OIA Muscles

Orbicularis oculi

O: Frontal bone and maxilla

I: Skin of eyelids

A: Closes eye (blinking, squinting)

Buccinator

O: Maxilla and mandible

I: Orbicularis oris

A: Compresses cheek (keeps food b/w teeth)

Masseter

O: Zygomatic arch

I: Angle and ramus of mandible

A: Elevates mandible (closes jaw)

External intercostals

O: Inferior border of rib above

I: Superior border of rib below

A: Elevates ribs (inhalation)

Serratus Anterior

O: Ribs 1-8

I: Anterior medial border of scapula

A: Protracts scapula; holds it against thoracic wall

Pectoralis major

O: Medial clavicle, sternum, ribs 1-6

I: Lateral lip of intertubercular sulcus (humerus)

A: Flexes, adducts, medially rotates arm

Subscapularis

O: Subscapular fossa

I: Lesser tubercle of humerus

A: Medially rotates arm; stabilizes shoulder

Deltoid

O: Lateral clavicle, acromion, spine of scapula

I: Deltoid tuberosity

A: Abducts arm (main); also flexes/extends

Levator scapulae

O: Transverse processes C1–C4

I: Superior medial border of scapula

A: Elevates scapula

Splenius Capitis

O: Spinous processes C7–T3

I: Mastoid process

A: Extends & rotates head

Rectus Abdominis

O: Pubic crest & symphysis

I: Ribs 5–7, xiphoid process

A: Flexes vertebral column; compresses abdomen

Triceps Brachii

O: Infraglenoid tubercle + posterior humerus

I: Olecranon process of ulna

A: Extends forearm

Brachialis

O: Distal anterior humerus

I: Coronoid process of ulna

A: Primary forearm flexor

Supinator

O: Lateral epicondyle of humerus and ulna

I: Proximal radius

A: Supinates forearm

Palmaris longus

O: Medial epicondyle of humerus

I: Palmar aponeurosis

A: Flexes wrist; tenses palm

Gluteus Maximus

O: Posterior ilium, sacrum, coccyx

I: Gluteal tuberosity & IT band
A: Extends thigh; laterally rotates; assists abduction

Sartorius

O: Anterior superior iliac spine (ASIS)

I: Medial tibia
A: Flexes, abducts, laterally rotates thigh; flexes leg

Rectus Femoris

O: Anterior inferior iliac spine (AIIS)

I: Patella → tibial tuberosity
A: Extends leg; flexes thigh

Extensor Digitorum Longus

O: Lateral condyle of tibia; fibula
I: Middle & distal phalanges (toes 2–5)
A: Extends toes; dorsiflexes foot

Gastrocnemius muscle

O: Medial & lateral femoral condyles
I: Calcaneus via Achilles tendon
A: Plantarflexes foot; flexes knee

Popliteus

O: Lateral condyle of femur
I: Posterior tibia
A: Flexes knee; medially rotates leg (“unlocks knee”)