Rectus Abdominis: Anatomy, Structure, and Vascular Supply
The rectus abdominis is a prominent, long, flat muscle that spans the entire length of the front of the abdomen. Commonly recognized for its role in core stability and movement, this muscle is split into two parallel halves, separated down the center by a fibrous structure known as the linea alba.
Unlike many other muscles that exist as a single continuous unit, the rectus abdominis is subdivided by tendinous intersections (intersectiones tendineae). These connective tissue bands divide the muscle into a series of smaller muscle bellies. When the muscle tenses, it expands between these intersections, creating the characteristic segmented appearance of the abdominal wall.
[ไม่มีภาพประกอบ]Key Facts
- Location: Extends along the full length of the anterior abdomen.
- Structure: Divided by the linea alba and segmented by tendinous intersections.
- Thickness: Typically 10 mm, reaching up to 20 mm in athletes.
- Volume: Ranges from 300 cm³ in non-active individuals to 500 cm³ in athletes.
- Innervation: Supplied by the T7-T11 thoraco-abdominal nerves.
Physical Dimensions and Volume
The size of the rectus abdominis varies significantly based on an individual's activity level. In the general population, the muscle is typically around 10 mm thick. However, in athletes, this thickness can double, reaching up to 20 mm.
Muscle volume also reflects these differences in physical conditioning. Non-active individuals generally possess a muscle volume of approximately 300 cm³, whereas athletes often exhibit a volume of around 500 cm³.
Anatomical Attachments and Variations
The upper portion of the rectus abdominis is primarily attached to the cartilage of the fifth rib. In many cases, some fibers of insertion extend directly into the anterior extremity of the rib itself.
Anatomical Variations
Human anatomy often presents variations. The sternalis muscle is one such example, which may appear as a variant form of either the pectoralis major or the rectus abdominis. Additionally, some fibers may occasionally connect to the side of the xiphoid process or the costoxiphoid ligaments.
Blood and Nerve Supply
The rectus abdominis relies on a complex network of arteries and nerves to maintain function and viability.
Vascular Anatomy
Blood is supplied to the muscle through three primary sources:
- Inferior epigastric artery and vein: These run superiorly on the posterior surface of the muscle, entering the rectus fascia at the arcuate line to serve the lower region.
- Superior epigastric artery: A terminal branch of the internal thoracic artery that provides blood to the upper portion of the muscle.
- Intercostal arteries: Numerous small segmental contributions are provided by the lower six intercostal arteries.
Innervation and Sensation
The muscle is innervated by thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. These nerves pierce the anterior layer of the rectus sheath to reach the muscle. Sensory supply to the area is provided by the 7-12 thoracic nerves.
Summary of Rectus Abdominis Characteristics
| Feature | Non-Active Individual | Athlete |
|---|---|---|
| Typical Thickness | 10 mm | Up to 20 mm |
| Typical Volume | 300 cm³ | 500 cm³ |
| Primary Nerve Supply | T7-T11 Thoraco-abdominal nerves | |
| Primary Blood Supply | Superior and Inferior Epigastric Arteries |
Frequently Asked Questions
What is the linea alba?
The linea alba is the fibrous structure that separates the left and right halves of the rectus abdominis muscle along the midline of the abdomen.
What are tendinous intersections?
Tendinous intersections are bands of connective tissue that subdivide the rectus abdominis into smaller muscle bellies, causing the muscle to expand between them during contraction.
Which nerves control the rectus abdominis?
The muscle is innervated by the thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves.
How does the blood supply differ between the upper and lower parts of the muscle?
The upper portion is primarily supplied by the superior epigastric artery (a branch of the internal thoracic artery), while the lower portion is served by the inferior epigastric artery and vein.
What is the sternalis muscle?
The sternalis muscle is an anatomical variation that may be a variant form of either the rectus abdominis or the pectoralis major.