Muscles of the abdomen:thorax

Muscles of the Abdomen and Thorax

Muscles of the Abdomen

  • Anterolateral Abdominal Wall

    • Consists of four pairs of muscles converging at the anterior midline:

      1. External Obliques

      2. Internal Obliques

      3. Transversus Abdominis

      4. Rectus Abdominis

    • Each muscle group has specific traits and functions as highlighted in the following table:

Table 1: Overview of Abdominal Muscles

  • Movement:

    • Twisting at waist; bending to the side (External & Internal Obliques)

    • Squeezing abdomen during forceful exhalations, defecation, urination, and childbirth (Transversus Abdominis)

    • Sitting up; bending to the side (Rectus Abdominis)

  • Target Motion Direction:

    • External Obliques: Vertebral column lateral flexion

    • Internal Obliques: Compression of abdominal cavity

    • Transversus Abdominis: Flexion of vertebral column

    • Rectus Abdominis: Lateral flexion of vertebral column

  • Prime Mover:

    • External Obliques: External obliques, Internal obliques

    • Transversus Abdominis: Transversus abdominis

    • Rectus Abdominis: Rectus abdominis, Quadratus lumborum

  • Origin/Inserts:

    • External Obliques: Ribs 5-12; iliac crest

    • Internal Obliques: Ilium; ribs 7-10

    • Transversus Abdominis: Ilium; ribs 5-10

    • Rectus Abdominis: Pubis; ribs 5-7 (via the costal cartilage)

Muscle Layers

  • External Oblique: Superficial layer, extends inferiorly and medially.

  • Internal Oblique: Middle layer, extending superiorly and medially.

  • Transversus Abdominis: Deepest layer, arranged transversely.

  • Linea Alba: Fibrous band joining at the anterior midline enclosing rectus abdominis.

  • Rectus Abdominis: Long muscles segmented by collagen bands, contributing to "six-pack abs."

Posterior Abdominal Wall

  • Formed by lumbar vertebrae, iliac bones, psoas major, iliacus, and quadratus lumborum.

  • Essential for posture and core stability.

Muscles of the Thorax

  • Role in Breathing: Alter thoracic cavity size during inhalation and exhalation.

Table 2: Overview of Thoracic Muscles

  • Movement:

    • Inhalation/Exhalation: Compression and expansion of thoracic cavity.

  • Prime Mover:

    • Diaphragm for inhalation, External and Internal Intercostals for both inhalation and exhalation.

  • Origin/Inserts:

    • Diaphragm: Originates from sternum, ribs 6-12, lumbar vertebrae; inserts into central tendon.

    • Intercostals: External (superior to ribs), Internal (inferior to ribs).

Diaphragm

  • Dome-shaped muscle separating thoracic and abdominal cavities.

  • Critical for breathing by modifying thoracic cavity volume.

  • Works with abdominal muscles for functions like defecation and urination (Valsalva maneuver).

Anatomy of the Diaphragm

  • Central Tendon: Fuses with pericardial sac and pleura.

  • Openings in Diaphragm:

    • Caval Opening: For inferior vena cava.

    • Esophageal Hiatus: For esophagus and nerves.

    • Aortic Hiatus: For aorta, thoracic duct, and azygous vein.

Intercostal Muscles

  • Three sets (External, Internal, Innermost) aiding in breathing by changing rib cage dimensions.

  • External Intercostals: Aid in inhalation by expanding rib cage.

  • Internal Intercostals: Assist in exhalation by constricting rib cage.

  • Innermost Intercostals: Work synergistically with internal intercostals for effective exhalation.