11.4 Axial Muscles of the Abdominal Wall, and Thorax
3 min read•june 18, 2024
The , thoracic, and muscles form a dynamic system crucial for . These muscle groups work together to protect organs, support posture, and enable movement in daily activities and exercise.
Understanding how these muscles function is key to grasping their roles in breathing, organ support, and body mechanics. Their coordinated actions impact everything from maintaining continence to powering athletic performance and preventing injuries.
Abdominal Wall Muscles
Structure of abdominal muscles
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Outermost layer of abdominal muscles runs inferiorly and medially from lower ribs to and (midline raphe)
Compresses and supports abdominal viscera (organs), flexes and rotates trunk (sit-ups, twisting motions)
Middle layer of abdominal muscles runs perpendicular to external obliques, superiorly and medially from to lower ribs and
Compresses and supports abdominal viscera, flexes and rotates trunk in opposite direction of external obliques (stabilizes spine during rotational movements)
Innermost layer of abdominal muscles runs horizontally around the abdomen, attaching to lower ribs, iliac crest, and pubic bone
Compresses and supports abdominal viscera, stabilizes the spine and pelvis (acts like a corset)
Paired, vertical muscles on the anterior abdominal wall separated by the linea alba, attaches to and
Flexes the trunk (crunches), compresses abdominal viscera (increases intra-abdominal pressure)
These muscles collectively form the abdominal wall, which provides protection and support for internal organs
Thoracic Muscles and Breathing
Breathing mechanics of thoracic muscles
Dome-shaped muscle separating thoracic and abdominal cavities, attaches to lower ribs, sternum, and lumbar vertebrae
Contraction flattens the , increasing vertical dimension of ()
Relaxation allows the diaphragm to rise, decreasing vertical dimension of ()
Fibers run inferiorly and anteriorly from rib to rib
Contraction elevates the ribs, increasing anteroposterior and transverse dimensions of thoracic cavity (inhalation)
Fibers run inferiorly and posteriorly from rib to rib
Contraction depresses the ribs, decreasing anteroposterior and transverse dimensions of thoracic cavity (exhalation)
Breathing mechanism
Inhalation: Diaphragm contracts and flattens, external intercostals contract and elevate ribs, increasing thoracic cavity size and decreasing pressure, causing air to flow into lungs
Exhalation: Diaphragm relaxes and rises, internal intercostals contract and depress ribs, decreasing thoracic cavity size and increasing pressure, causing air to flow out of lungs
These muscles are collectively known as and play a crucial role in the mechanics of breathing within the
Pelvic Floor and Perineal Muscles
Pelvic vs perineal muscle functions
Pelvic floor muscles
Broad, thin muscle forming the floor of the pelvic cavity, attaches to pubic bone, ischial spine, and coccyx