Abdominal muscles

Question 1

Abdominal muscles

Answer 1

• Located between the lower border of the thorax, lumbar backbone and the superior border of the pelvis
• Developed from ventral myotoms
• Innervated by the ventral rami of the spinal nerves
• Organised into three groups:

1. Ventral: rectus abdominis m. and pyramidalis m.
2. Lateral: External oblique abdominal m., internal oblique abdominal m., transverse abdominal m. and the cremaster m.
3. Dorsal: Quadratum lumborum m.

Question 2

Rectus abdominis muscle

Answer 2

• long, flat
• Origin: xiphoid process and ventral side of cartilaginous parts of 5th, 6th and 7th ribs
• Insertion: Pubic tubercule, next to the pubic symphysis
• Divided transversely by 3-4 tendons - intersectional tendons
• They grow together with the ventral layer of the rectus sheath
• Innervation: Abdominal branches of the intercostal nerves Th5 - L2 (L1)
• Function: trunk anteflexion, at fixed backbone elevates pelvis and forms part of the abdominal press

Question 3

Pyramidalis muscle

Answer 3

• Small triangular muscle
• Located in front of the rectus abdominis muscle
• Origin: Pubic tubercule
• Ascends cranially and medially
• Insertion: lower part of linea alba
• Innervation: Abdominal branches of the intercostal nerves
• Function: firms up the muscle sheath of the rectus abdominis muscle

Question 4

External oblique abdominal muscle

Answer 4

• Wide flat muscle
• Origin: external plane of 5th to 12th rib
• Fibres run anteriory and mediocaudally (corresponds to external intercostal mm.) and it passes into a wide aponeurosis
• This aponeurosis represents the anterior layer of the rectus sheath
• Insertion: linea alga, inguinal ligament and the external lib of the crista iliaca
• Innervation: Intercostal nerves Th5-12 (abdominal branches)
• Function: UC - contralateral rotation of the trunk and backbone lateroflexion to the homolateral side, BC - anterflexion of the trunk and significantly contributes to the abdominal press

Question 5

Internal oblique abdominal muscle

Answer 5

• Wide, flat muscle, under the external oblique m.
• Origin: lateral part of the inguinal ligament, ASIS, crista iliaca (linea intermedia) and lamina profunda fasciae thoraculumbalis
• Runs mediocranially (corresponging to internal intercostal mm.) and passes into a wide aponeurosis
• Insertion: inferior margin of 9th to 12th rib
• Contributes to forming both layers of the recus sheath
• Innervation: Abdominal branches of the intercostal nerves Th5-Th12, iliohypogastric n. and genitofemoral n.
• Function: UC - trunk rotation to HLS and backbone lateroflexion to HLS, BC - anteflexion of the backbone, participates in expitation and in the abdominal press

Question 6

Transverse abdominal muscle

Answer 6

• Wide flat muscle
• Origin: internal surface of six caudal ribs, lamina profunda fasciae thoracolumbalis, crista iliaca (internal lip), ASIS and on the inguinal ligament
• Fibres run anteriorly and medially, in an almost transverse plane and pass into the dorsal layer of the rectus sheath
• Insertion: linea alba
• Innervation: Abdominal branches of the intercostal nerves Th5-Th12
• Function: UC - backbone lateroflexion to HLS, BC - belly flattening, and contributes to abdominal press and respiration

Question 7

Cremaster muscle

Answer 7

• Muscle fibres that derivate from the internal oblique abdominal m. and the transverse abdominal m. that enters the spermatic cord through the inguinal canal
• The fibres create loop around the testes
• In women it is very reduced and some rudimentary fibres attach themselves to the ligamentum teres uteri
• Innervation: genital branch of the genitofemoral nerve
• Function: In men - elevates testis and forms an integral part of the spermatic cord, in women its function is entirely insignificant

Question 8

Quadratum lumborum muscle

Answer 8

• Forms a muscular background of the dorsal abdominal wall between the 12th rib and the iliac bone
• Origin: internal lip of crista iliaca and the iliolumbar ligament
• Insertion: Costal processes of L1-L4 and the 12th rib
• Innervation: subcostal nerve from the lumbar plexus
• Function: UC - backbone lateroflexion to HLS and at BC - dosiflexion (extension) of the backbone