Makindo Medical Notes

Anatomy

Muscles of the Abdominal Region - Listed Alphabetically

Cremaster

Origin: Inguinal ligament
Insertion: Forms thin network of muscle fascicles around the spermatic cord and testis (or around the distal portion of the round ligament of the uterus)
Action: Elevates testis (not well developed in females)
Innervation: Genital branch of the genitofemoral nerve
Artery: Cremasteric a., a branch of the inferior epigastric a.
Notes: The cremaster m. is the internal abdominal oblique muscle's contribution to the coverings of the spermatic cord and testis; the cremasteric reflex may be elicited by stroking the medial thigh (femoral branch of the genitofemoral n.) (Greek, cremaster = suspender)

Dartos

Origin: Subcutaneous connective tissue of the scrotum and the penis (or labium majus and clitoris)
Insertion: Skin of the scrotum and penis (or labium majus and clitoris)
Action: Elevates testis (tenses skin in the female pudendal region)
Innervation: Postganglionic sympathetic nerve fibers arriving via the ilioinguinal and posterior scrotal nerves
Artery: Cremasteric a., posterior scrotal (labial) a.
Notes: Dartos elevates the testis in response to cold (it is modified arrector pili fibers) (Latin, dartos = leather)

External Abdominal Oblique

Origin: Lower 8 ribs
Insertion: Linea alba, pubic crest & tubercle, anterior superior iliac spine & anterior half of iliac crest
Action: Flexes and laterally bends the trunk
Innervation: Intercostal nerves 7-11, subcostal, iliohypogastric, and ilioinguinal nerves
Artery: Musculophrenic a., superior epigastric a., intercostal aa. 7-11, subcostal a., lumbar aa., superficial circumflex iliac a., deep circumflex iliac a., superficial epigastric a., inferior epigastric a., superficial external pudendal a.
Notes: The inguinal ligament is a specialization of the external oblique aponeurosis; external spermatic fascia is its contribution to testis and spermatic cord coverings.

Interfoveolar

Origin: Transversus abdominis fibers superficial to the inferior epigastric vessels
Insertion: Anterior lamina of femoral sheath, immediately distal to origin of inferior epigastric vessels
Action: Compresses abdominal contents
Innervation: Iliohypogastric and ilioinguinal nerves
Artery: Inferior epigastric a.
Notes: An inconstant part of the transversus abdominis, sometimes replaced by a ligament (interfoveolar ligament)

Internal Abdominal Oblique

Origin: Thoracolumbar fascia, anterior 2/3 of iliac crest, lateral 2/3 of inguinal ligament
Insertion: Lower 3 or 4 ribs, linea alba, pubic crest
Action: Flexes and laterally bends the trunk
Innervation: Intercostal nerves 7-11, subcostal, iliohypogastric, and ilioinguinal nerves
Artery: Musculophrenic a., superior epigastric a., intercostal aa. 7-11, subcostal a., lumbar aa., superficial circumflex iliac a., deep circumflex iliac a., superficial epigastric a., inferior epigastric a., superficial external pudendal a.
Notes: Anterior fibers of internal oblique course up and medially, perpendicular to the fibers of external oblique; the cremaster muscle and fascia is the internal oblique’s contribution to the testis coverings.

Psoas Major

Origin: Bodies and transverse processes of lumbar vertebrae
Insertion: Lesser trochanter of femur (with iliacus) via iliopsoas tendon
Action: Flexes the thigh; flexes & laterally bends the lumbar vertebral column
Innervation: Branches of the ventral primary rami of spinal nerves L2-L4
Artery: Subcostal a., lumbar aa.
Notes: The genitofemoral nerve pierces the anterior surface of the psoas major m. (Greek, psoas = the muscles of the loins)

Pyramidalis

Origin: Pubis, anterior to the rectus abdominis
Insertion: Linea alba
Action: Draws the linea alba inferiorly
Innervation: Subcostal nerve
Artery: Subcostal a., inferior epigastric a.
Notes: The pyramidalis m. is not always present.