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 motor neuron Sarcoplasmic reticulum 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 Z M A bandI 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sarcomere I band Z line I band Z line Thin filamentsThick filaments A band Titin ActinMyosin

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

Fig. 9.8c Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondria Acetylcholine Synaptic vesicles Synaptic cleft Neuromuscular Junction Folded sarcolemma

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron of motor unit 2 Motor neuron of motor unit 1 Skeletal muscle fibers Branches of motor neuron axon 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Actin monomers Tropomyosin Troponin Thick filament Thin filament Relaxed muscle 1 ADP +P P Muscle contraction begins and continues if ATP is available and Ca ++ level in the sarcoplasm is high

Fig. 9b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tropomyosin pulled aside ATP 2 Ca +2 binds to troponin Binding sites on actin exposed Ca +2 Exposed binding sites on actin molecules allow the muscle contraction cycle to occur ADP +P P Muscle Contraction Ca ++ released from sarcoplasmic reticulum

Fig. 9.9c 3 ADP + P P P ADP P 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 New ATP binds to myosin, releasing linkages5 6 ATP splits, which provides power to“cock” the myosin cross-bridges ADP + P P

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

Fig. 9.10b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ADP ATP P When cellular Creatine ADP ATP P is high Creatine When cellular is low Energy Sources for Muscular Contraction

Immediate ATP from creatine phosphate AATP ATP Creatine phosphate ADP Creatine Relaxed muscle Contracting muscle Energy for muscle contraction P

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy Net gain 2 Lactic acid Glucose 2 Pyruvic acid Short-term ATP from Anaerobic Respiration 2 ATP Or From blood Into blood Muscle glycogen

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactic acid ATP Synthesis of 34 CO 2 + H 2 O + Energy Pyruvic acid Heat Mitochondria Cytosol Citric acid cycle Electron transport chain Oxygen carried from the lungs by hemoglobin in red blood cells is stored in muscle cells by myoglobin and is available to support aerobic 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-put leading 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 Force of contraction Time Latent period Period of contraction Period of relaxation Time of stimulation Myogram of a single muscle twitch

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) Overly shortened(c) Overly stretched (a) Optimal length Muscle fiber length Force Force vs Muscle fiber length

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Time (c) (b) Force of contraction (a) Force of contraction Force of contraction 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron of motor unit 2 Motor neuron of motor unit 1 Skeletal muscle fibers Branches of motor neuron axon Muscle Fibers innervated by Two Motor Neurons Fig 9.17

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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) No movement 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 Striations Portion of a muscle 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 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 Intercalated disc 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ResistanceForce (Effort) Force (Effort) Fulcrum Resistance Fulcrum First-Class Lever EFR

Fig. 9.20b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fulcrum Force Effort Resistance Fulcrum Second-class Lever FRE

Fig. 9.20c Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Force - Effort Resistance Force Effort Fulcrum Third-class lever Resistance Fulcrum FER

Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radius Coracoid process Origins of biceps brachii Tendon of long head Tendon of short head Biceps brachii Insertion of biceps brachii Origin = Stable bone Insertion = Moveable bone