Abdominal Muscles

The abdominal muscles can be divided into 4 regions:

• Anterolateral Region
• posterior region
• Upper Region
• Lower Region

Anterolateral Region

1. ANTERIOR ABDOMINAL RECTUM

Superior Insertion : External and inferior surface of 5th to 7th costal cartilages and xiphoid process

Inferior Insertion : Body of pubis and pubic symphysis

Innervation : Last 5 intercostal nerves

Action : Increased intra-abdominal pressure (Expiration, Vomiting, Defecation, Urination and Childbirth)

* Fixed in the Chest : Retroversion of the pelvis

* Fixed in the Pelvis : Flexion of the trunk (+ or – 30°)

2. ABDOMINAL PYRAMID

Upper Insert : Alba Line

Inferior Insertion : Body of pubis and anterior pubic ligament

Innervation : 12th intercostal nerve

Action : Tense the linea alba

3. EXTERNAL ABDOMINAL OBLIQUE

Superior Insertion : External surface of last 7 ribs

Inferior Insertion : Anterior ½ of the iliac crest, ASIS, pubic tubercle and linea alba

Innervation : last 4 intercostal nerves, iliohypogastric and ilioinguinal nerves

Action :

* Unilateral Contraction : Rotation with chest rotating to the opposite side

* Bilateral contraction : Flexion of the trunk and increase in intra-abdominal pressure

4. INTERNAL ABDOMEN OBLIQUE

Superior Insertion : Last 3 costal cartilages, pubic crest and linea alba

Inferior Insertion : Iliac crest, ASIS, and inguinal ligament

Innervation : last 4 intercostal nerves, iliohypogastric and ilioinguinal nerves

Action : Same as the External Oblique, but rotates the thorax to the same side.

5. TRANSVERSE ABDOMEN

Posterior Insertion : Inner surface of last 6 costal cartilages, thoracolumbar fascia, iliac crest, and inguinal ligament

Anterior Insertion : Linea alba and pubic crest

Innervation : 5 last intercostals, iliohypogastric and ilioinguinal nerves

Action : Increase intra-abdominal pressure and stabilization of the lumbar spine

posterior region

1. LUMBAR SQUARE

Superior Insertion : 12th rib and transverse process of 1st to 4th lumbar vertebrae

Inferior Insertion : Iliac crest and ileolumbar ligament

Innervation : 12th intercostal nerve and L1

Action : Homolateral trunk tilt and 12th rib depression

2. ILIOPSOAS

Iliac

Superior Insertion : Superior 2/3 of the iliac fossa, iliac crest and sacral wing

Lower Insertion : Lesser Trochanter

Innervation : Femoral Nerve (L2 – L3)

Action : Hip flexion, pelvis anteversion and lumbar spine flexion (30° – 90°)

psoas major

Superior Insertion : Transverse process of lumbar vertebrae, intervertebral bodies and discs of the last thoracic and all lumbar

Lower Insertion : Lesser Trochanter

Innervation : Superior and inferior nerve of the psoas major muscle (L1 – L3)

Action : Thigh flexion, lumbar spine flexion (30° – 90°) and homolateral bending

3. PSOAS MINOR (It is usually absent)

Superior Insertion : Vertebral body of T12 and L1

Lower Insertion : Iliopectineal Eminence

Innervation : L1

Action : Flexion of the pelvis and lumbar spine

Upper Region

1. DIAPHRAGM

Origin : Inner surface of the last 6 ribs, inner surface of the xiphoid process and vertebral bodies of the upper lumbar vertebrae

Insertion : In the central tendon (aponeurosis)

Innervation : Phrenic nerve (C3 – C5) and last 6 intercostal nerves (proprioception)

Action : Inspiratory, as it reduces the internal pressure of the rib cage allowing air to enter the lungs, stabilization of the spine and expulsions (defecation, vomiting, urination and delivery)

Lower Region

1. ANAL LIFTER

The levator ani usually shows a two-part separation:
– Pubococcygeus
– Iliococcygeus

Origin : Between the superior ramus of the pubis and the ischial spine

Insertion : Coccyx, sphincter of anus and at the central tendon point of the perineum
Innervation : Pudendal Plexus (S3 - S5)

Action : Supports and slightly elevates the pelvic floor, resisting increased intra-abdominal pressure, such as during forced expiration

2. ISCHIOCOCCYGEOUS

Origin : Apex of ischial spine and sacrospinous ligament

Insertion : Margin of the coccyx and on the lateral surface of the sacrum

Innervation : Pudendal Plexus (S4 - S5)

Action : Pulls the coccyx ventrally, supporting the pelvic floor against intra-abdominal pressure

ABDOMINAL MUSCLES Previous View - Surface Layer

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000 .

ABDOMINAL MUSCLES Previous View - Middle Layer

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

ABDOMINAL MUSCLES Previous View - Deep Layer

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

ABDOMINAL MUSCLES iliopsoas

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

ABDOMINAL MUSCLES Iliopsoas action

Source: NETTER, Frank H.. Atlas of Human Anatomy. 2nd edition Porto Alegre: Artmed, 2000.

ABDOMINAL MUSCLES Internal View of the Posterior Abdominal Wall

Source: NETTER, Frank H.. Atlas of Human Anatomy . 2nd edition Porto Alegre: Artmed, 2000.