anatomy and physiology i muscle structure and contraction part ii instructor: mary holman

Anatomy and Physiology I

Muscle Structure and Contraction Part II

Instructor: Mary Holman

Fig. 9.2

Bone

Muscle

Epimysium

Perimysium

Endomysium

Fascicle

Fascicles

Muscle fibers (cells)

Myofibrils

Thick and thin filaments

Blood vessel

Muscle fiber

Myofibril

Sarcolemma

Nucleus

Filaments

Tendon

Fascia(covering muscle)

Axon of motorneuron

Sarcoplasmicreticulum

Actin

Myosin

Basic Skeletal Muscle Structure

Fig. 9.5a

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Sarcomere

© H.E. Huxley

16,000x

Z ZM

A bandI band I band

H zone

Three Types of Protein Associated with the Muscle Fiber

• Contractile– Actin– Myosin

• Regulatory– Troponin– Tropomyosin

• Structural– Titin– Dystrophin– Myomesin– Nebulin

Fig. 9.5b


Sarcomere

I band

Z line

I band

Z line

Thin filaments Thick filaments

A band

TitinActin Myosin

Fig. 9.6


Myosin heads - Cross-bridges

Actin moleculeTropomyosin

Thin filament

Myosinmolecule

Thickfilament

Troponin

Thick and Thin Filaments

Thin filament

Fig. 9.8c


Mitochondria

Acetylcholine

Synapticvesicles

Synapticcleft

Neuromuscular Junction

Foldedsarcolemma


Motor neuronof motor unit 2


Skeletal musclefibers

Branches ofmotor neuronaxon

Muscle Fibers innervated by Two Motor Neurons

Events Leading up to Muscle Contraction• Nerve impulse arrives at end of motor nerve axon causing• Acetylcholine (Ach) release into synapse via exocytosis• ACh floods across synaptic gap and attaches to receptors on the sarcolemma• Permeability of sarcolemma changes and Na+ enters cell• A muscle impulse is triggered • Muscle impulse travels via the transverse tubules throughout muscle cell• Ca++ diffuses from SR and binds to troponin on actin• Myosin cross bridges link with actin and muscle contracts

Fig. 9.9a


Actin monomers

Tropomyosin

Troponin

Thick filament

Thin filament

Relaxed muscle

1

ADP + P ADP + P

Muscle contraction begins and continues ifATP is available and Ca++ level in the sarcoplasm is high

Fig. 9b


Tropomyosin pulled aside

ATP

2

Ca+2 binds to troponin

Binding sites onactin exposed

Ca+2 Ca+2 Ca+2

Exposed binding sites on actin moleculesallow the muscle contraction cycle to occur

ADP + P ADP + P

Muscle Contraction Ca++ released from sarcoplasmic reticulum

Fig. 9.9c

3

ADP + P ADP + P

PADP

PADP

Cross-bridges pull thin filament (power stroke),ADP and P released from myosin

ADP + P

4

Myosin heads bind to actin, forming cross-bridges

ATP

ATP ATP ATP

New ATP binds to myosin, releasing linkages5

6 ATP splits, which provides power to“cock” the myosin cross-bridges

ADP + P ADP + P

Fig. 9.10a


Z line Z line

Sarcomere

Contracting

Fully contracted

Relaxed

2

3

1

A band

Thinfilaments

Thickfilaments

Fig. 9.10b


Z line Z line

Sarcomere

A band

© H.E. Huxley

EM 23,000x

Muscle Fiber Excitation

• Nerve impulse arrives at axon terminal• Triggers release of Ach by exocytosis• ACh diffuses across synaptic cleft• ACh binds to receptors on muscle motor end plate• Sarcolemma becomes more permeable to Na+• Na+ triggers release of muscle action potential• Muscle action potential travels along outside of

sarcolemma and into T tubules

• Action potential triggers Ca++ release from SR• Ca++ binds to troponin on thin filament • Tropomyosin is pulled aside, revealing binding sites

• Myosin links to & pulls actin to contract muscle

Muscle Fiber Relaxation• Acetylcholinesterase decomposes ACh in synapse• Action potential (impulse) ends• SR actively pumps Ca++ back into SR• Tropomyosin moves back to cover binding sites• Myosin heads detach• Muscle fiber returns to its longer resting length

Part II

Muscle Metabolism

Muscle Responses

Smooth and Cardiac Muscle

Text pgs 302 - 313

Fig. 9.11


ADP

ATP

ATP

P

When cellular

Creatine

Creatine

ADP

ATP

ATP

P

is high

Creatine

Creatine

When cellular is low

Energy Sources for Muscular Contraction

Immediate ATP from creatine phosphate

AATPATP ATP

Creatinephosphate

ADP ADP

Creatine

Relaxed muscle

Contractingmuscle

Energy formuscle contraction

P


EnergyNet gain

2 Lactic acid

Glucose

2 Pyruvic acid

Short-term ATP from Anaerobic Respiration

2 ATP

Or From blood

Into blood

Muscle glycogen

Fig. 9.12


Lactic acid

ATPSynthesis of 34CO2 + H2O + Energy

Pyruvic acid

Heat

Mit

och

on

dri

aC

yto

so

l

Citric acidcycle

Electrontransport

chain

Oxygen carried fromthe lungs byhemoglobin in redblood cells is storedin muscle cells bymyoglobin and isavailable to supportaerobic respiration.

Long-term ATP is provided by Aerobic Cellular Respiration

Heat Production• 85% of heat generated in the body is

from muscle contraction

Muscle Fatigue• Defined as a loss of work out-putleading to reduced performance

• Build-up of lactic acid• Depletion of muscle glycogen• Decrease in blood glucose• Increase in body temperature

Oxygen Debt

Recovery period - restores pre-exertion metabolic condition

• convert lactic acid back into glycogen

• resynthesize creatine phosphate

• replenish oxygen storage in myoglobin

Fig. 9.14

Fo

rce

of

con

trac

tio

n

Time

Latentperiod

Period ofcontraction

Period ofrelaxation

Time ofstimulation

Myogram of a single muscle twitch

Fig. 9.15


(b) Overly shortened (c) Overly stretched

(a) Optimal length

Muscle fiber length

Fo

rce

Force vs Muscle fiber length

Fig. 9.16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Time

(c)

(b)

Fo

rce

of

con

trac

tio

n(a)

Fo

rce

of

con

trac

tio

nF

orc

e o

fco

ntr

acti

on

Increasing Stimulation Frequency

Fast Twitch and Slow Twitch Muscle Fibers

Slow-twitch fibers (Type I)Slow to respond, slow to fatigue

Fast-twitch glycolytic fibers (Type IIa)Fast to respond, fast to fatigue

Fast-twitch fatigue-resistant fibers (Type IIb)Fast to respond, slow to fatigue

Slow-twitch fibers (Type I)Slow to respond - slow to fatigue• Always oxidative • Resistant to fatigue• Red fibers • Most myoglobin• Good blood supply - more capillaries• Lots of mitochondria • Smallest fibers

Fast-twitch glycolytic fibers (Type IIa)Fast to respond - fast to fatique• White fibers (less myoglobin)• Poorer blood supply• Susceptible to fatigue• Largest fibers• Lots of glycogen• Few mitochondria

Fast-twitch fatigue-resistant fibers (Type IIb)Fast to respond - slow to fatique• Intermediate fibers• Oxidative• Intermediate amount of myoglobin• Intermediate amount of mitochondria• Pink to red in color• Resistant to fatigue




Skeletal musclefibers

Branches ofmotor neuronaxon

Muscle Fibers innervated by Two Motor NeuronsFig 9.17

Fig. 9.18


Movement Movement

(a) Muscle contracts with force greater than resistance and shortens (concentric contraction)

(c) Muscle contracts but does not change length (isometric contraction)

(b) Muscle contracts with force less than resistance and lengthens (eccentric contraction)

Nomovement

IsometricEccentricConcentric

Isotonic

Types of Muscle Tissue

• General characteristics:• Muscle cells also called muscle fibers• Contractile• Three (3) types:

• Skeletal muscle• Smooth muscle• Cardiac muscle

• Skeletal muscle• Attached to bones• Striated• Voluntary

• Smooth muscle• Walls of organs• Skin• Walls of blood vessels• Involuntary• Non-striated

• Cardiac muscle • Heart wall• Involuntary• Striated• Intercalated discs

Fig. 5.28

Striations

Portion of amuscle fiber

Nuclei

(a) (b)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Skeletal Muscle Tissue

Fig. 5.29

Nucleus

Cytoplasm

(a) (b)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer

Smooth Muscle Tissue

Smooth Muscle Contraction

From: Principles of Anatomy & Physiology Tortora & Grabowsky

Fig. 5.30

Intercalateddisc

Nucleus

Striations

(a)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or

display

b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Cardiac Muscle Cells

desmosome

gap junction

Fig. 9.20a


Resistance Force (Effort)Force(Effort)

Fulcrum

Resistance

Fulcrum

First-Class Lever EFR

Fig. 9.20b


FulcrumForce Effort Force Effort

Resistance Resistance

Fulcrum

Second-class LeverFRE

Fig. 9.20c


Force - Effort

ResistanceForceEffort

Fulcrum

Third-class lever

Resistance

Fulcrum

FER

Fig. 9.22


Radius

Coracoid process

Origins ofbiceps brachii

Tendon oflong head

Tendon ofshort head

Bicepsbrachii

Insertion ofbiceps brachii

Origin = Stable bone

Insertion =Moveable bone

anatomy and physiology i muscle structure and contraction part ii instructor: mary holman

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