Muscles of the Thorax

external intercostals - origin

lower border of a rib

external intercostals - insertion

upper border of rib below

external intercostals - action

elevate ribs during inspiration

external intercostals - innervation

intercostal nerves

internal intercostals - origin

inner surface of a rib and costal cartilages

internal intercostals - insertion

upper borders of the adjacent ribs below

internal intercostals - action

draw ribs downward during forced expiration

internal intercostals - innervation

intercostal nerves

transversus thoracis - origin

inner surfaces of the lower third of the body of the sternum and adjacent surfaces of the xiphoid process

transversus thoracis - insertion

internal surfaces of the sternocostal joints associated with the second (or third) through the sixth ribs

transversus thoracis - action

depresses the ribs

transversus thoracis - innervation

intercostal nerves

quadratus lumborum - origin

iliolumbar ligament and crest of the ilium

quadratus lumborum - insertion

rib 12 and tips of the transverse processes of the L1 to L4

quadratus lumborum - action

extension and side flexion of lumbar spine, expiration

quadratus lumborum - innervation

ventral ramus of spinal nerve roots T12-L3

psoas major - origin

transverse processes and lateral bodies of the last thoracic and all lumbar vertebrae including the intevertebral discs

psoas major - insertion

lesser trochanter of femur

psoas major - action

forward flexion and side flexion of lumbar spine

flexion of the hip joint

psoas major - innervation

branches of ventral rami L1-L3

iliacus - origin

superior two thirds of the iliac fossa

inner lip of the iliac crest

iliacus - insertion

lesser trochanter of femur

iliacus - action

flexion of hip joint

iliacus - innervation

femoral nerve

rectus abdominis - origin

pubic crest and anterior pubic ligament

rectus abdominis - insertion

on the front wall of the thorax

along a horizontal line passing laterally from the xiphoid process and cutting in that order, the 7th, 6th, and 5th costal cartilages

rectus abdominis - action

expiration

flexion of the spine

rectus abdominis - innervation

lower six or seven thoracic nerves

external oblique - origin

lateral side of ribs 4-12

external oblique - insertion

iliac crest, linea alba, and contralateral rectus sheaths

external oblique - action

bilaterally: flexion of trunk and posterior tilt of pelvis

unilaterally: lateral flexion and contralateral rotation of trunk

external oblique - innervation

lower 6 thoracic nerves

internal oblique - origin

iliac crest, inguinal ligament, and throacolumbar fascia

internal oblique - insertion

ribs 9-12, linea alba and contralateral rectus sheath

internal oblique - action

bilaterally: flexion of the trunk and posterior tilt of pelvis

unilaterally: lateral flexion and ipsilateral rotation of the trunk

internal oblique - innervation

lower 6 thoracic nerves and first lumbar nerve

transversus abdominus - origin

iliac crest, thoracolumbar fascia, inner surface of the cartilages of ribs 6-12 and the inguinal ligament

transversus abdominus - insertion

linea alba

transversus abdominus - action

bilaterally: stabilization of atachment site for other abdominal muscles

compression of abdominal cavity

transversus abdominus - innervation

lower 6 thoracic nerves

first lumbar nerve