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.