Anatomy and Physiology I Muscle Structure and Contraction Instructor: Mary Holman

Anatomy and Physiology I

Muscle Structure and Contraction

Instructor: Mary Holman

Muscle Functions

• Produce body movements

• Stabilize body position

• Regulate organ volume

• Move fluids and solid food and wastes in the body

• Produce heat

Properties of Muscle Tissue

• Electrical excitability

• Contractility

• Extensibility

• Elasticity

Connective Tissue TermsRelated to Muscles

Tendon

Fascia

Aponeurosis

Epimysium

Perimysium

Endomysium

Fig. 9.1

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

Aponeuroses

Skeletal muscles

Tendons

muscle to muscle

muscle to bone

Skeletal Muscle

Fig. 9.2d


Muscle

Fascicles

Muscle fibers (cells)

Myofibrils

Thick and thin filamentsActin &Myosin

FasciaEpimysium

Perimysium

Endomysium

Surrounded by

Fig. 9.2a


EpimysiumPerimysium

Endomysium

Tendon

Fascia(covering muscle)

Attachment of Muscle to Bone

Fascicle

Fig. 9.2b

Perimysium

EndomysiumAxon of motorneuron

Fascicle

Blood vessel

Muscle fiber(Cell)

Sarcolemma

Nucleus


Sarcoplasmicreticulum

Fascicle of Skeletal Muscle

Fig. 9.2c


MyofibrilNucleus FilamentsSarcoplasmicreticulum

Skeletal Muscle Fiber - The Muscle Cell

Sarcolemma

Note:This slide does not show SR surrounding each myofibril! Fig 9.4 more accurate.

Fig. 9.3


Fascicle

Perimysium

Endomysium

Muscle fiber

Nucleus

Myofibrils

© Ed Reschke 320X

SEM of a Fascicle (cross section)

Portion of amuscle fiber

Nuclei

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

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

Skeletal Muscle Tissue 700xFig. 5.28

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © CNRI/SPL/Photo Researchers, Inc.

SEM 3000x

Human Striated Muscle TissuePage 294

One sarcomere

Fig. 9.5a


Sarcomere© H.E. Huxley

16,000x

Fig. 9.4a

Thick and Thin filaments of the Myofibril

Fig. 9.5a


Sarcomere

© H.E. Huxley

16,000x

Z ZM

A bandI band I band

H zone

Fig. 9.5b


Sarcomere

I band

Z line

I band

Z line

Thin filaments Thick filaments

A band

TitinActin Myosin

Three Types of Protein Associated with the Muscle Fiber

• Contractile– Actin– Myosin

• Regulatory– Troponin– Tropomyosin

• Structural– Titin– Dystrophin– Myomesin– Nebulin

Fig. 9.6


Myosin heads which form bridges to Actin

Actin moleculeTropomyosin

Thin filament

Myosinmolecule

Thickfilament

Troponin

Thick and Thin Filaments

Thin filament

Fig. 9.7


Nucleus

Mitochondria

Sarcolemma

Sarcoplasm

Nucleus

Myofibrils

Sarcoplasmicreticulum

Openings intotransverse tubules

Thick and thinfilaments

Cisternae ofsarcoplasmic reticulum

Transverse tubule

Triad

Sarcoplasmic Reticulum and Transverse Tubules

Fig. 9.8a


Axon branches

Mitochondria

Acetylcholine

Synapticvesicles

Synapticcleft

Foldedsarcolemma

Motorend plate

Myofibril ofmuscle fiber

Muscle fibernucleus

Motorneuron axon

TheNeuro-MuscularJunction( NMJ )

Fig. 9.8c


Mitochondria

Acetylcholine

Synapticvesicles

Synapticcleft

Neuromuscular Junction

Foldedsarcolemma

Motor neuronSynaptic end bulb

Synapse

Muscle cellMotor end plate

Fig. 9.8b


Motor neuron axon

Muscle fiber

Neuromuscular junction

© McGraw-Hill Higher Education, Inc./Carol D. Jacobson Ph.D., Dept. Veterinary Anatomy, Iowa State University 500x



Motor neuronof motor unit 2


Skeletal musclefibers

Branches ofmotor neuronaxon

Muscle Fibers innervated by Two Motor Neurons




Skeletal musclefibers

Branches ofmotor neuronaxon

Muscle Fibers innervated by Two Motor Neurons

From: Principles of Anatomy & Physiology Tortora & Grabowsky


SEM 1650x

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 the muscle cell• Ca++ diffuses from SR and binds to troponin on actin• Myosin cross bridges link with actin and muscle contracts

NMJ

Muscle fiber

Fig. 9.9


Actin monomers

Tropomyosin

Troponin

Thick filament - Myosin

Thin filamentActin

Relaxed muscle

1

ADP + P ADP + P

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

Sliding Filament Theory

Fig. 9.9


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. 9.9

3 Myosin heads bind to actin forming cross-bridges

ADP + P ADP + P

PADP

PADP

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

ADP + P

4

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. 9.9

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

Contracting Sarcomere

A band

© H.E. Huxley

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

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Anatomy and Physiology I Muscle Structure and Contraction Instructor: Mary Holman