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Muscles and Muscle Tissue Chapter 9

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Overview of Muscle Tissues • Compare and Contrast the three basic types of muscle tissue

• List four important functions of muscle tissue

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Muscle Terminology • Muscle Fibers (skeletal and smooth muscle cells) • Myo and sarco = muscle • Sacroplasm, sarcolemma

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Types of Muscle Tissue • Skeletal Muscle

•  Longest muscle cells •  Striated •  Voluntary muscle •  Very powerful, easily

fatigued •  Highly adaptable

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Types of Muscle Tissue • Cardiac Muscle

•  Striated •  Involuntarily controlled •  Connected by intercalated

discs •  Can contract without any

nervous system input

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Types of Muscle Tissue • Smooth Muscle

•  Found in walls of hollow organs •  Elongated cells •  No striations •  Involuntary •  Slow sustained contractions

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Special Characteristics of Muscle Tissue • 1. Excitability • 2. Contractility • 3. Extensibility • 4. Elasticity

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Muscle Functions • Movement Production • Maintain Posture and Body Position

• Joint Stabilization • Heat Generation

• Additional Functions •  Organ Protection •  Valve formation •  Pupil constriction

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Check Your Understanding • When describing muscle, what does striated mean? • Andrew is pondering an exam question that asks, Which muscle type has elongated cells and is found in the walls of the urinary bladder? How should he respond Reed?

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Skeletal Muscle • Describe the Gross Structure of a Skeletal Muscle • Describe the microscopic structure and functional roles of the myofibrils, sarcoplasmic reticulum, and T tubules of skeletal muscle fibers

• Describe the sliding filament model of muscle contraction

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Gross Anatomy of a Skeletal Muscle • Each muscle is a discrete

organ • Nerve and Blood supply • Connective Tissue Sheaths

•  Epimysium •  Perimysium and fascicles •  Endomysium

• Attachments •  Direct/Fleshy Attachments •  Indirect Attachments

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Microscopic Anatomy of a Skeletal Muscle Fiber (Cell) • Sarcolemma • Multinucleate • Sarcoplasm

•  Glycosomes •  Myoglobin

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Microscopic Anatomy of a Skeletal Muscle Fiber • Myofibrils

• Striations, Sarcomeres, and Myofilaments. •  Dark A Bands

•  H Zone •  M Line

•  Light I Bands •  Z Disc

•  Sarcomeres

•  Myofilaments •  Thick Filaments (myosin) •  Thin Filaments (actin)

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Molecular Composition of Myofilaments • Thick Filaments

•  Myosin •  Elastic Filaments (Titin)

• Thin Filaments •  Actin •  Tropomyosin •  Troponin

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Sarcoplasmic Reticulum and T-Tubules

• Sarcoplasmic Reticulum (SR) •  Most tubules run

longitudinully •  Terminal Cistern Pairs

• T-Tubules •  Continuous with the

extracellular fluid •  Form Triads with the

terminal cistern pairs •  Extension of the

sarcolemma

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Sliding Filament Model of Contraction •  In a relaxed muscle fiber,

thick and thin filaments overlap only at the ends of the A band.

• The sliding filament model states that during contraction, the thin filaments slide past the thick filaments so that the actin and myosin filaments overlap to a greater degree.

• Pg. 285

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•  http://www.youtube.com/watch?v=Ct8AbZn_A8A

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Check Your Understanding • How does the Term Epimysium relate to the role and

position of this connective tissue sheath? • Which Myofilaments have binding sites for calcium? What

specific molecule binds calcium? • Which region or organelle -cytosol, mitochondrion, or SR-

contains the highest concentration of calcium ions in a resting muscle fiber? Which structure provides the ATP needed for muscle activity?

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Physiology of Skeletal Muscle Fibers • Explain how muscle fibers are stimulated to contract by

describing events that occur at the neuromuscular junction. • Describe how an Action Potential is Generated • Follow the events of excitation-contraction coupling that

lead to cross bridge activity.

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Activation and Excitation-Contraction Coupling • Activation

•  Step 1: The fiber must be activated, that is, stimulated by a nerve ending so that a change in membrane potential occurs.

•  Step 2: Next, it must generate an electrical current, called an action potential, in its sarcolemma.

• Excitation-Contraction Coupling •  Step 3: The action potential is

automatically propagated along the sarcolemma.

•  Step 4: Then, intracellular calcium ion levels must rise briefly, providing the final trigger for contraction.

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The Nerve Stimulus and Events at the NMJ NMJatatheNMJ •  Somatic Motor Neurons •  Neuromuscular Junction •  Synaptic Cleft •  Synaptic Vesicles (ACh)

•  How does a motor neuron stimulate a skeletal muscle fiber? •  Step 1: When a nerve impulse reaches

the end of an axon, the axon terminal releases ACH into the synaptic cleft

•  Step 2: ACh diffuses across the cleft and attaches to ACh receptors on the sarcolemma of the muscle fiber.

•  Step 3: ACh binding triggers electrical events that ultimately generate an action potential

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Generation of an Active Potential Across the Sarcolemma

• Action Potential: The predictable sequence of electrical changes across a membrane.

• Step 1: Generation of an end plate potential

• Step 2: Depolarization: Generation and Propagation of an action potential

• Step 3: Repolarization: Restoring the Sarcolemma to its original state

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Excitation-Contraction Coupling • Step 1: Action Potential Propagation • Step 2: Calcium ion release • Step 3: Calcium binds to Troponin and removes the

blocking action of tropomyosin • Step 4: Contraction Begins

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Cross Bridge Cycling •  http://www.youtube.com/watch?v=Ct8AbZn_A8A

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Check Your Understanding • What are the three structural components of a

neuromuscular junction? • What is the final trigger for contraction? What is the initial

trigger? • What prevents the filaments from sliding back to their

original position each time a myosin cross bridge detaches from actin?

• What would happen if a muscle fiber suddenly ran out of ATP when sarcomeres had only partially contracted?

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Contraction of Skeletal Muscle • Define motor unit and muscle twitch, and describe the

events occurring during the three phases of muscle twitch. • Explain how smooth, graded contractions of a skeletal

muscle are produced. • Differentiate between isometric and isotonic contractions.

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Types of Muscle Contraction • Muscle tension versus load •  Isometric versus isotonic

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The Motor Unit • One motor neuron and all of its innervated fibers •  Innervated fibers are spread throughout entire muscle

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The Muscle Twitch • The motor units response to a single action potential from

its motor neuron •  3 Phases of a twitch myogram

•  Phase 1: Latent Period •  Phase 2: Period of Contraction •  Phase 3: Period of Relaxation

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Graded Muscle Responses • Can be Graded in two ways

•  1.) By changing the frequency of stimulation •  Temporal summation •  unfused (incomplete) tetanus •  fused (complete) tetanus

•  2.) By changing the strength of stimulation •  Recruitment (multiple motor unit summation)

•  Sub threshold stimuli •  threshold stimulus •  maximal stimulus

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Size Principle • The motor units with the smallest muscle fibers are activated

first • As motor units with larger and larger muscle fibers begin to

be excited, contractile strength increases. • The largest motor units are only activated when maximal

contraction is required.

• Prevents fatigue due to asynchronous contraction

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Isotonic and Isometric Contractions •  Isotonic: Muscle length

changes •  Concentric: Muscle

shortens •  Eccentric: Muscle

Lengthens

•  Isometric: Muscle length does not change

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Check your understanding • What is a motor unit • What is happening in a muscle during the latent period of a

twitch contraction? • Matt is competing in a chin up competition, What type of

muscle contractions are occurring in his biceps muscles?

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Muscle Metabolism • Describe three ways in which ATP is regenerated during

skeletal muscle contraction. • Define EPOC and muscle fatigue. List possible causes of

muscle fatigue.

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Providing Energy for Muscle Contraction

• ATP is the only energy source used directly for contractile activities

• Muscles store only 4-6 seconds worth • Therefore ADP must be converted to ATP as quickly as

ATP is used as energy •  3 Pathways

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Pathway #1 • Direct Phosphorylation of ADP by Creatine Phosphate

•  Creatine Phosphate + ADP -----------> Creatine + ATP •  Pathway is viable for roughly 15 seconds

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Pathway #2 • Anaerobic Pathway: Glycolysis and Lactic Acid Formation

•  Glucose is broken down in to two Pyruvic acid molecules releasing 2 ATP molecules

•  Glycolysis occurs both in the presence and absence of oxygen •  Viable as a primary energy source for 30-40 seconds •  Ordinarily the pyruvic acid byproducts enter the mitochondria for further

metabolism •  However At 70% maximal contractile activity blood vessels are compressed

preventing aerobic mitochondrial metabolism. •  Under these circumstances (anaerobic glycolysis) most of the pyruvic acid is

converted to lactic acid

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Pathway #3 • Aerobic Respiration

•  During rest, light, and moderate exercise, this pathway provides 95% of ATP supply.

•  Occurs in the mitochondria •  Requires oxygen •  Glucose + Oxygen --------> Carbon Dioxide +

water + 32 ATP •  Slowest of three systems •  Fuel source progression:

•  1. Muscle Glycogen •  2. Bloodborne glucose, pyruvic acid, free fatty

acids •  3. After 30 minutes, free fatty acids are the

primary source of fuel

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Energy Systems During Sport • Aerobic Endurance • Anaerobic Threshold

• Weightlifting: Direct Phosphorylation

• On off activities such as tennis, soccer, 100m swim: Anaerobic

• Prolonged jogging: Aerobic

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Muscle Fatigue • Physiological inability to contract in the presence of stimuli • Caused by ionic disturbances that alter E-C coupling

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Excess Post-exercise Oxygen Consumption (EPOC) • Post exercise, muscle tissue must

•  replenish its myoglobin bound oxygen reserves •  convert excess lactic acid into pyruvic acid •  replace glycogen stores •  Resynthesize ATP and creatine phosphate reserves

• The increased oxygen demand during this recovery period is referred to as the EPOC or oxygen debt

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Heat Production • Only 40% of energy used during muscle contraction is

converted into useful work •  60% is converted into heat

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Check Your Understanding • Clayton has just finished jogging and is breathing heavily.

Why is Clayton breathing heavily? What metabolic product might account for his sore muscles and muscle weakness?

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Forces of Muscle Contraction • Describe factors that influence the force, velocity, and

duration of skeletal muscle contraction • Describe three types of skeletal muscle fibers and explain

the relative value of each type

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Muscle Contraction Force •  Influencing Factors

•  Number of fibers recruited •  Size of muscle fibers •  Frequency of stimulation •  Degree of muscle stretch

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Velocity and Duration of Contraction •  Influencing factors

•  Muscle Fiber Type •  Load •  Recruitment

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Muscle Fiber Type • Classified based on two criteria

•  Speed of contraction •  Slow fibers •  Fast Fibers

•  Major pathways for forming ATP •  Glycolytic •  Oxidative

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3 Fiber Types • Slow Oxidative

• Fast Oxidative

• Fast Glycolytic

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Load • Greater load results in

•  a longer latent period •  a slower contraction •  a shorter duration of muscle contraction

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Recruitment • The greater number of motor units recruited

•  The faster the contraction •  The more prolonged the contraction

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Check Your Understanding •  List two factors that influence contractile force and two that

influence velocity of contraction

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Adaptations to Exercise • Compare and Contrast the effects of aerobic and

resistance exercise on skeletal muscles and on other body systems

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Aerobic (endurance) Exercise • Number of capillaries surrounding the muscle fibers

increases • Number of mitochondria within the muscle fibers increases • Concentration of myoglobin increases

• Affects all fiber types, conversion is possible

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Resistance Exercise • Causes muscle hypertrophy • Muscle fibers increase in diameter, not number

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Study guide

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