Lecture 24: Muscles of the Abdominal Pelvic Cavity

Learning Objectives

• Identify muscular boundaries of the abdominal pelvic cavity
• Understand the attachments, innervation, and function of these muscles
• Describe the location and organization of these boundaries
• Recognize the general functions of the "muscles of the container"

The Container

• Formed by a muscular roof, walls, and floor
• Spans from inferior thoracic aperture to the lesser or true pelvis

Osteological Boundaries

• Inferior Thoracic Aperture:
  • Anterior: Xiphoid process
  • Anterolateral: Costal margin (ribs 8–10)
  • Posterolateral: Floating ribs (11 and 12)
  • Posterior: T12 thoracic vertebra
• Lesser or True Pelvis:
  • Located inferior to the pelvic inlet
  • Bordered by the sacrum, ischium, and pubis

Muscular Boundaries of the Abdominal Pelvic Cavity

• Respiratory Diaphragm (roof)
• Anterolateral Abdominal Wall (walls)
• Pelvic Diaphragm (floor)

Functions of Muscles

• Increase intra-abdominal pressure
  • Aids in expiration, expulsion of fluids, feces, and childbirth

Respiratory Diaphragm

• Separates thoracic cavity from abdominal pelvic cavity
• Attachments: Xiphoid process, costal margin, floating ribs, T12, lumbar vertebrae
• Central tendon and muscular parts (sternal, costal, lumbar)
• Openings (apertures):
  • Caval Opening (T8): Inferior vena cava passage
  • Esophageal Hiatus (T10): Esophagus passage
  • Aortic Hiatus (T12): Aorta passage
• Innervation: Phrenic nerve (C3, C4, C5)

Anterolateral Abdominal Wall

• Comprised of:
  • External Oblique
  • Internal Oblique
  • Transversus Abdominis
  • Rectus Abdominis
• Functions:
  • Support and protect viscera
  • Aid in trunk movements
  • Increase intra-abdominal pressure
• Rectus Sheath:
  • Encloses rectus abdominis
  • Contributions from the aponeuroses of flat muscles

Pelvic Diaphragm

• Located within the lesser pelvis
• Muscles:
  • Coccygeus (Ischiococcygeus)
  • Levator Ani (iliococcygeus, pubococcygeus, puborectalis)
• Functions:
  • Support visceral organs
  • Maintain urinary and fecal continence
  • Active contraction increases support during increased intra-abdominal pressure

Summary

• Review the muscular boundaries, their attachments, innervation, and general functions
• Understand the importance of intra-abdominal pressure and its role in bodily functions

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Practice

• Identify structures on provided diagrams or models
• Be prepared for lab assessments

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Note: Review additional resources for anatomical identification and further clarification on muscular functions.