Abdominal Muscles: This muscle forms the anterior and lateral abdominal wall. It comprises the-
- External Abdominal Obliques
- Internal Abdominal Obliques
- Rectus Abdominis
- Transversus Abdominis
These four muscles form a firm wall which protects the viscera. Help to maintain the erect posture. Contraction of these muscles helps in expiration and to increase the intra-abdominal pressure such as in sneezing, coughing, micturating, defecating, lifting and childbirth.
The four main abdominal muscle is described is given below:
Transversus Abdominis
The transversus abdominis muscle is the deepest of the abdominal muscles, lying internally to the internal abdominal obliques. Its main roles are to stabilize the trunk and maintain internal abdominal pressure.
- Origin
- The deep surface of the lower six costal cartilages
- Lumbar fascia
- Anterior two-thirds of the iliac crest and
- Lateral third of the inguinal ligament.
- Insertion:
- Xiphoid process
- Linea alba and
- Symphysis pubis.
- Nerve supply:
- Lower six thoracic nerves and
- Iliohypogastric and
- Ilioinguinal nerve
- Action:
- Contraction of this muscle has a corset-like effect, narrowing and flattening the abdomen. Stabilize the lumbar spine and pelvis before movement of the lower and /or upper limbs.
Rectus Abdominis
The rectus abdominis is a long strap muscle that extends the entire length of the anterior abdominal wall. When contracting rectus abdominis muscle has the characteristic bumps or bulges that are commonly called ‘the six pack’. The main function of this muscle is to move the body between the ribcage and the pelvis.
- Origin:
- The anterior aspect of the symphysis pubis and
- Pubic crest
- Insertion:
- 5th, 6th and 7th costal cartilages and
- Xiphoid process
- Nerve supply:
- Lower six thoracic nerves
- Action:
- The rectus abdominis is an important postural muscle, flexion of the lumbar spine.
You Might Also Like
External Oblique Muscles
These are on each side of the rectus abdominis. The external abdominal oblique muscle is the largest and most superficial of the four muscles and lies on the sides and front of the abdomen.
- Origin:
- Lower eight ribs (5th – 12th )
- Insertion:
- Anterior half of the iliac crest
- Xiphoid process
- Linea alba
- Pubic crest
- Pubic tubercle
- Nerve supply:
- Lower six thoracic nerves and
- Iliohypogastric and
- Ilioinguinal nerves
- Action:
- Ipsilateral side flexion and
- Contralateral rotation of the trunk.
Internal Oblique Muscles
The rectus abdominis and are located just inside the hipbones. They operate in the opposite way to the external oblique muscles. For example, twisting the trunk to the left requires the left side internal oblique and the right side external oblique to contract together.
The internal abdominal oblique muscle is also a broad thin muscular sheet. It lies deep to the external oblique muscle.
- Origin:
- Thoracolumbar fascia
- Anterior two-thirds of the iliac crest and
- Lateral two-thirds of the inguinal ligament.
- Insertion:
- Inferior borders of the lower three ribs ( 10th -12th )
- Costal cartilages
- Xiphoid process
- Linea alba and
- Symphysis pubis.
- Nerve supply:
- Lower six thoracic nerves and
- Iliohypogastric and
- Ilioinguinal nerve.
- Action:
- Ipsilateral side flexion and rotation of the trunk.