What are the five pairs of muscles in the anterior abdominal wall?

The anterior abdominal wall consists of five paired muscles: three flat muscles (external oblique, internal oblique, transversus abdominis) and two vertical muscles (rectus abdominis, pyramidalis). The flat muscles form aponeuroses that enclose the rectus abdominis within the rectus sheath.

What is the main function of the rectus abdominis muscle?

The rectus abdominis primarily flexes the trunk (e.g., during sit-ups). It is a vertical muscle enclosed in the rectus sheath and features tendinous intersections that give it a segmented appearance.

How do the external and internal oblique muscles differ in fiber direction?

Their fiber directions are perpendicular. The external oblique fibers run downward, forward, and medially (like hands in pockets), while the internal oblique fibers run upward and medially at a right angle. This arrangement enables trunk rotation and lateral flexion.

What is the conjoint tendon and why is it important?

The conjoint tendon (falx inguinalis) is formed by the fused lower aponeurotic fibers of the internal oblique and transversus abdominis. It inserts on the pubic crest and pecten pubis, providing crucial support to the posterior wall of the inguinal canal.

What is the cremaster muscle and what does it do?

The cremaster muscle originates from lower fibers of the internal oblique and forms loops around the spermatic cord and testis. Its main functions are to elevate the testis (e.g., in the cremasteric reflex) and aid in thermoregulation.

What are the general functions of the anterior abdominal muscles?

These muscles serve three key roles: support and protection of abdominal viscera, compression to aid in forced expiration, defecation, and childbirth, and movement including trunk flexion, lateral flexion, and rotation.

Is the pyramidalis muscle always present?

No, the pyramidalis is absent in about 20% of individuals. When present, it originates from the pubis and inserts into the linea alba, functioning to tense this midline structure.

Abdominal Wall Muscles – Obliques, Transversus & Rectus

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