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 Terms Related to Muscles Tendon Fascia Aponeurosis Epimysium Perimysium Endomysium

Skeletal Muscle Aponeuroses muscle to muscle Skeletal muscles Tendons Fig. 9.1 Aponeuroses Skeletal Muscle muscle to muscle Skeletal muscles Tendons muscle to bone Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Thick and thin filaments Fig. 9.2d Surrounded by Muscle Fascia Epimysium Fascicles Perimysium Muscle fibers (cells) Endomysium Myofibrils Actin & Myosin Thick and thin filaments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Attachment of Muscle to Bone Fascicle Tendon Fascia (covering muscle) Fig. 9.2a Attachment of Muscle to Bone Tendon Fascia (covering muscle) Epimysium Perimysium Endomysium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fascicle

Fascicle of Skeletal Muscle Fig. 9.2b Fascicle of Skeletal Muscle Perimysium Fascicle Endomysium Axon of motor neuron Sarcolemma Blood vessel Nucleus Muscle fiber (Cell) Sarcoplasmic reticulum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Skeletal Muscle Fiber - The Muscle Cell Fig. 9.2c Skeletal Muscle Fiber - The Muscle Cell Sarcoplasmic reticulum Nucleus Myofibril Filaments Sarcolemma Note:This slide does not show SR surrounding each myofibril! Fig 9.4 more accurate. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

SEM of a Fascicle (cross section) Fig. 9.3 SEM of a Fascicle (cross section) Perimysium Fascicle Endomysium Muscle fiber Nucleus Myofibrils 320X © Ed Reschke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© The McGraw-Hill Companies, Inc./Al Telser, photographer Fig. 5.28 Skeletal Muscle Tissue 700x Nuclei Portion of a muscle fiber © The McGraw-Hill Companies, Inc./Al Telser, photographer Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

© CNRI/SPL/Photo Researchers, Inc. Page 294 Human Striated Muscle Tissue SEM 3000x One sarcomere Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © CNRI/SPL/Photo Researchers, Inc.

16,000x Sarcomere Fig. 9.5a © H.E. Huxley Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Thick and Thin filaments of the Myofibril Fig. 9.4a Thick and Thin filaments of the Myofibril

Z Z Sarcomere M H 16,000x zone I band A band I band Fig. 9.5a © H.E. Huxley Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Sarcomere Titin Actin Myosin Fig. 9.5b A band I band I band Z line Thin filaments Thick filaments Actin Myosin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Three Types of Protein Associated with the Muscle Fiber Contractile Actin Myosin Regulatory Troponin Tropomyosin Structural Titin Dystrophin Myomesin Nebulin

Thick and Thin Filaments Fig. 9.6 Thick and Thin Filaments Myosin heads which form bridges to Actin Thin filament Thick filament Thin filament Myosin molecule Actin molecule Troponin Tropomyosin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Sarcoplasmic Reticulum and Transverse Tubules Fig. 9.7 Sarcoplasmic Reticulum and Transverse Tubules Myofibrils Cisternae of sarcoplasmic reticulum Triad Nucleus Transverse tubule Sarcoplasmic reticulum Openings into transverse tubules Mitochondria Nucleus Thick and thin filaments Sarcolemma Sarcoplasm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Neuro- Muscular Junction ( NMJ ) Fig. 9.8a Synaptic vesicles Mitochondria Motor neuron axon Acetylcholine Synaptic cleft Folded sarcolemma Axon branches Motor end plate Muscle fiber nucleus Myofibril of muscle fiber Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Neuromuscular Junction Fig. 9.8c Neuromuscular Junction Motor neuron Synaptic end bulb Synapse Muscle cell Motor end plate Synaptic vesicles Mitochondria Synaptic cleft Acetylcholine Folded sarcolemma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Neuromuscular Junction Fig. 9.8b Neuromuscular Junction Motor neuron axon Muscle fiber Neuromuscular junction 500x © McGraw-Hill Higher Education, Inc./Carol D. Jacobson Ph.D., Dept. Veterinary Anatomy, Iowa State University Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Muscle Fibers innervated by Two Motor Neurons of motor unit 2 Motor neuron of motor unit 1 Branches of motor neuron axon Skeletal muscle fibers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Muscle Fibers innervated by Two Motor Neurons of motor unit 2 Motor neuron of motor unit 1 Branches of motor neuron axon Skeletal muscle fibers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Neuromuscular Junction SEM 1650x From: Principles of Anatomy & Physiology Tortora & Grabowsky

Events Leading up to Muscle Contraction NMJ 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 Muscle fiber

Sliding Filament Theory Fig. 9.9 Sliding Filament Theory Relaxed muscle Tropomyosin Troponin Thin filament Actin Actin monomers ADP + P ADP + P Thick filament - Myosin 1 Muscle contraction begins and continues if ATP is available and Ca++ level in the sarcoplasm is high Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Ca++ released from sarcoplasmic reticulum Fig. 9.9 Muscle Contraction Ca++ released from sarcoplasmic reticulum Ca+2 binds to troponin Tropomyosin pulled aside ATP Binding sites on actin exposed Ca+2 Ca+2 Ca+2 ADP + P ADP + P 2 Exposed binding sites on actin molecules allow the muscle contraction cycle to occur Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 9.9 ADP + P ADP + P 3 Myosin heads bind to actin forming cross-bridges ADP ADP P P ADP + P 4 Cross-bridges pull thin filament (power stroke), ADP and P released from myosin

6 ADP + P ADP + P ATP ATP ATP ATP Fig. 9.9 ATP ATP ATP ATP New ATP binds to myosin, releasing linkages 5 ADP + P ADP + P 6 ATP splits, which provides power to“cock” the myosin cross-bridges

Fig. 9.10a Relaxed Contracting Fully contracted Sarcomere 1 2 3 A band Z line Z line 1 Relaxed Thin filaments Thick filaments 2 Contracting 3 Fully contracted Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Contracting Sarcomere Fig. 9.10b Contracting Sarcomere A band Z line Z line © H.E. Huxley Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Action potential triggers Ca++ release from SR 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