Introduction to Muscular Tissue
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Questions and Answers

What type of muscle tissue is responsible for stabilizing body positions?

  • Smooth muscle tissue
  • Connective tissue
  • Cardiac muscle tissue
  • Skeletal muscle tissue (correct)

    • Which property allows muscular tissue to generate electrical signals?

  • Elasticity
  • Extensibility
  • Excitability (correct)
  • Contractility

    • What is the primary function of cardiac muscle tissue?

  • Regulate body temperature
  • Move blood through the heart (correct)
  • Stabilize body positions
  • Assist in digestion

    • Which layer of connective tissue wraps around individual fascicles?

    <p>Perimysium</p> Signup and view all the answers

    What is a key characteristic of smooth muscle tissue?

    <p>It regulates passage of substances</p> Signup and view all the answers

    What does extensibility in muscular tissue refer to?

    <p>The ability to stretch without tearing</p> Signup and view all the answers

    Muscle fibres are organized into bundles referred to as what?

    <p>Fascicles</p> Signup and view all the answers

    Which of the following muscle tissues generates heat during contraction?

    <p>All types of muscle tissues</p> Signup and view all the answers

    What is the primary reason muscles need oxygen after exercise?

    <p>To replenish myoglobin</p> Signup and view all the answers

    Which type of muscle fiber is characterized by a high amount of myoglobin and fatigue resistance?

    <p>Slow oxidative fibers</p> Signup and view all the answers

    What is the metabolic mode primarily used by slow oxidative fibers?

    <p>Aerobic respiration</p> Signup and view all the answers

    What term describes the period when oxygen levels are insufficient during exercise leading to a deficit?

    <p>Oxygen debt</p> Signup and view all the answers

    Fast oxidative-glycolytic fibers are characterized by which of the following?

    <p>They are dark red and largest in size.</p> Signup and view all the answers

    What type of fibers predominantly make up the endomysium?

    <p>Reticular fibers</p> Signup and view all the answers

    What connects muscles to bones as a thick rope-like structure?

    <p>Tendons</p> Signup and view all the answers

    Which type of motor neurons regulate voluntary muscle contraction?

    <p>Somatic motor neurons</p> Signup and view all the answers

    What is the term for the mature cells formed from myoblasts?

    <p>Myocytes</p> Signup and view all the answers

    Which structure in muscle cells serves as the plasma membrane?

    <p>Sacrolemma</p> Signup and view all the answers

    What carbohydrate energy store is found densely packed within the sarcoplasm?

    <p>Glycogen</p> Signup and view all the answers

    What is the function of myoglobin in muscle cells?

    <p>Binds oxygen</p> Signup and view all the answers

    What defines a triad in the context of muscle cells?

    <p>Two terminal cisternae and one T-tubule</p> Signup and view all the answers

    What are the thick filaments in a sarcomere primarily composed of?

    <p>Myosin</p> Signup and view all the answers

    What is the role of troponin in muscle contraction?

    <p>Binds calcium</p> Signup and view all the answers

    What type of proteins stabilize and connect the sarcomere?

    <p>Structural proteins</p> Signup and view all the answers

    What is muscular hypertrophy primarily a response to?

    <p>Increased mechanical stress</p> Signup and view all the answers

    What type of respiratory process do skeletal muscles require for function?

    <p>Aerobic cellular respiration</p> Signup and view all the answers

    The overlapping pattern of filaments in muscle produces which appearance?

    <p>Striated appearance</p> Signup and view all the answers

    What happens to the length of the filaments during the contraction of a sarcomere?

    <p>The thin and thick filaments do not change in length.</p> Signup and view all the answers

    Which step in the contraction cycle involves myosin pulling the thin filaments toward the M-line?

    <p>The power stroke.</p> Signup and view all the answers

    What obscures the myosin-binding sites on the thin filaments?

    <p>Tropomyosin.</p> Signup and view all the answers

    What is required for myosin to release thin filaments during muscle contraction?

    <p>New ATP molecule.</p> Signup and view all the answers

    What happens to the I band during muscle contraction?

    <p>It narrows.</p> Signup and view all the answers

    In terms of filament overlap, what happens if thick and thin filaments completely overlap at rest?

    <p>No tension is generated.</p> Signup and view all the answers

    Which type of neuron stimulates muscle fibers at the neuromuscular junction?

    <p>Somatic motor neurons.</p> Signup and view all the answers

    What is the initial change in membrane potential during an action potential called?

    <p>Depolarization.</p> Signup and view all the answers

    What problem arises if the length of a sarcomere is too short?

    <p>No room for thin filaments to slide.</p> Signup and view all the answers

    Which channels are responsible for repolarization during the action potential?

    <p>Voltage-gated potassium channels.</p> Signup and view all the answers

    What is the role of neurotransmitters like acetylcholine at the neuromuscular junction?

    <p>They bind to receptors and stimulate action potentials.</p> Signup and view all the answers

    What occurs when voltage-gated calcium channels open at T-tubules during muscle contraction?

    <p>Calcium is released from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What is the optimal length of a sarcomere responsible for?

    <p>Maximal tension generation.</p> Signup and view all the answers

    What is the primary function of Ca2+ ATPases in muscle contraction?

    <p>To actively pump Ca2+ back into the SR</p> Signup and view all the answers

    Which phase of a twitch contraction involves the formation of cross-bridges?

    <p>Contraction period</p> Signup and view all the answers

    What role does oxygen play in aerobic respiration for muscles?

    <p>Serves as the final electron acceptor</p> Signup and view all the answers

    What is the term for the process that occurs after an action potential passes and muscle relaxes?

    <p>Excitation-contraction coupling</p> Signup and view all the answers

    How does the frequency of action potentials affect muscle contraction?

    <p>More frequent action potentials lead to more tension</p> Signup and view all the answers

    What happens to acetylcholine at the neuromuscular junction after its release?

    <p>It is destroyed by an enzyme</p> Signup and view all the answers

    Which type of contraction involves the muscle shortening while generating constant tension?

    <p>Concentric contraction</p> Signup and view all the answers

    What is a motor unit composed of?

    <p>One somatic motor neuron and multiple muscle fibers</p> Signup and view all the answers

    Which process allows muscles to produce ATP rapidly during short bursts of activity?

    <p>Creatine phosphate utilization</p> Signup and view all the answers

    Muscle tone contributes to which of the following?

    <p>Preventing muscle fatigue</p> Signup and view all the answers

    What term describes the period when a muscle fiber cannot respond to a new action potential?

    <p>Refractory period</p> Signup and view all the answers

    What results from anaerobic glycolysis when oxygen is limited?

    <p>Formation of lactic acid</p> Signup and view all the answers

    What is the function of isotonic contractions?

    <p>To maintain a constant tension while changing length</p> Signup and view all the answers

    What happens during the latent period of a twitch contraction?

    <p>Action potential spreads through the sarcolemma</p> Signup and view all the answers

    Study Notes

    Introduction to Muscular Tissue

    • Three types of muscular tissue: skeletal, cardiac, and smooth
    • All muscles generate heat during contraction
    • Scientific study of muscular tissue is called myology.
    • Four special properties:
      • Electrically excitable: produce electrical signals called muscle action potentials, nerve tissues are also excitable.
      • Contractile: muscle action potentials stimulate contraction, contractions generate tension on bones for movement.
      • Extensible: tissue can be stretched without tearing, e.g., smooth muscle around the stomach.
      • Elastic: resting length is restored after stretching.

    Skeletal Muscle Structure

    • Cells of skeletal muscle tissue are called muscle fibers (myocytes)
    • Muscle fibers + connective tissue + nerve and blood supply = muscle (an organ)
    • Muscles are surrounded by fascia (connective tissue layers)
    • Fascia functions include grouping muscles with similar functions and providing passage for nerves and vasculature.
      • Epimysium: most superficial, dense irregular CT that wraps muscles
      • Perimysium: intermediate layer, dense irregular CT that wraps fascicles (bundles of muscle fibers)
      • Endomysium: deepest layer, mostly reticular fibers that wrap individual muscle fibers
    • Fascia forms tendons: connect muscles to bones
    • Aponeuroses: a special type of tendon that forms broad sheets, e.g., the occipitofrontalis muscle.
    • Muscular tissue requires access to oxygen-rich blood (extensively vascularized), this is used to make ATP.
    • Skeletal muscle fibers are extensively innervated by somatic motor neurons.
    • You are born with every muscle fiber you will ever have.
      • Start as immature cells called myoblasts in the womb.
      • Cells fuse as they mature --> large multinucleate cells.

    Myocyte Structure

    • The plasma membrane of myocytes is called the sarcolemma
      • Electrical signals run along this membrane.
      • Folds inwards or invaginates to form T-tubules.
    • The cytoplasm of myocytes is called the sarcoplasm
      • Densely packed with myofibrils.
      • Rich in glycogen (carbohydrate energy store).
    • Sarcoplasm contains myoglobin, which only found in muscle cells
      • Binds oxygen at an Fe-containing center called heme.
      • Allows myocytes to receive oxygen from inside and outside the cell.
    • The sarcoplasm is densely packed with myofibrils
      • Myofibrils are long threads of contractile protein filaments.
      • Regular pattern of overlapping filaments gives skeletal and cardiac muscle a striated appearance.

    Sarcoplasmic Reticulum

    • The SR is the specialized smooth endoplasmic reticulum in muscle cells
      • Extensively folded around each myofibril.
      • Membrane folds are called cisternae (singular: cistern).
      • Terminal cisternae specifically release Ca2+ to each T-tubule.
    • Where 2 terminal cisternae meet a T-tubule = a triad.
    • Muscular hypertrophy: an increase in sarcoplasmic volume
      • Each muscle fiber increases the volume of cellular contents, especially myofibrils.
      • Hypertrophy is a response to increased mechanical stress, hormones, and disease.

    Sarcomere Structure

    • Myofibrils are bundles of thread-like structures called myofilaments.
    • Each myofilament is made of contractile units called sarcomeres joined end-to-end.
    • Each sarcomere consists of overlapping thick and thin filaments
      • Thick filaments extend from the midline (M-line) of the sarcomere and are made of myosin.
      • Thin filaments extend from the ends (Z-discs) of the sarcomere and are made of actin.
    • The sarcomere is divided into zones and bands:
      • A band: regions where the thick and thin filaments overlap and everything in between.
      • H zone: regions between the zones of overlap around the M-line (only thick filaments).
      • I band: regions between zones of overlap around the Z-discs (only thin filaments).

    Muscle Contraction

    • Muscle contraction is driven by the shortening of the sarcomere as the thin filaments slide over the thick filaments.
    • This is called the sliding filament model.
      • Filaments do not change in length.
    • Myosin is a motor protein that converts chemical potential energy in ATP to mechanical energy.
    • Actin is a cytoskeletal protein that forms helical thin filaments with myosin-binding sites.
    • Three types of proteins involved in muscle contraction:
      • Contractile proteins: shorten the sarcomere
        • Myosin: motor protein, myosin “heads” extend from ends of thick filaments and contact thin filaments to pull them toward the M-line.
          • Each myosin head has an ATP-binding site and an actin-binding site.
        • Actin: cytoskeletal protein that forms helical thin filaments.
      • Regulatory proteins: control contraction
        • Troponin: binds Ca2+ and moves tropomyosin.
        • Tropomyosin: blocks myosin-binding sites on thin filaments.
      • Structural proteins: stabilize and/or connect the sarcomere and surrounding structures.
        • Titin: large elastic protein that spans the M-line to Z-discs.
        • Dystrophin: connects thin filaments to integral membrane proteins in the sarcolemma.

    Contraction Cycle

    • Myosin binds and hydrolyzes ATP
      • Energizes myosin and changes its conformation (cocked).
    • Myosin binds thin filaments to form a cross-bridge
    • Myosin pulls the thin filaments toward the M-line
      • This conformational change is called the power stroke.
    • Myosin releases the thin filaments
      • Requires binding of a new ATP molecule to myosin.
    • Troponin moves tropomyosin off the myosin-binding sites on actin when Ca2+ binds.
      • This allows myosin to form a cross-bridge.
    • Muscle contraction requires both ATP and Ca2+
    • As myosin pulls on the thin filaments, the Z-discs come together and the sarcomere shortens.
      • H zone disappears.
      • I band narrows.

    Length-Tension Relationship

    • There is an optimal sarcomere length for maximum tension generation.
      • Too much or too little overlap between thick and thin filaments reduces tension generated.
    • If the filaments completely overlap at rest, myosin cannot generate tension effectively.
    • If the filaments barely overlap at rest, myosin cannot generate much tension.

    Muscle Action Potentials

    • The intracellular Ca2+ concentration is kept exceedingly low.
      • Cells store Ca2+ in the SR.
      • Cells export Ca2+ using membrane transporters.
    • Somatic motor neurons release neurotransmitters (e.g., acetylcholine)
      • Bind protein receptors on muscle cells.
      • This leads to an action potential in the muscle cell.
    • The Na+-K+ pump maintains a negative resting membrane potential.
      • Moves 3 Na+ out of the cell and 2 K+ into the cell per ATP hydrolyzed.
    • Muscle action potentials:
      • During depolarization, the membrane potential rapidly becomes positive.
      • During repolarization, the membrane potential returns to resting potential.
    • Voltage-gated ion channels facilitate diffusion of ions down their concentration gradients.
      • VGNCs: allow Na+ ions to enter the cell.
      • VGKCs: allow K+ ions to exit the cell.
    • Acetylcholine binding opens some VGNCs, leading to slight depolarization.
    • VGNCs close as the membrane repolarizes.

    Excitation-Contraction Coupling

    • Action potentials travel along the sarcolemma to VGCCs at T-tubules.
      • VGCCs are physically connected to Ca2+ release channels in the SR membrane.
    • Action potentials open VGCCs, releasing Ca2+ from the SR.
      • Ca2+ binds troponin, moving tropomyosin off the myosin-binding sites on thin filaments.
    • During contraction:
      • Ca2+ release channels increase intracellular Ca2+ concentration 10X.
      • VGCCs in the sarcolemma close and the SR Ca2+ release channels close.
      • Ca2+-ATPases actively pump Ca2+ back into the SR and out of the cell.
      • This helps to relax the muscle.

    Control of Muscle Tension

    • Motor unit: 1 somatic motor neuron + all of the skeletal muscle fibres it synapses with.
    • Large muscles have motor units distributed throughout the muscles.
      • All muscle fibres in a motor unit contract and relax synchronously.
    • A twitch contraction is the contraction generated in all skeletal muscle fibres of one motor unit due to one action potential.
    • The refractory period is the time period when the muscle cannot respond to a new action potential simultaneously.
    • Motor unit recruitment: larger muscles distribute motor units to allow for a smooth, gradual increase in force.

    Muscle Tone

    • Muscle tone is the slight stiffness of muscles due to slight involuntary contractions of alternating motor units, helping to stabilize positions.
    • There are two types of muscle contraction:
      • Isotonic contractions: constant tension in the muscle as it changes length.
        • Concentric isotonic contractions: muscle shortens to decrease the angle around a joint, e.g., biceps brachii when picking up a book.
        • Eccentric isotonic contractions: muscle resists a load as it lengthens, e.g., biceps brachii when slowly putting a book down.
      • Isometric contractions: tension generated is not sufficient to overcome the resistance of the load, bones do not move, e.g., holding a book out to someone or holding a plank.

    Muscle Metabolism

    • Muscles need a lot of ATP:
      • For the contraction cycle.
      • For active transport pumps (e.g., Na+/K+ pump, Ca2+ pump).
    • Muscles generate ATP in three ways:
      • Consuming creatine phosphate: muscles rapidly dephosphorylate creatine phosphate and regenerate ATP
      • Aerobic respiration: glucose is broken down into pyruvate, pyruvate is transported to the mitochondrion and the electrons from the chemical bonds are transferred to the ETC, the flow of electrons down the ETC releases free energy that is harnessed to synthesize ATP, oxygen is the final electron acceptor in these reactions allowing for energy release.
      • Anaerobic glycolysis: if muscles have restricted access to oxygen (e.g., endurance or heavy resistance training), then they cannot respire the products of glycolysis and pyruvate will be fermented into lactic acid.

    Muscle Needs Oxygen After Exercise

    • Muscles have elevated oxygen consumption after exercise.
    • This is needed for:
      • Replenishing creatine phosphate stores.
      • Oxidizing lactic acid back to glucose.
      • Replenishing glycogen stores.

    Oxygen Debt

    • Muscles need oxygen during exercise to produce ATP.
    • After exercise, muscles need oxygen for several reasons:
      • Replenish myoglobin.
      • Convert lactic acid back to glucose in the liver.
      • Replenish creatine phosphate.
    • This post-exercise oxygen need is known as oxygen debt.

    Muscle Fiber Types

    • There are three types of skeletal muscle fibers:
      • Slow Oxidative Fibers:
        • Dark red due to high myoglobin and capillary content.
        • "Slow" refers to their relatively long contraction cycle (100-200 milliseconds).
        • Also called slow twitch fibers.
        • Resist fatigue, making them suitable for endurance activities and postural muscles.
        • "Oxidative" means they mainly rely on aerobic respiration for energy.
      • Fast Oxidative-Glycolytic Fibers:
        • Dark red and the largest fibers, with high myoglobin and capillary content.
        • "Fast" refers to their shorter contraction cycle.
        • They can use both aerobic and anaerobic respiration for energy.
      • Fast Glycolytic Fibers:
        • White due to low myoglobin content.
        • "Fast" refers to their shortest contraction cycle.
        • They primarily use anaerobic glycolysis for energy, making them prone to fatigue.
        • These fibers are well-suited for short bursts of high-intensity activity.

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    Description

    This quiz covers the fundamentals of muscular tissue, including its three types: skeletal, cardiac, and smooth. You will explore the properties of muscles, such as contractility, extensibility, and elasticity, as well as the structure of skeletal muscle. Test your knowledge of myology and the functional roles of muscular tissue.

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