A Body in Motion  The muscular system allows us to move, flex and contort our bodies. Practicing yoga, as pictured here, is a good example of the voluntary use of the muscular system. (credit: Dmitry Yanchylenko; openstax anatomy and physiology https://openstax.org/books/anatomy-and-physiology/pages/11-introduction)

Learning Objectives

By the end of this section, you will be able to:

Identify, locate, and describe the origin, insertion and function of four abdominal muscles.

The following four muscles are described from superficial to deep:

1. External oblique

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         This broad, flat muscle covers much of the lateral trunk.  Its fibers run downwards and forwards (toward the midline) It can be described as running inferiorly and medially (think of hands in your pockets).

lower eight ribs (ribs 5-12)

iliac crest of the pelvis and the pubic tubercle as well as a broad aponeurosis of the lower anterior abdominal wall (An aponeurosis is a sheet-like layer of dense connective tissue joining one muscle to another or with bone.).

Contraction of both (i.e., right and left) obliques compresses the abdomen (you bend forward).  Contractions of one side only bends the vertebral column laterally (lateral flexion of the vertebral column).

2. Internal oblique

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        This is a broad, sheet-like muscle, located deep to the external oblique. Smaller than the external oblique, fibers of this muscle slope upwards and forwards. It can be described as running superiorly and medially (think of left hand on heart).

the anterior part of the iliac crest of the pelvis

onto ribs 10-12 and an aponeurosis of the upper anterior abdominal wall

This muscle causes abdominal compression when both right and left contract.  Contraction of one side only bends the vertebral column laterally.

This muscle causes abdominal compression when both right and left contract.  Contraction of one side only bends the vertebral column laterally.

3. Rectus abdominis

This shows two long strips of vertical rectus abdominis muscle.
Visible Body

         This narrow muscle runs vertically on either side of the abdominal midline. It can be referred to as your ‘six pack‘. It consists of two parallel muscles separated by a connective tissue (linea alba).  

pubic crest and symphysis

xiphoid process of the sternum and costal cartilages of ribs 5-7

It flexes the vertebral column causing abdominal compression. It pulls the pubic symphysis and sternum toward each other when you ‘take a bow’.

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4. Transversus abdominis

The innermost of the muscles of the abdominal wall whose fibers run almost horizontally around the abdomen from front to back.  Locate the origin and insertion sites on the diagram to the right.

costal cartilages of ribs 7-12, thoracolumbar fascia, iliac crests and inguinal ligaments

xiphoid process of the sternum and the pubis/pubic crest and linea alba/aponeurosis

abdominal compression causing expiration, coughing and defecation

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