THE MUSCULAR SYSTEM

CH. 6HUMAN ANATOMY 1

I. The Muscular SystemA. General characteristics

1. 600+ skeletal muscles2. about 40% of body mass3. help provide shape of body4. main job = voluntarily controlled movement5. can only pull on point of attachment

a. usually work in pairs/teams for full range of motion6. other muscle types = smooth & cardiac

2

B. Skeletal muscle physiology1. Movement

a. locomotion, response, manipulation w/arms & hands

1) functional qualities allow thisa) irritability (responsiveness)b) contractility (ability to shorten)c) extensibility (ability to stretch)d) elasticity (ability to recoil &

reshape) 3

2. Posture and body position3. Stabilize joints4. Produce heat

a. byproduct of movement & using ATP

5. Protectiona. of internal organs below/around

them

4

C. Gross Anatomy1. made of muscle fibers

a. elongated cells w/ myofilaments 1) proteins that contract to move

2) create striationsb. each is covered by endomysium

2. several fibers are bound into fascicles

a. held together by the perimysium5 6

3. Many fascicles join to form a musclea. entire muscle covered by coarse

epimysium1) may blend into tendons

a) cord that binds muscles directly to bones

b) durable & fit in small spaces2) may blend into aponeuroses

a) sheets that attaches muscles indirectly to bones, cartilage or

connective tissues7 8

9

b. all membranes join together in anchoring muscles 1) entire muscle & tendon are

surrounded by fascia

10

D. Microscopic Anatomy1. skeletal muscles are multinucleate

a. several oval nuclei next to inner sarcolemma (“muscle husk”)

1) muscle cell plasma membrane2. myofibrils fill majority of cytoplasm

a. chains of contractile sarcomeresb. may be thick or thin

1) thick contain protein myosin2) thin contain protein actin3) create alternating light & dark

bands 11 12

13

E. Arrangement1. basic fiber patterns

a. parallel to long axis1) ex: rectus abdominis

b. convergent to a narrow attachment1) ex: pectoralis major

c. unipennate = one-sided diagonal1) ex: extensor digitorum longus

d. bipennate = double-sided diagonal1) ex: rectus femoris

e. multipennate = several diagonal sections combined1) ex: deltoid

f. sphincter = curved1) ex: orbicularis oculi

g. fusiform = tapered ends, thick middle1) ex: biceps brachii

14

15 16

F. Attachment1. 2 points of attachment

a. origin = point of attachment that remains fixed when moving

b. insertion = point that moves when

the muscle contracts1) insertion bone moves toward

origin bone c. may have multiple origins or

insertions 17 18

G. Muscle actions1. act in pairs or groups usually

a. 1 or more muscles move while other(s) relax

b. may play different roles in different actions2. special terms for movers

a. prime mover (a.k.a. agonist): directly performs action

1) ex: biceps brachii when arm is flexing

19

b. Antagonist : oppose motion of the prime movers

1) relax when p.m. contracts2) ex: triceps brachii when arm is

extendingc. Synergist : contract along w/ prime mover

1) aid p.m., makes it more stable2) ex: deltoid & upper pectoralis

major during flexion20

d. Fixator : specialized synergists1) stabilize bones, aid posture &

balance2) ex: erector spinae

muscles around vertebrae

21 11/18/2016 22

H. How muscles are named1. Location – named by associated bone

a. ex: frontalis, brachioradialis, rectus femoris

2. Function – muscle’s actiona. extensor = straightens

1) ex: extensor digitorum longusb. flexor = bends

1) ex: flexor carpi radialis23

c. abductor = takes away1) ex: abductor digiti minimi

d. adductor = brings back1) ex: adductor longus

e. levator = raises, lifts1) ex: levator scapulae

f. masseter = chews

24

3. Shape a. ex: deltoid (triangular),

trapezius (trapezoidal)4. Direction of fibers – in relation to

body’s midline or long axis of limba. rectus = straight

1) ex: rectus abdominisb. oblique = diagonal

1) ex: external obliquec. transversus = across

1) ex: transversus abdominisd. orbicularis = circular

1) ex: orbicularis oculi 25

5. Number of origins a. a.k.a. heads or divisions

1) “-ceps” = heads2) ex: quadriceps, biceps, triceps

6. Points of attachment – both origin & insertion of musclea. ex: sternocleidomastoid,

brachioradialis

26

7. Relative size of muscle – in comparison to nearby muscles

a. vastus – huge 1) ex: vastus lateralis

b. maximus – large 1) ex: gluteus maximus

c. longus – long 1) ex: palmaris longus

d. minimus – small 1)abductor digiti minimi

e. brevis – short 1) ex: peroneus brevis

f. medius – medium 1) ex: gluteus medius 27 28

II. Movement of synovial jointsA. Contraction of skeletal muscles

1. must be stimulated by nerve impulsesa. motor unit = 1 neuron + all the muscle

cells it stimulates 2. muscle cells contract “all or none,” not

partiallya. whole muscles react w/ graded

responses (degrees of shortening)

1) due to # of cells stimulated or frequency of stimuli 29

b. Tetanic contraction is normal1) smooth & sustained contractions

a) strong and forceful2) a.k.a. fused / complete tetanus

c. forcefulness increases with # of active motor units working

1) light contraction when only a few muscle cells are stimulated

30

3. Strenuous use causes muscle fatigue a. muscle can no longer contract

1) suspected reasons incl. Ca2+ & K+ ion imbalance, neuromuscular junction problems & oxygen deficit

2) lactic acid accumulates, causing burning sensation

31

4. Types of muscle contractionsa. Isotonic contractions

1) myofilaments slide, muscles shorten & movement occurs

2) ex: most familiar movementsb. Isometric contractions

1) muscles don’t shorten when working against a less movable object

a) creates tension in the muscles2) ex: pushing against a wall

5. Muscle tonea. state of continuous partial contractions by

alternating groups of fibers b. creates firm, healthy muscles ready for action

32

B. Movement categories1. angular, circular, gliding or special

a. depends on shapes of articulating surfaces and positions of ligaments, tendons & muscles

33

2. Angular movements – change angle between bones

a. Flexion = decreases angle1) ex: bending elbow

b. Extension = increases angle1) ex: straighten knee2) Hyperextension = extending

beyond the normal position

34

c. Plantar flexion = foot stretches down & back, pointing toes

d. Dorsiflexion = foot tilts upward toward shin

35

e. Abduction = moves a part away from the median plan

f. Adduction = moves a part toward the medial plane

36

3. Circular movements – rotate a structure around an axis

a. Rotation = bone pivots on its own axis1) ex: shaking head “no”

b. Circumduction = distal end of body part moves in a circle

37

c. Supination = turning hand palm side up so radius & ulna are parallel

d. Pronation = turning hand palm side down so radius & ulna are crossed

38

4. Gliding movements – one articular surface moves over surface of the other

a. occurs in carpals and tarsals

39

5. Special movements – unique, unusual or limited

a. Inversion = turns sole of foot inward 1) similar to supinationb. Eversion = turns sole of foot outward

1) similar to pronation

40

c. Protraction = moves body part forwardd. Retraction = moves body part backward

41

e. Elevation = moves a body part upf. Depression = moves a body part down

42

g. Opposition = movement of thumb across palm in relation to other digits

43