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.