Muscles of the Body

Muscles of Facial Expression

• Buccinators
    - Action: Compresses cheek (as in sucking)
    - Origin: Molar alveolar region of mandible and maxilla
    - Insertion: Muscles and skin of lips

• Orbicularis Oris
    - Action: Squeezes closed and protrudes lips (as in kissing)
    - Origin: Maxilla and mandible around mouth
    - Insertion: Muscles and skin of lips

• Zygomaticus Major
    - Action: Draws angle of mouth up (as in smile)
    - Origin: Zygomatic bone
    - Insertion: Skin and muscle at corners of mouth

• Frontalis
    - Action: Raises eyebrow, wrinkles forehead
    - Origin: Galea aponeurotica (scalp tendon)
    - Insertion: Skin of eyebrows

• Orbicularis Oculi
    - Action: Squeezes eye closed (as in squinting)
    - Origin: Frontal bone on medial wall of orbit
    - Insertion: Eyelids

Muscles that Act on the Jaw (Mastication and Facial Expression)

• Masseter
    - Action: Elevates mandible (closing mouth)
    - Origin: Zygomatic arch and bone
    - Insertion: Mandible ramus and angle

• Temporalis
    - Action: Elevates mandible
    - Origin: Temporal, frontal, parietal bones
    - Insertion: Coronoid process of mandible

• Platysma
    - Action: Pulls lower lip down (as in frowning), lowers jaw (opening mouth)
    - Origin: Fascia of pectoralis
    - Insertion: Mandible, skin of lower face

Muscles that Act on Neck (Move Head)

• Sternocleidomastoid
    - Action: Flexes neck (cocking head to one side, or flex down if both sides)
    - Origin: Manubrium, clavicle (medial third)
    - Insertion: Mastoid process of temporal bone

• Splenius Capitis
    - Action: Extends or hyperextends neck (looking up)
    - Origin: C3-T3 (spinous processes)
    - Insertion: Mastoid process of temporal bone across nuchal line on posterior skull

Muscles that Act on Shoulder (Move Arm)

• Deltoid (anterior)
    - Action: Flexion and medial rotation of humerus at shoulder
    - Origin: Clavicle
    - Insertion: Deltoid tuberosity of humerus

• Deltoid (middle)
    - Action: Abducts humerus at shoulder (upward flap)
    - Origin: Acromion
    - Insertion: Deltoid tuberosity of humerus

• Deltoid (posterior)
    - Action: Extension and lateral rotation of humerus
    - Origin: Scapular spine
    - Insertion: Deltoid tuberosity of humerus

• Pectoralis Major
    - Action: Flexion, adduction, medial rotation of humerus at shoulder (bench press)
    - Origin: Sternum to rib 7, medial half of clavicle
    - Insertion: Intertubercular groove of humerus

• Latissimus Dorsi
    - Action: Extension, adduction, medial rotation of humerus at shoulder (pulls down)
    - Origin: T7-L5, ribs 10-12, iliac crest
    - Insertion: Intertubercular groove of humerus (travels under axillary region)

Rotator Cuff Muscles (Stabilization of Glenoid Fossa)

• Subscapularis
    - Action: Medially rotates humerus at shoulder, stabilizes shoulder
    - Origin: Subscapular fossa of scapula
    - Insertion: Lesser tubercle of humerus

• Supraspinatus
    - Action: Abducts arm at shoulder, stabilizes shoulder
    - Origin: Supraspinous fossa of scapula
    - Insertion: Superior part of greater tubercle of humerus

• Infraspinatus
    - Action: Laterally rotates humerus at shoulder, stabilizes shoulder
    - Origin: Infraspinous fossa of scapula
    - Insertion: Middle part of greater tubercle of humerus

• Teres Minor
    - Action: Adducts and laterally rotates humerus at shoulder, stabilizes shoulder
    - Origin: Lateral border of scapula
    - Insertion: Inferior part of greater tubercle of humerus

Muscles that Act on Scapula (Move Shoulder)

• Levator Scapulae
    - Action: Elevates, adducts (retracts) scapula (bringing shoulder up/in to ear)
    - Origin: Transverse processes C1-C4
    - Insertion: Medial border of scapula, superior to spine

• Rhomboideus Major
    - Action: Adducts (retracts) scapula (pulling shoulders back and up)
    - Origin: T2-T5 spinous processes
    - Insertion: Medial border of scapula

• Serratus Anterior
    - Action: Abducts scapula (raises arm, pulls shoulder forward, as in punching)
    - Origin: Ribs 1-9
    - Insertion: Anterior surface of vertebral border of scapula

• Trapezius (upper)
    - Action: Elevates scapula (as in shrugging)
    - Origin: Occipital bone, C1-C7 spinous processes
    - Insertion: Lateral 1/3 of clavicle and acromion process

• Trapezius (middle)
    - Action: Retracts and elevates scapula (pulling shoulders back and up)
    - Origin: T1-T5 spinous processes
    - Insertion: Spine of scapula

• Trapezius (lower)
    - Action: Retracts and depresses scapula (pulling shoulders back and down)
    - Origin: Spinous process T6-T12
    - Insertion: Medial 1/3 of scapula spine

Muscles that Act on Elbow (Move Forearm)

• Brachialis
    - Action: Flexes elbow (raising forearm)
    - Origin: Anterior distal shaft of humerus
    - Insertion: Coronoid process of ulna

• Pronator Teres
    - Action: Pronates forearm at elbow (twisting forearm toward body)
    - Origin: Medial epicondyle of humerus, coronoid process of ulna
    - Insertion: Lateral midshaft of radius

• Biceps Brachii
    - Action: Flexes elbow, supinates forearm (picking up a jellybean into mouth)
    - Origin: Long: supraglenoid tubercle of scapula; Short: coracoid process of scapula
    - Insertion: Radial tuberosity

• Triceps Brachii
    - Action: Extends forearm at elbow (long head stabilizes shoulder)
    - Origin: Long: infraglenoid tubercle of scapula; Lateral: posterior proximal shaft of humerus; Medial: posterior distal shaft of humerus
    - Insertion: Olecranon of ulna

Muscles that Act on Wrist (Move Hand)

• Extensor Carpi Radialis Brevis
    - Action: Extends wrist, radially deviates wrist (abduction)
    - Origin: Lateral epicondyle of humerus
    - Insertion: Metacarpal III (base)

• Flexor Carpi Radialis
    - Action: Flexes wrist, radially deviates wrist (abduction)
    - Origin: Medial epicondyle of humerus
    - Insertion: Metacarpals II and III (base)

• Extensor Carpi Ulnaris
    - Action: Extends wrist, ulnar deviates wrist (adduction)
    - Origin: Lateral epicondyle of humerus, posterior shaft of ulna
    - Insertion: Metacarpal V (base)

• Flexor Carpi Ulnaris
    - Action: Flexes wrist, ulnar deviates wrist (adduction)
    - Origin: Medial epicondyle of humerus
    - Insertion: Across pisiform and hamate, to metacarpal V (base)

• Extensor Digitorum
    - Action: Extends digits of hand, and wrist
    - Origin: Lateral epicondyle of humerus
    - Insertion: Dorsal side of phalanges 2-5

• Flexor Digitorum
    - Action: Flexes digits of hand, and wrist
    - Origin: Medial epicondyle of humerus
    - Insertion: Anterior side of phalanges 2-5

Muscles of Breathing

• External Intercostals
    - Action: Pulls ribs up toward origin, elevates ribcage to cause inspiration
    - Origin: Inferior border of rib above
    - Insertion: Superior borders of rib below

• Internal Intercostals
    - Action: Pulls ribs down towards origin, depresses rib cage to cause expiration
    - Origin: Superior border of rib below
    - Insertion: Inferior border of rib above

• Diaphragm
    - Action: Drops down to enlarge thoracic cavity, causing inspiration
    - Origin: Xiphoid process, ribs 10-12, costal cartilage 5-9, lumbar vertebrae
    - Insertion: Central tendon (in center of disc-shaped diaphragm)

• External Abdominal Obliques
    - Action: Bilateral action: flexes vertebral column, compresses abdomen; Single action: lateral flexion
    - Origin: Ribs 5-12
    - Insertion: Anterior iliac crest and abdominal aponeurosis (wide tendon)

Muscles that Act at Hip (Move Leg)

• Gluteus Maximus
    - Action: Extends hip (pushing down on a stair), rotates femur laterally
    - Origin: Ilium, sacrum, coccyx
    - Insertion: Gluteal tuberosity of femur

• Adductor Longus
    - Action: Flexes hip, adducts leg
    - Origin: Pubis
    - Insertion: Linea aspera (shorter insertion than adductor magnus)

• Tensor Fasciae Latae
    - Action: Tenses or stabilizes hip and knee joints
    - Origin: Iliac crest near anterior superior spine
    - Insertion: Lateral condyle of tibia

• Adductor Magnus
    - Action: Extends hip and adducts femur
    - Origin: Ischial and pubic rami
    - Insertion: Linea aspera of femur

• Psoas Major
    - Action: Flexes hip (lifting leg to place on stair)
    - Origin: Vertebral bodies T12-L5
    - Insertion: Lesser trochanter of femur

• Gracilis
    - Action: Adducts thigh, flexes knee
    - Origin: Pubis
    - Insertion: Medial aspect of proximal tibia

• Pectineus
    - Action: Adducts, flexes, medially rotates thigh at hip
    - Origin: Pubis and pubic ramus
    - Insertion: From lesser trochanter to superior part of linea aspera of femur

• Sartorius
    - Action: Flexes hip and knee, laterally rotates thigh (cross-legged position)
    - Origin: Anterior superior iliac spine
    - Insertion: Medial aspect of tibial tuberosity

Muscles that Flex Knee (Hamstrings as a Group)

• Biceps Femoris
    - Action: Flexes and laterally rotates knee, extends and adducts hip
    - Origin: Long head: ischial tuberosity; Short head: posterior mid-shaft of femur
    - Insertion: Head of fibula

• Semimembranosus
    - Action: Flexes knee
    - Origin: Ischial tuberosity
    - Insertion: Posterior medial condyle of tibia

• Semitendinosus
    - Action: Flexes knee
    - Origin: Ischial tuberosity
    - Insertion: Medial surface of proximal tibia (slightly anterior to insertion of semimembranosus)

Muscles that Extend Knee (Quadriceps as a Group)

• Rectus Femoris
    - Action: Extends knee, flexes hip
    - Origin: Anterior inferior iliac spine of coxal bone
    - Insertion: Tibial tuberosity and patella

• Vastus Lateralis
    - Action: Extends knee
    - Origin: Greater trochanter, lateral lip of linea aspera (wraps around to anterior surface)
    - Insertion: Tibial tuberosity and patella

• Vastus Medialis
    - Action: Extends knee
    - Origin: Intertrochanteric line, medial lip of linea aspera (wraps around to anterior surface)
    - Insertion: Tibial tuberosity and patella

• Vastus Intermedius
    - Action: Extends knee
    - Origin: Anterior shaft of femur
    - Insertion: Tibial tuberosity and patella

Muscles that Act on Ankle (Move Foot)

• Gastrocnemius
    - Action: Plantar flexion at ankle, flexes knee
    - Origin: Medial and lateral epicondyles of femur
    - Insertion: Calcaneus

• Soleus
    - Action: Plantar flexion at ankle
    - Origin: Proximal third of tibia and fibula
    - Insertion: Calcaneus

• Tibialis Anterior
    - Action: Dorsiflexion and inversion at ankle
    - Origin: Lateral condyle and anterolateral tibia
    - Insertion: Medial cuneiform, under metatarsal 1

Muscles that Act on Vertebral Column

• Spinalis Thoracis
    - Action: Unilaterally: lateral flexion of vertebral column; Bilaterally: extension and hyperextension of vertebral column
    - Origin: T11-12 and L1-2
    - Insertion: ~T4-7

• Rectus Abdominis
    - Action: Compresses abdomen, flexes vertebral column
    - Origin: Pubis crest and symphysis
    - Insertion: Xiphoid process, costal cartilage 5-7