The abdominal muscles

Introduction

This comprehensive academic course provides an in-depth exploration of the abdominal muscles, a vital component of the human musculoskeletal system within the field of Myology. The focus is on presenting a clear, detailed, and rigorous understanding of the structure, function, and significance of these muscles in human physiology.

Anatomy of the Abdomen

Regions and Borders

The abdomen is the part of the body between the thorax and pelvis. It is bounded by the following:

1. Thoracic diaphragm (superior border)
2. Costal margins of the lower ribs (lateral borders)
3. The pelvic cavity (inferior border)
4. An imaginary line connecting the two anterior superior iliac spine (posterior borders)

Muscles of the Abdomen

The abdominal muscles can be divided into three groups:

1. External abdominal muscles
2. Internal abdominal muscles
3. Transversus abdominis

Each group will be discussed in detail, including their origins, insertions, actions, and innervation.

The External Abdominal Muscles

The external abdominal muscles consist of four layers:

1. Rectus abdominis
2. External oblique
3. Internal oblique
4. Transversus abdominis (transversely oriented muscle that sits deep to the other three muscles)

Rectus Abdominis

• Origin: The inferior surfaces of the 5th, 6th, and 7th costal cartilages, the xiphoid process, and the linea alba.
• Insertion: The linea alba in the pubic symphysis, but may also insert into the pubic tubercle or the inguinal ligament.
• Function: Flexion of the vertebral column, compression of the abdomen (as seen in sit-ups), and maintaining a firm abdominal wall.
• Innervation: The anterior rami of T7 to T12 spinal nerves via the intercostal nerves.

External Oblique Muscle

• Origin: The lower eight ribs (the costal margin, costal cartilage, and the adjacent part of the posterior aspect of the rib), the iliac crest, and the anterior superior spine of the ilium.
• Insertion: Linea alba, pubic tubercle, and the inguinal ligament.
• Function: Flexion, lateral flexion (bending the trunk to either side), and rotation of the vertebral column. Also involved in forced expiration.
• Innervation: The anterior rami of T7 to T12 spinal nerves via the intercostal nerves and the subcostal nerve.

Internal Oblique Muscle

• Origin: The iliac crest, upper three or four ribs (anterior surface), and the linea alba inferiorly.
• Insertion: The linea alba superiorly, the pubis and pecten pubis inferiorly, and the iliopubic eminence laterally.
• Function: Flexion, lateral flexion (bending the trunk to either side), and rotation of the vertebral column. Also involved in forced expiration.
• Innervation: The anterior rami of T12 to L3 spinal nerves via the subcostal nerve, intercostal nerves, and iliohypogastric and ilioinguinal nerves.

The Internal Abdominal Muscles

The internal abdominal muscles include three layers:

1. External layer (includes the psoas major and iliacus)
2. Middle layer (contains the transversus abdominis, psoas minor, and quadratus lumborum)
3. Anterior layer (consists of the rectus abdominis and pyramidalis)

The Transversus Abdominis

• Origin: Lateral part of the lower six costal cartilages, the lumbar fascia on the inner side of the posterior surfaces of the lower six vertebrae (transverse processes), the lumbar transversalis fascia, and the inguinal ligament.
• Insertion: The linea alba in the pubic symphysis.
• Function: Compresses and supports the abdominal contents, provides lateral stability to the vertebral column, and assists with respiration by increasing the intra-abdominal pressure during expiration.
• Innervation: The anterior rami of T6 to L1 spinal nerves via the intercostal nerves.

Clinical Relevance

Understanding the anatomy and function of the abdominal muscles is crucial for healthcare professionals, physical therapists, personal trainers, and athletes. Common conditions related to these muscles include hernias, strains, and sports injuries.

Conclusion

This course has provided a comprehensive exploration of the abdominal muscles, delving into their anatomy, function, innervation, and clinical relevance within the field of Myology.