomaly is the width of the aponeurotic strip that connects the muscle bellies to the spinous processes and ligaments.

Wikipedia entry for serratus posterior inferior

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