Muscle Origin, Insertion, Action

Rectus Abdominis

• Originates from the pubic crest and pubic symphysis.
• Inserts at the xiphoid process and the costal cartilages of the 5th, 6th, and 7th ribs.
• Functions to flex and rotate the vertebral column.

External Oblique

• Originates from the outer surfaces of the lower 8 ribs.
• Inserts into the linea alba via aponeurosis, pubic crest, tubercle, and iliac crest.
• Acts to flex the vertebral column, compress the abdominal wall, and rotate the trunk laterally.

Internal Oblique

• Originates from the lumbar fascia, iliac crest, and inguinal ligament.
• Inserts into the linea alba, pubic crest, last 3-4 ribs, and costal margin.
• Functions to flex the vertebral column, compress the abdominal wall, and rotate the trunk.

Transverse Abdominis

• Originates from the cartilage of the last 6 ribs, lumbar fascia, iliac crest, and inguinal ligament.
• Inserts at the linea alba and pubic crest.
• Works to compress abdominal contents.

Platsyma

• Originates from the skin over the lower neck, upper lateral chest, and pectoral muscles.
• Inserts at the lower margin of the mandible.
• Functions to tense the neck and depress the mandible.

Sternohyoid

• Originates from the sternum (manubrium) and clavicle.
• Inserts at the lower margin of the hyoid bone.
• Acts to depress the hyoid bone and larynx.

Sternocleidomastoid

• Originates from the sternum (manubrium) and medial point of the clavicle.
• Inserts at the mastoid process of the temporal bone and superior nuchal line of the occipital bone.
• Functions to flex and laterally rotate the cervical spine, move the head, and extend the neck.

Rhomboids

• Originates from the spinous processes of C7-T1 (minor) and T2-T5 (major).
• Inserts at the medial border of the scapula.
• Stabilizes the scapula.

Trapezius

• Originates from the occipital bone, ligamentum nuchae, and spinous processes of C7-T12.
• Inserts continuously along the acromion, spine of scapula, and clavicle.
• Functions to stabilize, rotate, retract, and raise the scapula.

Latissimus Dorsi

• Originates from T6-L5 vertebrae, lower 3-4 ribs, iliac crest, and scapula.
• Inserts into the intertubercular groove of the humerus.
• Performs arm extension, adduction, and medial rotation.

Iliocostalis

• Originates from the iliac crest, inferior 6 ribs, and ribs 3-6.
• Inserts at the angles of the ribs and transverse processes of C4-C6.
• Functions to extend and laterally flex the spine.

Longissimus

• Originates from the transverse processes of lumbar through cervical vertebrae.
• Inserts at the transverse processes of cervical and thoracic vertebrae and the mastoid process.
• Acts to extend and laterally flex the spine, and to extend the head while turning the face towards the same side.

Quadratus Lumborum

• Originates from the iliac crest and lumbar fascia.
• Inserts at the 12th rib and transverse processes of L1-L4.
• Functions to flex the vertebral column laterally, maintain upright posture, and assist in forced inspiration.

Intercostals

• Originates from the superior surface of the rib above.
• Inserts into the rib below.
• Functions to draw the ribs together and depress the rib cage during expiration.