The Muscular

System

Chapter 7

600 +

muscles

1

Muscles

• From Latin mus

• “Little mouse”

• ~ 700 skeletal muscles

– 60 in face

• >40 for frowning

• 20 for smiling

2

Function

• 1) Movement of skeleton

• 2) Maintain posture and

body position

• 3) Support soft tissues

• 4) Guard entrances and

exits

• 5) Maintain body temp

3

Types of Muscle Tissue

• Three types:

– Skeletal

– Smooth

– Cardiac

4

Types of Muscle Tissue

5

Skeletal Muscle Tissue

Review • Attach to skeleton

• Voluntary

• Long cylindrical shape

• Multinucleated

• Nuclei near edge

• Striated

• Can contract rapidly

– Need rest

• Largest of three types

– Up to 24 inches long!

6

Skeletal Muscle Cells • Called muscle fibers

• Mys = muscle

• Sarkos = flesh

• All contract

7

Skeletal Muscle (Organ)

• Skeletal muscle

tissue

• Contains 1000s of

muscle cells

• Nervous tissue

• Blood

• Connective tissue

– 3 layers

8

3 Connective

Tissue Layers

• Bundled together by

connective tissue

– Provides strength and

support

• 1) Endomysium – wraps

around individual muscle

fiber

9

3 Connective Tissue Layers • 2) Perimysium – coarser membrane

– encloses a bundle of muscle fibers (called a

fascicle)

– Collagen and elastic fibers, nerves and blood

vessels

10

3 Connective Tissue Layers • 3) Epimysium – Surrounds entire muscle

– Several fascicles wrapped together

– Separates muscle from surrounding tissues and

organs

– Collagen fibers

• Fascia - Encloses entire muscle and

epimysium

– Separates individual skeletal muscles and holds

muscles in place

11

Tendon

• Bundle of collagen

fibers where muscle

meets bone

• All 3 connective

tissue layers taper

and blend

• Interwoven with

periosteum of bone

• Gives “pulling power”

12

Aponeuroisis

• Broad sheet of collagen

fibers

• Attach skeletal muscles

to other skeletal

muscles, not to bone

coverings

13

Muscle structure

14

Skeletal Fibers (cells) • Sarcolemma – cell membrane

• Sarcoplasm – cytoplasm

• Transverse tubules (T tubules)

– form passageways and help with contractions

– Encircle myofibril

• Sarcoplasmic reticulum (SR) – specialized

SER

15

Sarcoplasmic Reticulum • Surround each

myofibril

– Like a crocheted

sweater around your

arm

• Major role

– Store and release

calcium

• Essential for muscle

contraction

16

Myofibrils

• Responsible for muscle

fiber contraction

• Make up muscle fibers

(cells)

• Made of bundles of

myofilaments

• Each contains ~10,000

sarcomeres

17

Sarcomeres • Smallest functional unit

of muscle cell

• Each can contract

• Arranged end-to-end

• Segment from z line to z

line

18

Myofilaments

• Made of protein

• Two types:

– Actin

– Myosin

19

Actin Filaments

• Thin filaments

• At ends of sarcomere

• Made up of protein actin

• Also contain regulatory proteins troponin

and tropomyosin

20

Actin Filaments

• Form light band

– Parts of two adjacent

sarcomeres

– Contain only thin

filaments

– Actin filaments slide

toward each other in

contraction

21

Myosin Filaments

• Larger, thicker

• In middle of sarcomere

• Made up of protein

myosin

• Ends have projections:

– Myosin heads = Cross

bridges

• Link thick and thin

filaments during

contraction

22

Striations • I bands (light)

– Thin actin attached to Z line (midline boundary)

• A bands (dark)

– Thick myosin overlapping actin

– Contains H zone (central region)

– Contains M line (thickening)

23

Sarcomere Structure

24

http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/chapter10/animation__sarcome

re_contraction.html

Sarcomeres

25

Another Look

26

27

Sliding Filament Model

• Explanation of sarcomere contraction

• Sarcomeres shorten when crossbridges pull on thin filaments at their binding sites

• Must have calcium to start contraction!

28

Sliding Filament Theory

29

– 1) Myosin crossbridge attaches to actin binding site

– 2) Actin filament is pulled closer

– 3) Filament is let go

– 4) Myosin Crossbridge attaches to another, pulls and lets it go

– *Cycle repeats as long as there is ATP

– *A-band does not change size

Review of Muscle

Structure • Large to Small: • Muscle is covered by

epimysium (which is covered by fascia) Composed Of:

• Fascicles surrounded by perimysium Composed Of:

• Muscle Fibers (Cells) surrounded by endomysium Composed Of:

• Myofibrils Composed Of:

• Filaments of actin (thin) and myosin (thick) 30

Myofibril song

31

Muscle Impulse

• Similar to nerve impulse

• Muscle stimulated to contract

• Needs neurotransmitter from neuron to

occur

– Skeletal muscles must have the

neurotransmitter acetylcholine – synthesized

in neuron’s cytoplasm

32

Muscle Contraction

33

Skeletal Muscle Activity • Functional properties:

– Irritability

• Ability to receive and

respond to stimuli

– Contractility

• Ability to shorten

34

Muscles and Nerves • Muscle must be

stimulated Neuron

(nerve cell)

• Motor neuron = nerve

cell that interacts with

muscle cells

– Can stimulate one

muscle fiber or 1000s

(usually NOT just one)

– Axon branches within

perimysium

35

Motor Unit • One neuron and the

skeletal muscle cells it

stimulates (controls)

• Neuron structure:

– Dendrites

– Cell body

– Axon

– Axon terminals

36

Motor Unit

37

Neuromuscular Junction (NMJ)

• Site where muscle and

nerve cell meet

• Each muscle cell connects

w/ a neuron’s axon

• Synaptic cleft =

• Gap between neuron and

muscle

• Neurotransmitter released

near skeletal muscle =

Acetylcholine (Ach)

38

Neuromuscular Junction

• Motor end plate – area where muscle fiber

meets neuron • Nuclei and mitochondria abundant

• Sarcolemma is folded extensively

• Neurotransmitters – contained in vesicles in

distal ends of motor neuron axons (synaptic

terminals) • Stimulate muscle fiber to contract by changing permeability of

sarcolemma

• neuromuscular juntion 40 sec 39

Neuromuscular

junction

40

Muscle Contraction

• Muscle cells

– “All or none” law of muscle contraction

– Muscle cell contracts totally not partially

• Muscles are organs made of thousands of muscle fibers (cells)

41

Muscle Twitch

• Twitch – single contraction

• very short

• Consists of :

• Stimulus

• Contraction

• Relaxation

• Latent period – delay b/w

the time the stimulus was

applied and muscle

responded

• No muscle tension

42

Muscle Twitch

• Contraction – muscle tension rises to a

peak

• Cross-bridges interacting w/ active sites

• Relaxation – muscle tension falls to

resting levels

43

Muscle Twitch

• 1 stimulation = 1 twitch

• Does not accomplish

anything useful

• Need repeated

stimulations for sustained

muscle contractions

Summation

• When individual twitches combine

• One twitch is added to another

• Second stimulus arrives before relaxation

phase has ended

45

Recruitment

• Increase in the

number of motor

units being

activated

• Muscle will

contract w/ max

tension if all are

used

46

Tetanus

• Occurs when the frequency of stimulation is

increased so that the muscle contracts without

relaxation

• 2 types:

• 1) Incomplete – muscle produces almost peak tension

• All normal muscular contractions

• 2) Complete – rate of stimulation so high muscle never relaxes

47

Tetanus – The

Disease • Caused by the bacterium Clostridium tetani

• Thrive in areas of low oxygen

• Release toxins that do not allow muscles to relax

• < 2 week incubation period

• Muscle stiffness, headache, difficulty swallowing

• Widespread muscle spasms lasting ~ 1 week

• Called “Lockjaw” bc difficult to open mouth

• 2-4 weeks, survivors recover w no aftereffects

• 40-60% mortality

• Vaccination

• 500,000 cases per year worldwide; <100 in U.S. 48

Muscle Contraction

49

Myogram

• Graph of tension

development during

a twitch

• Recorded pattern of

muscle contraction

50

Muscle Tone

• Caused by sustained contraction of certain

fibers

• Some motor units within

any muscle are always

active – even when entire

muscle is not contracting

• Caused by regular

stimulation by motor

neuron

• Important in maintaining

posture

51

Atrophy

• Muscle fibers become small and

weak

• Caused by lack of regular

stimulation

• Initially reversible

• But, dying muscle fibers are NOT

replaced

• Could become permanent

• Physical therapy is essential for those

temporarily unable to move!

• So what happens if there is no gravity?

• Preventing Muscle Atrophy in Space 7 min 52

Classification of Contractions

• 1) Isotonic – tension rises, muscle length changes

• Ex: walking, lifting object

• 2) Isometric – tension never exceeds resistance,

muscle overall does not change

• Ex: pushing against a closed door, keeping body upright to

oppose gravity

53

Rigor Mortis

54

• Few hours after death, muscles run out of ATP

• Calcium ions trigger sustained contraction

• Cross-bridges cannot detach w/out ATP

• Muscles lock in position

• All skeletal muscles involved

• Lasts ~ 15-25 hours

• Until Lysosomal enzymes breakdown myofilaments

Muscle Activity

• Must have ATP!!!!!!!!

• 1 active muscle fiber

may require 600

trillion molecules of

ATP each second!

55

Three Pathways to get ATP

• 1) Aerobic Respiration • Requires oxygen

• Makes 95% of ATP

• Occurs in mitochondria

• Fairly slow

• Glucose broken down to carbon dioxide and water

• Rich supply of ATP – 36 ATP for 1 glucose

• Occurs during light exercise

56

Three Pathways to get ATP

• 2) Anaerobic Respiration • Can continue in absence of oxygen

• Glycolysis • Yields: 2 ATP

• Occurs during intense muscle activity

• Pyruvate is converted to lactic acid

• Accumulates lactic acid which leads to muscle fatigue and soreness

57

Three Pathways to get ATP

• 3) Phosphorylation

• Changing ADP back

into ATP

• Using CP = creatine

phosphate

• Found only in muscle

cells

• Exhausted in 20

seconds

58

Muscle Fatigue

• Caused by exhaustion of

energy reserves or buildup of

lactic acid

• Takes hours for endurance

athletes

• With sudden, intense

exercise (ex: sprinting) lactic

acid increases quickly and

lowers pH of tissue

• Muscle no longer functions

59

Oxygen Debt

• Oxygen required in order

to restore normal

preexertion levels of

oxygen

• Amount of oxygen needed

to convert lactic acid to

glucose

• Breathing depth and rate

are increased until repaid

60

Types of Skeletal Muscle Fibers

• 1) Fast-twitch

• Large diameter, few mitochondria, lots of glycogen,

densely packed myofibrils

• Contract quickly (<.01 sec), powerful contractions

• Fatigue quickly

• Most fibers

61

Types of Skeletal Muscle Fibers

• 2) Slow-twitch

• 1/2 the diameter of fast-twitch

• Slow to contract (3x slower)

• Slow to fatigue

• More capillaries= more oxygen

• More mitochondria

• Have myoglobin – like

hemoglobin

• Stores oxygen in muscle

temporarily

62

White vs. Red Fibers

• White – dominated by fast

fibers

• Appear pale

• Ex: chicken breasts (“white

meat”)

• Red – dominated by slow

fibers

• Myoglobin and excessive blood

vessels cause dark color

• Ex: chicken legs (“dark meat”)

63

White vs. Red Fibers

• Humans:

• Have mix of both

• Appear pink

• No slow fibers in hands or eyes

• Back and Calf = mostly slow

• % of each genetically determined

• Can increase fatigue resistance by training

64

Anaerobic Endurance

• Contraction supported by

glycolysis and existing

energy reserves

• Quick and intense

• Muscles experience

hypertrophy – enlargement

in diameter

• # fibers does not change!

65

Aerobic Endurance

• Contraction supported

by mitochondrial

activity

• Low levels of activity

• Glucose = preferred

source of energy

• “Carb-loading” is

common

66

Cardiac Muscle - Review

• Striated

• Branched

• One nucleus

• Only in heart

• Intercalated discs connects cells

• Pacemaker cells control contractions

• Contractions last 10x longer

• Cannot undergo tetanus

• Rely on aerobic metabolism for energy

67

Smooth Muscle • Single nucleus, no striations

• 1) Multiunit– cells are

separate - NOT in “sheets”

• Does NOT contract rhythmically

– In walls of blood vessels

• 2) Visceral (single-unit) –

made of “sheets” of cells

• Cells in close contact

• Stimulate each other

– Rhythmic

– Ex: stomach, intestines, hollow

organs

68

Peristalsis

• Wavelike motion

• Occurs in tubular organs

• Caused by transmission of impulses and

rhythmicity of visceral smooth muscle

• Ex: esophagus, intestines

69

Smooth Muscle Contraction

• 2 neurotransmitters

– Acetylcholine

– Norepinephrine

• Slower to contract

than skeletal

• Maintains forceful

contraction longer

• Can stretch and

maintain pressure

– Ex: stomach, bladder 70

Muscle Attachment • Two points of attachment:

– Origin

• Point or end of muscle attached to immovable or less

movable bone

– Insertion

• Point or end of muscle attached to the movable bone

71

Muscle Movement

• Muscles only move

by contracting

– only pull

– cannot push

• Antagonistic muscles:

– Pairs of muscles

– Oppose each others

motion

• One contracts

• The other relaxes

72

Muscle Interaction

• Prime mover (agonist) –

provides most of the

movement

– Ex: deltoid

• Antagonist –resist prime

mover’s actions

– must relax

• Synergist – assist the

prime mover

• Stabilize or add pull

73

Genetics Connection – p. 186 Muscular dystrophy is caused by a missing

gene that doesn't produce the proteins

that are needed for the muscles. Each

form of muscular dystrophy is caused by

a mutated gene. (Muscular Dystrophy,

2007)

Limb-girdle muscular dystrophy

Types of MD

Duchenne Muscular Dystrophy (DMD)

Becker Muscular Dystrophy (BMD)

Emery-Dreifuss Muscular Dystrophy

(EDMD)

Limb-Girdle Muscular Dystrophy (LGMD)

Facioscapulohumeral Muscular Dystrophy

(FSMD)

Myotonic Muscular Dystrophy (MMD)

Congenital Muscular Dystrophy (CMD) 74

Major Muscles

75

Major Muscles

76

Major Muscles

77

Major Muscles

78

79

80

81

Muscles to Know

82