Unit 3: Muscular System

Orbicularis Oris

Action: closes lips

Orbicularis Oculi

Action: closes eyes

Buccinator

Action: compresses cheek

Platysma

Action: tenses skin of neck, pulls lower lip back and down

Temporalis

Insertion: coronoid process of mandible
Action: elevates and retracts mandible

Masseter

Action: elevate mandible

Sternocleidomastoid

Origin: manubrium and sternal end of clavicle
Insertion: mastoid process
Action: unilateral - laterally flexes head to same side and rotates head to opposite side; bilateral - flexes head

Splenius capitis

Action: unilateral - laterally flexes and rotates head to same side; bilateral - extends head

Semispinalis capitis

Action: unilateral - rotates vertebral column and head to opposite side; bitateral - extends vertebral column and head

Spinalis group

Action: extends vertebral column

Longissimus group

Action: unilateral - laterally flexes vertebral column to same side and rotates head to same side; bilateral - extends vertebral column and head

Iliocostalis group

Action: unilateral - laterally flexes vertebral column to same side; bilateral - extends vertebral column

Diaphragm

Action: prime mover of inspiration

External intercostals

Action: pulls ribs toward one another to elevate rib cage; aids in inspiration

Internal intercostals

Action: draws ribs together to depress rib cage; aid in forced expiration

Rectus Abdominis

Origin: pubic crest and symphysis
Insertion: xiphoid process; costal cartilages of ribs 5-7
Action: flexes and rotates vertebral column; compresses abdominal wall

External Oblique

Action: unilateral - rotates and laterally flexes vertebral column to same side; bilateral - flexes vertebral column and compresses abdominal wall

Internal Oblique

Action: same as external oblique

Transversus Abdominis

Action: compresses abdominal wall

Levator scapulae

Action: elevates, adducts (retracts) and inferiorly rotates scapula; laterally flexes neck to same side when scapula is fixed

Rhomboid major

Action: elevates, adducts (retracts), inferiorly rotates and stabilizes scapula

Rhomboid minor

Action: same as rhomboid major

Serratus anterior

Action: stabilizes, superiorly rotates and protects scapula (prime mover of scapula protraction)

Trapezius

Origin: occipital bone; ligamentum niche; spinous process of C7-T12
Insertion: clavicle; acromion process and spine of scapula
Action: superior fibers - elevate and superiorly rotate scapula; middle fibers - retract (adduct) scapula; inferior fibers - depress and superiorly rotate scapula

Pectoralis minor

Origin: ribs 3-5
Insertion: coracoid process of scapula
Action: protracts and depresses scapula

Deltoid

Origin: acromial end of clavicle; acromion and spine of scapula
Insertion: deltoid tuberosity of humerus
Action: anterior fibers – flex and medially rotate arm; middle fibers – prime mover of arm abduction; posterior fibers – extend and laterally rotate arm

Coracobrachialis

Origin: coracoid process of scapula
Insertion: middle medial shaft of humerus
Action: adducts and flexes arm

Pectoralis major

Insertion: greater tubercle of humerus
Action: adducts, medially rotates and flexes arm (prime mover of arm flexion)

Latissimus dorsi

Insertion: intertubercular sulcus of humerus
Action: adducts, medially rotates and extends arm (prime mover of arm extension)

Teres major

Action: adducts, medially rotates, and extends arm

Supraspinatus

Origin: supraspinous fossa of scapula
Insertion: greater tubercle of humerus
Action: abducts arm

Infraspinatus

Origin: infraspinous fossa of scapula
Insertion: greater tubercle of humerus
Action: laterally rotates arm

Teres minor

Origin: upper dorsal lateral border of scapula
Insertion: greater tubercle of humerus
Action: laterally rotates arm

Subscapularis

Origin: subscapular fossa of scapula
Insertion: lesser tubercle of humerus
Action: medially rotates arm

Rotator cuff muscles = spraspinatus, infraspinatus, teres minor, subscapularis (SITS)

Function: stabilize the shoulder joint

Biceps brachii

Origin: long head - supraglenoid tubercle of scapula; short head - coracoid process of scapula
Insertion: radial tuberosity
Action: flexes and supinates forearm; long head also flexes arm

Brachialis

Origin: anterior humerus
Insertion: coronoid process of ulna
Action: flexes forearm

Brachioradialis

Action: flexes forearm

Triceps brachii

Origin: long head - infraglenoid tubercle; lateral head - posterior humerus above radial groove; medial head - posterior humerus below radial groove
Insertion: olecranon of ulna
Action: primary extensor of forearm; long head also extends and adducts arm

Flexor carpi ulnaris

Origin: medial epicondyle of humerus
Action: flexes and adducts hand

Palmaris longus

Origin: medial epicondyle of humerus
Action: weak hand flexor

Flexor carpi radialis

Origin: medial epicondyle of humerus
Action: flexes and abducts hand

Pronator teres

Origin: medial epicondyle of humerus
Insertion: lateral surface of radius
Action: pronates forearm

Flexor digitorum superificials

Origin: medial epicondyle of humerus; coronoid process of ulna
Insertion: middle phalanges of fingers 2-5
Action: flexes hand, 2nd - 5th MP joints and PIP joints

Flexor digitorum profundus

Origin: anteromedial surface of ulna; interosseous membrane
Insertion: distal phalanges of digits 2-5
Action: flexes hand, 2nd - 5th MP joints; PIP joints, and DIP joints

Pronator quadratus

Action: prime mover of forearm pronation

Flexor retinaculum

deep fascia that holds tendons against the bone during contraction

Extensor carpi radialis longus

Origin: lateral supracondylar ridge of humerus
Action: extends and abducts hand

Extensor carpi radialis brevis

Origin: lateral epicondyle of humerus
Action: extends and abducts hand

Extensor digitorum

Origin: lateral epicondyle of humerus
Action: extends hands and 2nd - 5th MP joints, PIP joints and DIP joints

Extensor carpi ulnais

Origin: lateral epicondyle of humerus
Action: extends and adducts hand

Extensor retinaculum

deep fascia that holds extensor tendons close to the wrist joint to prevent them from “bowing” during wrist extension

Abductor pollicis

Action: extends and abducts thumb

Extensor pollicis brevis

Action: extends thumb

Extensor pollicis longus

Action: extends thumb