Muscles of the Abdominal Wall and Structures

Overview

The abdominal wall is composed of several layers of muscle that provide structural support, protect internal organs, and assist in movements such as flexion, rotation, and compression of the trunk. These muscles also play a role in respiration and maintaining intra-abdominal pressure.

• Rectus abdominis: A long, flat muscle extending along the front of the abdomen; responsible for flexing the vertebral column and compressing abdominal contents.

• Linea alba: A fibrous structure running down the midline of the abdomen, formed by the fusion of the aponeuroses of the abdominal muscles.

• Rectus sheath: A sheath formed by the aponeuroses of the abdominal muscles that encloses the rectus abdominis.

• Tendinous intersections: Transverse fibrous bands that segment the rectus abdominis, giving the 'six-pack' appearance.

• External abdominal oblique: The most superficial of the lateral abdominal muscles; fibers run downward and medially. Functions in trunk rotation and lateral flexion.

• Internal abdominal oblique: Lies beneath the external oblique; fibers run upward and medially. Assists in trunk rotation and lateral flexion.

• Transverse abdominis: The deepest abdominal muscle; fibers run horizontally. Compresses abdominal contents and stabilizes the trunk.

Key Functions

• Protection of abdominal organs

• Movement and stabilization of the trunk

• Assistance in forced expiration and coughing

Muscles of Breathing

Muscles of Quiet Breathing

Quiet breathing, or normal respiration at rest, primarily involves the diaphragm and external intercostal muscles.

• Diaphragm: The main muscle of inspiration; contracts to increase thoracic volume and draw air into the lungs.

• External intercostals: Located between the ribs; elevate the ribs during inspiration, expanding the thoracic cavity.

Muscles of Forced Inspiration

During deep or labored breathing, additional muscles assist in expanding the thoracic cavity.

• Sternocleidomastoid: Elevates the sternum and clavicle, increasing thoracic volume.

• Scalenes: Elevate the first two ribs, aiding in deep inspiration.

• Pectoralis minor: Elevates ribs during forced inspiration.

• Diaphragm: Continues to contract more forcefully.

• External intercostals: Continue to assist in rib elevation.

Muscles of Forced Expiration

Forced expiration, such as during vigorous exercise or coughing, involves active contraction of abdominal and intercostal muscles.

• Internal intercostals: Depress the ribs, reducing thoracic volume.

• Rectus abdominis: Compresses abdominal contents, pushing the diaphragm upward.

• External abdominal oblique: Compresses the abdomen, aiding in expiration.

• Diaphragm: Relaxes and is pushed upward by abdominal muscles.

Muscles of the Back

Superficial Muscles of the Back

These muscles are primarily responsible for movements of the upper limb and stabilization of the scapula.

• Trapezius: Large, superficial muscle that moves the scapula and supports arm movements.

• Latissimus dorsi: Broad muscle of the lower back; extends, adducts, and medially rotates the arm.

• Levator scapulae: Elevates the scapula.

• Teres major: Assists in arm adduction and medial rotation.

Muscles of the Deep Back

Deep back muscles are involved in maintaining posture and controlling movements of the vertebral column.

• Erector spinae (on diagrams only): A group of muscles running along the spine; responsible for extension and lateral flexion of the vertebral column.

• Rhomboids (major and minor): Retract and stabilize the scapula.

• Serratus posterior inferior (on diagrams only): Assists in depressing the lower ribs during forced expiration.

Table: Summary of Muscle Groups and Functions

Additional info:

• The rectus sheath and linea alba are important anatomical landmarks for abdominal surgeries.

• Muscles of respiration work together to change thoracic volume, which drives airflow according to Boyle's Law: .

• Back muscles are often grouped as superficial (extrinsic) and deep (intrinsic) based on their location and function.