The muscular system contains three main types of muscle: smooth, cardiac, and skeletal. Skeletal muscle is striated and voluntary, attaching to bones to enable movement. It has a layered connective tissue covering and is composed of fibers containing myofibrils of actin and myosin. Contraction occurs when a motor neuron stimulates calcium release, causing myosin bridges to attach to actin and slide the filaments, shortening the muscle. Major skeletal muscles include those of the face, neck, shoulder, arm, abdomen, thigh, leg, foot and toes which work antagonistically or synergistically to enable movement.

1. Muscular System

2. I. Muscle Types
• A. Smooth
– 1. S: muscle which LACKS STRIATIONS (stripes) and
is located in stomach, intestines, bladder, uterus,
and blood vessels
• Arranged in layers
– 2. It is INVOLUNTARY MUSCLE
• Unconsciously contracts
– 3. F: move food through digestive tract, constrict
blood vessels, contract uterus, empty bladder

3. • B. Cardiac
– 1. S: muscle which IS STRIATED located in the
heart and contains INTERCALATED DISKS
• Def of ID: junctions of cardiac muscle cells which
transmit impulses easily and allow the heart to beat as
one
• Cells look as though they are in figure 8 patterns
– 2. it is INVOLUNTARY muscle
– 3. F: to pump blood into heart chambers and
certain blood vessels

4. • C. Skeletal
– 1. S: muscle found connected to bones which IS
STRIATED
• Contain much connective tissue to attach to bones
– 2. they are VOLUNTARY
• Can consciously control contractions
– 3. F: to move head, neck, trunk, limbs, facial
expressions, and many actions like writing, chewing,
talking etc
• ** throughout this unit we will focus on structure
and function of SKELETAL muscle

5. II. Muscle Structure
• A. Connective Tissue Coverings
– 1. Fascia
• Fibrous tissue covering of individual muscle
– 2. Tendon
• Extension of tissue connecting muscle to bone
• Ex: Tendonitis – swelling of tendon at connection
– 3. Epimysium
• Under fascia
– 4. Perimysium
• Separate muscle into bundles
– 5. Endomysium
• Surrounds individual muscle fiber/cell

6. • B. Skeletal Muscle Fibers
– 1. 1 fiber = 1 cell
– 2. sarcolemma – cell membrane
– 3. sarcoplasm – cytoplasm in cell
– 4. myofibrils – parallel fibers in sarcoplasm
• a. myosin
– T H I C K , DA R K protein filament
• b. actin
– Thin,lightprotein filament
• ** actin and myosin make striations in muscle – light/dark

7. – 5. A-bands
• Dark portion of muscle myofibril
– 6. I-bands
• Light portion of muscle myofibril
– 7. Z-lines
• Place where actin myobifrils meet
– 8. Sarcoplasmic reticulum
• Channels running parellel on outside of fiber
– 9. Transverse Tubules – T Tubules
• Channels running opposite SR between SR on outside of fiber
– ** SR and T Tubules communicate signal to whole muscle
when stimulated

8. • C. Skeletal Muscle Contraction
– 1. Neuromuscular Junction
• Def – connection between nerve fiber and muscle
• ** Each muscle is connected to a nerve called a motor
neuron
– 2. Role of myosin and actin
• Myosin cross bridges connect to actin and pull

9. – 3. Process of Contraction
• a. motor neuron releases ACETYLCHOLINE
– Chemical needed for a muscle contraction
• b. actetylcholine stimulates impulses through the SR
and T Tubules
• c. impulses cause Ca+ to move through the muscle
• d. Myosin cross bridges connect to actin myofibrils
because of presence of Ca+
• e. bridges slide actin along myosin = CONTRACTION
• f. Ca+ leave muscle
• g. Myosin releases bridges = MUSCLE RELAXES

10. • D. O2 Debt, Fatigue, and Heat Production
– 1. O2 Debt
• a. if muscles are exercised strenuously, O2 cannot be
supplied fast enough
• b. Lactic Acid builds up
• c. ATP energy (body’s energy) decreases
• d. CO2 increases
• e.O2 must be replenished before more exercise can be done
– may take hours
– ** the O2 needed to replenish is O2 debt
• f. to replenish O2 you automatically breath deep and fast

11. – 2. Muscle fatigue
• a. def – MF occurs when a muscle loses its ability to
contract
• b. causes:
– Blood supply is cut off (no O2)
– Acetylcholine supply runs out in motor neuron
– Build up in lactic acid
• c. cramping results
– Muscle keeps contracting and can’t relax

12. – 3 . Heat Production
– Muscle contractions release heat
– Keeps body at 98.6

13. • E. Muscle responses
– 1. Threshold Stimulus
• a. def – the minimum stimulus strength needed to cause a
muscle contraction
• ** electric stim on muscles uses this on isolated muscles to
help strengthen them
– 2. ALL or NONE response
• a. there are NO partial contractions in muscle FIBERS
• b.Once stimulus is reached, muscle fiber contracts to full
extent
• C.Not all muscle fibers are stimulated – weaker contraction

14. – 3. Contraction types
• a. twitch – a single contraction that lasts only a fraction
of a second
• b. tetany – a sustained forceful contraction which lacks
relaxation
– Ex: holding a heavy box still out on front of your body
• c. tonus – a small sustained contraction in a muscle
which seems to be at rest
– Due to the muscle being contracted rapidly for varying lengths
of time
– Ex: when walking and leg is back
– Ex: maintaining posture

15. • F. Muscle Interactions
– 1. origin
• Def: immovable place where muscle is attached
– 2. insertion
• Def: moveable place where muscle is attached
• ** insertion always moves towards origin
– Ex: Bicep Brachii
• Origin: coracoid process and scapula
• Insertion: radius

16. – 3. Muscles ALWAYS act in groups
• a. prime mover
– The muscle responsible for the most movement
– Ex: lift arm = deltoid
• b. synergists
– Muscles the contract and ASSIST prime mover
– Helpers
• c. antagonist
– Muscle that acts against the prime mover
– Ex: flex arm
» PM – bicep brachii - contracts
» Ant – tricep - extends

17. – 4. muscle fiber types
• a. fast twitch
– Muscles which contract quickly and tire quickly
– Ex: sprinters
• b. slow twitch
– Muscles which contract slow and are more resistant to fatigue
– Ex: marathon runners, weight lifters

18. III. Major Skeletal Muscles
• A. Muscles of Facial Expression
– 1. frontalis
• Lies over frontal bone
– 2. occipitalis
• Lies over occipital bone
– 3. orbicularis oculi
• Around the eye orbit
– 4. orbicularis oris
• Around mouth orbit

19. – 5. buccinator
• Fish face
– 6. zygomaticus
• Smiling
– 7. platysma

20. • B. Muscles of chewing – mastication
– 1. masseter
• Main muscle of chewing
– 2. temporalis
• Lies over temporal bone

21. • C. Muscles that move the head
– 1. sternocleidomastoid
• Head flexion
– 2. splenis capitis
– 2. semispinalis capitis

22. • D. Muscles of the pectoral girdle
– 1. trapezius
• O:
– Occipital bone
– Spinous process of cervical and thoracic vertebrae
• I:
– Clavicle
– Scapula
• A:
– Move scapula
– Raise arm

23. – 2. Rhomboideus Major
– 3. serratus anterior
– 4. pectoralis minor
• O:
– Sternal ends of upper ribs
• I:
– Coracoid process
• A:
– Pull scapula down
– Pull scapula forward
– Raise ribs

24. • E. Muscles that move the Upper Arm
– 1. Pectoralis Major
• O:
– clavicle
– Sternum
– Costal cartilage
• I:
– Humerous
• A:
– Adduct arm
– Rotate humerus
– Pull arm forward

25. – 2. Teres Major
– 3. Latissimus Dorsi
• O:
– Spinous process of vertebrae
– Iliac crest
– Lower ribs
• I:
– Humerous
• A:
– Adducts arm
– Pulls shoulder down and back

26. – 4. supraspinatus
– 5. deltoid
• O:
– Acromion process
– Scapula spine
– Clavicle
• I:
– Humerous
• A:
– Abducts arm – main muscle to abduct

27. – 6. subscapularis
• On anterior side of scapula
– 7. infraspinatus
– 8. teres minor

28. • F. Muscles that move the forearm
– 1. biceps brachii
• O:
– Coracoid process
– Scapula
• I:
– Radius
• A:
– Flex arm at elbow
– Rotate hand laterally

29. – 2. Brachialis
– 3. brachioradialis
– 4. triceps brachii
• O:
– Lateral and medial surfaces of humerous
• I:
– Proximal ulna
• A:
– Extend arm at elbow

30. – 5. supinator
• In charge of supination
– 6. pronator teres
– 7. pronator quadratus

31. • G. Muscle that move the wrist, hand, and
fingers
– 1. flexor carpi radialis
– 2. flexor carpi ulnaris
– 3. extensor carpi radialis longus
– 4. extensor carpi radialis brevis
– 5. extensor carpi ulnaris
– 6. extensor digitorum

32. • H. Muscles of the abdomen
– 1. LINEA ALBA
• CONNECTIVE TISSUE which abdominal muscles connect
to
– 2. external oblique
• O:
– Outer surface of lower rib
• I:
– Linea alba, iliac crest
• A:
– Compress abdomen

33. – 3. internal oblique
• O:
– Iliac crest
• I:
– Rib cartilage, linea alba, pubis
• A:
– Compress abdomen
– 4. Transverse abdominus

34. – 5. Rectus abdominus
• O:
– Pubis
• I:
– Xyphoid process, costal cartilage
• A:
– Compress abdomen, flex vertebral column

35. • I. Muscles that move the Thigh
– 1. tensor fascia latae
– 2. gluteus maximus
• O:
– Sacrum, coccyx, ilium
• I:
– Posterior femur
• A:
– Extend leg at hip

36. – 3. gluteus medius
• Top of maximus over hip
– 4. adductor longus
– 5. adductor magnus
– 6. gracilis
– 7. fascia: sheet of connective tissue which muscle
may connect to

37. • J. Muscles that move the lower leg
– ** the next 3 muscles make up the HAMSTRING
– 1. biceps femoris
• O:
– Ischium and posterior surface of femur
• I:
– Fibula, tibia
• A:
– Flex/rotate leg, extend thigh

38. – 2. semitendinosous
– 3. semimembranous

39. – 4. sartorius
• Longest muscle in body
• Crosses 2 joints
– 5. quadraceps femoris
• Rectus femoris
• Vastus lateralis
• Vastus medialis
• Vastus intermedius

40. • K. Muscles that move ankle, foot, and toes
– 1. tibialis anterior
• O:
– Lateral surface of tibia
• I:
– Tarsals, 1st metatarsal
• A:
– Dorsal flexion and inversion of foot

41. – 2. extensor digitorum longus
• Extends toes -digits
– 3. gastrochnemius
• O:
– Lateral/medial condyles of femur
• I:
– Posterior surface of calcaneous
• A:
– Plantar flexion of foot and flexion of leg at knee
– 4. soleus
– 5. flexor digitorum longus
– 6. peroneous longus