GENERAL

Interactions of skeletal muscle

1. Origin – the immovable or less movable muscle attachment

2. Insertion – on the movable bone (or skin)

3. Agonist (prime mover) – most responsible for the movement considered

-a. Biceps brachii – prime mover which flexes the forearm

4. Antagonist – opposes or reverses the movement of the prime mover

-a. Biceps brachii – is an antagonist of the triceps brachii which extend the forearm

5. Synergist – promotes movement of agonist; prevent undesirable movements

-b. Fixators – type of synergist which fix the origin prevent it from moving

Naming skeletal muscle

1. Location – associated body region or bone; temporalis overlies the temporal bone

2. Shape – shape of the muscle; deltoid (triangle) and trapezius (trapezoid)

3. Relative size – maximus, minimus, longus, brevis; gluteus minimus and maximus

4. Directions of fibers – to midline; rectus, parallel; oblique diagonal; transverse

5. Number of origins – biceps, triceps, quadriceps; 2, 3, or 4 heads (origins)

6. Origin and insertion – the origin is named then the insertion; sternocleidomastoid

7. Muscle action – extensor, flexor, adductor, supinator; adductor longus

MUSCLE MECHANICS

Arrangement of fascicles

1. Parallel – fascicles parallel; strap like (sartorius); shorten most but least power

2. Fusiform – also parallel; midsection belly; biceps brachii

3. Pennate – attached obliquely to central tendon; most fibers most powerful

-a. Unipennate – extensor digitorum

-b. Bipennate – rectus femoris)

-c. Multipennate – deltoid

4. Convergent – broad origin, converge large tendon (pectoralis major); fan shape

5. Circular – arranged in concentric ring; often called sphincters; orbicularis oris

Lever systems: Basic principles

1. Lever – a rigid bar which moves on a fixed point; this would be a bone

2. Fulcrum – the fixed point that the lever moves on; joint

3. Effort – is the applied force; in the body this is the result of muscle contraction

4. Load – object providing resistance; body part moved; thing it’s trying to move

Mechanical advantage (power) versus Mechanical disadvantage (speed) levers

1. Mechanical advantage – load is closer to the fulcrum then the effort

-a. Effort – will be less than load

-b. Distance moved – is much less

2. Mechanical disadvantage lever - load is further from fulcrum then effort

-a. Effort – greater than load

-b. Distance moved – is much greater

3. Body – tendencies toward mechanical disadvantage; muscle closer to joint

Types of levers

1. First class levers – in the order: load, fulcrum, effort

-a. Mechanical advantage – load closer to fulcrum than the effort

-b. Mechanical disadvantage – load further from the fulcrum than effort

-c. Body – atlanto-occipito joint neck muscles; flexed forearm

2. Second class levers – in the order: fulcrum, load, effort

-a. Mechanical advantage lever – load is always closer to fulcrum than effort

-b. Body – rare; ball of the foot - body weight (load); calf muscles (effort)

3. Third class levers – in the order: fulcrum, effort, load

-a. Mechanical disadvantage lever – load is always further from fulcrum than effort

-b. Body – mostly; short but powerful contractions; great distance moved; biceps

MAJOR SKELETAL MUSCLES

Head and neck muscles

1. Frontalis – covers forehead and dome of skull

-a. Origin – galea aponeurotica

-b. Insertion – skin of eyebrows

-c. Action – raises eyebrows; wrinkles forehead

2. Occipitalis – overlies posterior occipital

-a. Origin – occipital and temporal bones

-b. Insertion – galea aponeurotica

-c. Action – fixes aponeurosis and pulls scalp posteriorly

3. Orbicularis oculi – thin sphincter muscle of eyelid

-a. Origin – frontal and maxillary bones and ligaments around orbit

-b. Insertion – tissue of eyelid

-c. Action – closes eye

4. Zygomaticus – muscle pair (major and minor); diagonal form cheekbone

-a. Origin – zygomatic bone

-b. Insertion – skin at corner of the mouth

-c. Action – raises lateral corners of mouth upward; smiling

5. Orbicularis oris – mutilayered muscles of the lip

-a. Origin – maxilla and mandible

-b. Insertion – muscles and skin at angles of the mouth

-c. Action – closes, purses, and protrudes lips; kissing and whistling

6. Buccinator – thin cheek muscles; deep to masseter

-a. Origin – maxilla and mandible

-b. Insertion – orbicularis oris

-c. Action – compresses cheek; holds food between teeth when chewing

7. Platysma – unpaired, thin, sheet like

-a. Origin – fascia of chest

-b. Insertion – lower margin of mandible; skin and muscle at corner of mouth

-c. Action – depresses mandible; downward sag of mouth

8. Masseter – powerful muscle; covers lateral mandible

-a. Origin – zygomatic arch and maxilla

-b. Insertion – angle and ramus of mandible

-c. Action – prime mover of jaw closure; elevates mandible

9. Temporalis – fan shaped; covers parts of temporal, frontal and parietal

-a. Origin – temporal bone

-b. Insertion – mandible (corocoid process)

-c. Action – closes jaw; elevates and retracts mandible; side to side movement

10. Digastric – two bellies (origins)

-a. Origin – lower margin mandible; mastoid process of temporal

-b. Insertion – hyoid bone

-a. Action – elevates hyoid during swallowing; depress mandible

11. Sternohyoid – thin medial muscle of neck

-a. Origin – manubrium and medial clavicle

-b. Insertion – hyoid bone

-c. Action – depresses hyoid

12. Sternocleidomastoid – Two headed muscle; fleshy parts on either side of neck

-a. Origin – manubrium; medial clavicle

-b. Insertion – mastoid process of temporal bone; occipital bone

-c. Action – flexion and rotation of head

Thorax muscles

1. Serratus anterior – deep to scapula; inferior to pectoralis muscles

-a. Origin – ribs; serrated

-b. Insertion – scapula (vertebral border)

-c. Action – protracts scapula

2. Trapezius – superficial muscle of posterior thorax

-a. Origin – occipital and vertebrae

-b. Insertion – scapula and clavicle

-c. Action – raises, adducts, rotates scapula

3. Levator scapulae – back and side of neck; deep to trapezius

-a. Origin – cervical vertebrae

-b. Insertion – scapula (medial border)

-c. Action – elevates, adducts scapula

4. Rhomboids – minor and major; deep to trapezius

-a. Origin – cervical and thoracic vertebrae

-b. Insertion – scapula (medial border)

-c. Action – adduct scapula

5. Pectoralis major – large fan shaped muscle; covers upper portion of chest

-a. Origin – sternum, ribs, clavicle

-b. Insertion – humerus (intertubercular groove)

-c. Action – medial rotation; adduction of arm

6. Latissimus dorsi – broad, flat, triangular muscle of lower back

-a. Origin – thoracic and lumbar vertebrae; iliac crest

-b. Insertion – humerus (intertubercular groove)

-c. Action – extend, adduct, medial rotate arm

7. Deltoid – thick muscle forming rounded shoulder mass

-a. Origin – clavicle and scapula

-b. Insertion – humerus (deltoid tuberosity)

-c. Action – abduction of arm

8. Rotator cuff muscles – supraspinatus, infraspinatus, subscapularis, teres minor

9. Supraspinatus – posterior aspect of scapula

-a. Origin – scapula (above spine)

-b. Insertion – humerus (greater tubercule)

-d. Action – stabilizes shoulder joint; abduction of arm

10. Infraspinatus – posterior scapula

-a. Origin – scapula (below spine)

-b. Insertion – humerus (greater tubercule)

-c. Action – stabilizes shoulder joint; lateral rotates arm

11. Subscapularis – part of posterior wall of axilla

-a. Origin – scapula (anterior)

-b. Insertion – humerus (lesser tubercule)

-c. Action – stabilizes shoulder joint; medial rotator of humerus

12. Teres minor – inferior to infraspinatus; rotator cuff muscle

-a. Origin – scapula (posterior surface)

-b. Insertion – humerus (greater tubercule)

-c. Action – stabilize shoulder joint; lateral rotate arm

13. Teres major – inferior to teres minor; part of posterior axilla

-a. Origin – scapula (posterior)

-b. Insertion – humerus (intertubercular groove)

-c. Action – extend, medial rotate, adduct arm

Abdominal muscles

1. Rectus abdominis – medial superficial; ensheathed by aponeurosis

-a. Origin – pubis (crest and symphysis)

-b. Insertion – xiphoid process and ribs (costal cartilage 5 – 7)

-c. Action – compresses abdomen; flex and rotate lumbar region

2. External oblique – most superficial lateral; fibers run down and medially

-a. Origin – ribs (lower 8)

-b. Insertion – linea alba; pubis (crest and tubercule); ilium (crest)

-c. Action – compress abdomen; rotate and flex trunk

3. Internal oblique – fibers upward and medially; except inferior

-a. Origin – lumbar fascia, iliac crest

-b. Insertion – linea alba, pubis, ribs

-c. Action – compresses abdomen; rotate and flex trunk

4. Transverse abdominis – deepest; horizontal fibers

-a. Origin – lumbar fascia, ribs, ilium (crest)

-b. Insertion – linea alba, pubis (crest)

-c. Action – compresses abdomen

Upper extremities

1. Brachialis – distal humerus; deep to biceps brachii

-a. Origin – humerus; distal end

-b. Insertion – ulna (coranoid process)

-c. Action – flex elbow (ulna)

2. Brachioradialis – superficial; lateral forearm

-a. Origin – humerus; distal end

-b. Insertion – radius (styloid process)

-c. Action – flex elbow

3. Biceps brachii – two headed

-a. Origin – scapula (short head, coracoid process; long head, lip of glenoid cavity)

-b. Insertion – radius (radial tuberosity)

-c. Action – elbow flexion; supination of forearm

4. Triceps brachii – only posterior muscle of arm; three heads

-a. Origin – long head, scapula; lateral and medial heads, humerus

-b. Insertion – ulna (olecranon process)

-c. Action – extend elbow

5. Pronator teres – two headed; next to brachioradialis

-a. Origin – humerus (medial epicondyle); ulna (coranoid process)

-b. Insertion – radius (mid shaft)

-c. Action – pronates forearm

6. Flexor carpi radialis – diagonal along forearm

-a. Origin – humerus (medial epicondyle)

-b. Insertion – metacarpals

-c. Action – wrist flexor

7. Flexor carpi ulnaris – diagonal along forearm

-a. Origin – humerus (medial epicondyle); ulna (olecranon process)

-b. Insertion – carpals; metacarpal (5^th)

-c. Action – wrist flexor

8. Palmaris longus – small fleshy muscle; often missing

-a. Origin – humerus (medial epicondyle)

-b. Insertion – palmar aponeurosis; skin and fascia of palm

-c. Action – weak wrist flexor

9. Flexor digitorum superficialis – two headed muscle; intermediate muscle layer

-a. Origin – humerus (medial epicondyle); ulna (coronoid process); radius (shaft)

-b. Insertion – middle phalanges

-c. Action – flexes digits 2 to 5; wrist flexion

10. Flexor digitorum profundus – deep anterior muscle

-a. Origin – ulna (anteromedial surface, coronoid process); interosseous membrane

-b. Insertion – distal phalanges

-c. Action – flexes digits 2 to 5

11. Flexor retinaculum – holds most anterior tendons in place; wrist band

-a. Carpal tunnel – between carpals and flexor retinaculum

-b. Carpal tunnel syndrome – overwork fingers, wrist; inflammation; median nerve

12. Extensor carpi radialis longus – parallels brachioradialis; lateral

-a. Origin – humerus

-b. Insertion – metacarpal (2^nd)

-c. Action – extends wrist; abducts wrist

13. Extensor carpi radialis brevis – shorter than and deep to above

-a. Origin – humerus (lateral epicondyle)

-b. Insertion – metacarpal (3^rd)

-c. Action – extends wrist; abducts wrist

14. Extensor carpi ulnaris – most medial posterior superficial muscle

-a. Origin – humerus (lateral epicondyle); ulna

-b. Insertion – metacarpal (5^th)

-c. Action – extends wrist; adducts wrist

15. Extensor digitorum – medial to extensor carpi radialis brevis

-a. Origin – humerus (lateral epicondyle)

-b. Insertion – distal phalanges 2 to 5

-c. Action – extends fingers; extends wrist

16. Extensor retinaculum – holds posterior tendons in place; wrist band

Lower extremities

1. Sartorius – straplike; superficial; obliquely across anterior thigh

-a. Origin – ilium (iliac spine)

-b. Insertion – medial proximal tibia

-c. Action – flexes, abducts, and laterally rotates thigh; flexes knee

2. Adductor longus – overlies middle of adductor magnus

-a. Origin – pubis

-b. Insertion – femur (linea aspera)

-c. Action – adducts, flexes, and medially rotates thigh

3. Gracilis – strap like superficial muscle of medial thigh

-a. Origin – pubis (body and ramus; ischial ramus)

-b. Insertion – tibia (medial side)

-c. Action – adducts thigh; flexes leg

4. Adductor magnus – triangular; large insertion

-a. Origin – ischium and pubis

-b. Insertion – femur (linea aspera)

-c. Action – adducts, laterally rotates femur; flexes and extends hip

5. Fascia lata – deep fascia of the thigh; ensheathes thigh muscles

-a. Ileotibial tract – thickened portion of fascia lata; from iliac crest to knee

6. Tensor fascia latae – anteriolateral aspect of thigh

-a. Origin – ilium (iliac crest and spine)

-b. Insertion – illeotibial tract

-c. Action – flexes and abducts thigh

7. Quadriceps femoris – rectus femoris, vastus lateralis, v. intermedius, v. medialis

8. Rectus femoris – anterior thigh

-a. Origin – ilium (iliac spine); acetabulum

-b. Insertion – patella, tibial tuberosity via patellar ligament

-c. Action – extends knee and flexes thigh

9. Vastus lateralis – lateral aspect of thigh

-a. Origin – femur (greater trochanter, linea aspera)

-b. Insertion – patella, tibial tuberosity via patellar ligament

-c. Action – extends knee and stabilizes knee

10. Vastus intermedius – obscured by rectus femoris

-a. Origin – femur (proximal shaft)

-b. Insertion – patella, tibial tuberosity via patellar ligament

-c. Action – extends knee

11. Vastus medialis – inferomedial aspect of thigh

-a Origin – femur (linea aspera)

-b. Insertion – patella, tibial tuberosity via patellar ligament

-c. Action – extend knee; stabilize patella

12. Gluteus maximus – largest and most superficial of gluteal muscles

-a. Origin – ilium, sacral, coccyx

-b. Insertion – femur (gluteal tuberosity)

-c. Action – extends thigh; laterally rotates and abducts thigh

13. Hamstrings – biceps femoris, semitendinosus, semimembranosus

14. Biceps femoris – most lateral of the group; two heads

-a. Origin – ischium (ischial tuberosity); femur (linea aspera)

-b. Insertion – tibia (lateral condyle); fibula (head)

-c. Action – flexes knee; extends thigh; lateral rotate leg

15. Semitendinosus – medial to biceps femoris

-a. Origin – ischium (ischial tuberosity)

-b. Insertion – tibia (upper shaft)

-c. Action – flexes knee; extends thigh

16. Semimembranosus – deep to semitendinosus

-a. Origin – ischium (ischial tuberosity)

-b. Insertion – tibia (medial condyle)

-c. Action – flexes knee; extends thigh

17. Tibialis anterior – superficial muscle of anterior leg; lateral to tibia

-a. Origin – tibia (lateral condyle); interosseous membrane

-b. Insertion – medial cuneiform; first metatarsal

-c. Action – dorsiflexion; inversion of foot

18. Gastrocnemius – two bellies; posterior calfs

-a. Origin – medial and lateral condyles of femur

-b. Insertion – calcaneus via calcaneal tendon

-c. Action – plantar flexes foot; flexes knee

19. Soleus – broad and flat; deep to gastrocnemius

-a. Origin – tibia, fibula, interossceous membrane

-b. Insertion – calcaneus via calcaneal tendon

-c. Action – plantar flex foot

20. Extensor digitorum longus – anterolateral surface of leg

-a. Origin – tibia (lateral condyle); fibula; interossceous membrane

-b. Insertion – middle, distal phalanges 2 to 5

-c. Action – extends toes; dorsiflexes foot

21. Fibularis (peroneus) longus – lateral, overlies fibula

-a. Origin – fibula (head and lateral portion)

-b. Insertion – 1^st metatarsal; medial cuneiform

-c. Action – plantar flexion and eversion of foot