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Anterolateral Abdominal Wall Muscles Anatomy
Anterolateral Abdominal Wall Muscles Anatomy
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The abdominal wall surrounds and protects the organs in your abdomen, supports movements of your trunk, and helps maintain posture and stability.
Because the abdominal wall has to be both strong and flexible, its muscles work together in coordinated ways to allow bending, twisting, breathing, and maintaining internal pressure.
Your abdominal muscles are located in the front and sides of your trunk, stretching from the bottom of your ribcage down to your pelvis.
These muscles are grouped into
Vertical muscles located near the midline.
Flat muscles located on the sides.
Together with your back muscles, they form your core, which plays a key role in balance, stability, and protection of the spine.
Location and General Function
Location and General Function
Your abdominal muscles are strong bands of muscle that form the front and side walls of your abdomen (the area between your ribs and your pelvis). These muscles are part of your body’s core, working with the back muscles to protect the spine, maintain balance, and support good posture.
Main functions of the abdominal muscles include:
Supporting and stabilizing the trunk during movement.
Holding organs in place and protecting them from injury.
Controlling internal abdominal pressure (which helps with breathing, bowel movements, urination, vomiting, and childbirth).
Aiding trunk movement, allowing you to bend, twist, and maintain posture.
The Five Main Abdominal Muscles
The Five Main Abdominal Muscles
There are five pairs of muscles that make up the abdominal wall - two vertical muscles (Rectus Abdominis and Pyramidalis) near the midline and three flat muscles (External Oblique, Internal Oblique, and Transversus Abdominis) on the sides. Together, they form a flexible yet strong structure that supports both movement and protection of internal organs.
Rectus Abdominis
The rectus abdominis is a long, paired muscle running vertically along the anterior abdominal wall. It flexes the trunk, compresses the abdominal contents, and stabilizes the pelvis during movement.
Origin: Pubic crest and pubic symphysis.
Insertion: Xiphoid process and costal cartilages of ribs 5–7.
Innervation: Thoracoabdominal nerves (T7–T11).
The muscle is divided by fibrous bands called tendinous intersections, which create the appearance of a “six-pack” in well-developed individuals.
The two muscles are separated by the linea alba and bordered on the sides by the linea semilunaris.
Pyramidalis
The pyramidalis is a small triangular muscle located in front of the rectus abdominis, near the lower abdomen. It tenses the linea alba.
The Pyramidalis muscle is a variable muscle; it's absent in about 20% of people.
Origin: Pubic crest and pubic symphysis.
Insertion: Linea alba.
Innervation: Subcostal nerve (T12).
Flat Muscles
The lateral abdominal wall is made up of three flat muscles layered on top of each other. Their fibers run in different directions, which gives the abdominal wall both strength and flexibility, similar to how multiple layers of plywood reinforce each other. These muscles help control movement, stability, and internal pressure. They also play major roles in protecting abdominal organs.
External Oblique
The external oblique covers the side of your abdomen from the ribs down to the pelvis. Its fibers run downward and toward the midline, the same direction as your fingers if you place your hands in your pockets.
This muscle has a large, sheet-like tendon (aponeurosis) that contributes to the anterior rectus sheath.
Its main job is trunk rotation (to the opposite side - if the right external oblique contracts, it rotates the trunk to the left), bending sideways, and bending the body forward when both sides contract. The external oblique also supports abdominal pressure during breathing, coughing, and lifting.
Origin: Ribs 5-12.
Insertion: Iliac crest and pubic tubercle.
Innervation: Thoracoabdominal nerves (T7–T11) and subcostal nerve (T12).
Internal Oblique
The internal oblique lies deep to the external oblique. Its fibers run upward and inward, opposite the external oblique.
Its aponeurosis contributes to both the anterior and posterior portions of the rectus sheath, depending on its height relative to the arcuate line. This muscle shares functions with both the external oblique and transversus abdominis, making it a key “middle layer” of the abdominal wall.
Its main job is trunk rotation (to the same side - if the right internal oblique contracts, it rotates the trunk to the right), bending sideways, and supporting the lumbar spine.
Origin: Iliac crest, inguinal ligament, and thoracolumbar fascia.
Insertion: Ribs 10–12 and the linea alba.
Innervation: Thoracoabdominal nerves (T7–T11), subcostal nerve (T12), and branches from the lumbar plexus.
Quick Reference Table: Muscle Name, Origin, Insertion & Innervation
Ready for download! Your muscle cheat sheet is here. Save it for later, study on the go, and review the essentials anytime.
Transversus Abdominis
The transversus abdominis is the deepest of the abdominal wall muscles, lying beneath both oblique muscles. Its fibers run horizontally, like a belt or corset wrapping around the abdomen.
It forms the deepest part of the rectus sheath (posterior layer above the arcuate line) and connects strongly to the thoracolumbar fascia, directly linking it to lower-back stability.
Its main job is maintaining internal abdominal pressure, stabilizing the pelvis and supporting internal organs, and forcefully exhaling by pushing abdominal contents upward toward the diaphragm. It also engages before arm and leg movement, protecting the lower back.
Origin: Costal cartilages 7–12, iliac crest, inguinal ligament, and thoracolumbar fascia.
Insertion: Linea alba and pubic crest.
Innervation: Thoracoabdominal nerves (T7–T11), subcostal nerve (T12), and lumbar plexus branches.
Linea Alba
Linea Alba
The linea alba is a vertical line of tough connective tissue in the midline. It's formed where the flat muscles’ aponeuroses meet and serves as an important landmark, dividing the rectus abdominis into left and right halves.
The linea alba is a vertical line of tough connective tissue in the midline. It's formed where the flat muscles’ aponeuroses meet and serves as an important landmark, dividing the rectus abdominis into left and right halves.
Need a recap? Take a look at the Anterolateral Abdominal Wall Muscles anatomy notes here.
Need a recap? Take a look at the Anterolateral Abdominal Wall Muscles anatomy notes here.
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References
References
Gray, H. (2009). Anatomy of the human body, part 2 (LibriVox Volunteers, Narr.) [Audiobook]. LibriVox. https://librivox.org/anatomy-of-the-human-body-part-2-by-henry-gray/ (Original work published 1858)
J Gordon Betts, Desaix, P., Johnson, E., Johnson, J. E., Korol, O., Kruse, D., Poe, B., Wise, J., Womble, M. D., & Young, K. A. (2013). Anatomy & physiology. Openstax College, Rice University. https://openstax.org/details/books/anatomy-and-physiology
Based on OpenStax, Anatomy and Physiology (2013), licensed under CC BY 4.0.
Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.
Content paraphrased; adaptations were made.
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