trunk 2

Muscles of the Trunk

• Includes abdominal and back muscles, diaphragm, and intercostal muscles.

• Major arteries and veins enter/exit heart in trunk.

Abdominal Muscles

• External Obliques:
    - Origin: Ribs 5-12
    - Insertion: Iliac crest & linea alba.
    - Action: Trunk flexion, lateral flexion, opposite side rotation.

• Internal Obliques:
    - Origin: Iliac crest & inguinal ligament.
    - Insertion: Cartilage of ribs 7-10.
    - Action: Trunk flexion, lateral flexion, same side rotation.

• Transverse Abdominis:
    - Deepest abdominal muscle.
    - Muscle fibers run transversely.
    - Functions: Compress abdomen, stabilize spine/pelvis, increase intra-abdominal pressure.

• Rectus Abdominis:
    - Origin: Pubic crest & symphysis.
    - Insertion: Xiphoid process and cartilage of ribs 5-7.
    - Action: Trunk flexion (six-pack appearance).

Back Muscles

• Quadratus Lumborum:
    - Origin: Iliac crest.
    - Insertion: Inferior border of lower ribs, lumbar vertebrae processes.
    - Action: Trunk extension and lateral flexion.

• Erector Spinae:
    - Group of muscles along vertebral column.
    - Action: Trunk extension and lateral flexion.

Breathing Muscles

• Diaphragm:
    - Dome-shaped muscle beneath lungs.
    - Primary breathing regulator, contracts to increase thoracic cavity space.

• Intercostal Muscles:
    - External intercostals elevate ribs during inhalation.
    - Internal intercostals depress ribs during forced exhalation.

Blood Vessels of the Trunk

• Arteries:
    - Aorta: Exits heart, divided into ascending, arch, and descending aorta.
    - Common iliac arteries supply pelvic organs and lower limbs.

• Veins:
    - Inferior vena cava drains blood from lower body.
    - Superior vena cava drains blood from upper body.
    - Both empty into right atrium.