Muscle Tissue Quiz
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Questions and Answers

What is the primary function of cardiac muscle tissue?

  • To stabilize body positions
  • To move skeletal bones
  • To regulate passage of substances
  • To move blood through the heart (correct)

    • Skeletal muscle tissue is responsible for regulating the passage of substances through the body.

    False

    What is the scientific study of muscular tissue called?

    myology

    Muscular tissue is _____, meaning it can be stretched without tearing.

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

    Which type of muscular tissue generates tension to move bones?

    <p>Skeletal muscle</p> Signup and view all the answers

    Match each layer of fascia with its description:

    <p>Epimysium = Most superficial layer, wraps whole muscles Perimysium = Wraps bundles of muscle fibers (fascicles) Endomysium = Surrounds individual muscle fibers</p> Signup and view all the answers

    What are myocytes more commonly known as?

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

    Muscular tissue is neither elastic nor capable of generating heat during contraction.

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

    What is the final electron acceptor in aerobic respiration?

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

    Lactic acid fermentation occurs when oxygen is abundant.

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

    What is the primary role of pyruvate in aerobic respiration?

    <p>Transported to the mitochondrion for further reactions.</p> Signup and view all the answers

    Muscles need oxygen after exercise to replenish _____________.

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

    What is the main metabolic mode of slow oxidative fibers?

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

    The process of splitting glucose is called _____________.

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

    Match the type of muscle fiber with its description:

    <p>Slow oxidative fibres = Do not fatigue easily, used in endurance activities Fast oxidative-glycolytic fibres = Large fibers, can perform both aerobic and anaerobic metabolism Fast glycolytic fibres = Fatigue quickly, primarily anaerobic metabolism</p> Signup and view all the answers

    Fast glycolytic fibers are primarily used for endurance activities.

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

    What type of fibers mostly make up the endomysium?

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

    Aponeuroses are a type of tendon that forms broad sheets.

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

    What do muscles connect to?

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

    Each muscle fibre is regulated by ________ motor neurons.

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

    Which component in muscle cells binds oxygen?

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

    Muscle fibers can divide to increase muscle mass.

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

    The plasma membrane of myocytes is called the ________.

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

    Match the following components with their functions:

    <p>Myosin = Motor protein Actin = Forms thin filaments Troponin = Binds Ca2+ Titin = Stabilizes thick filaments</p> Signup and view all the answers

    What is the specialized smooth endoplasmic reticulum in muscle cells called?

    <p>sarcoplasmic reticulum</p> Signup and view all the answers

    What is the primary role of regulatory proteins in muscle contraction?

    <p>To control contraction</p> Signup and view all the answers

    Dystrophin reinforces sarcomere structure and transmits tension to tendons.

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

    Muscular hypertrophy is an increase in ________ volume.

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

    What are contractile proteins responsible for?

    <p>Shortening the sarcomere</p> Signup and view all the answers

    What do thick filaments in a sarcomere consist of?

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

    The light bands in a sarcomere are referred to as the ________ band.

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

    What is the primary role of dystrophin in muscle cells?

    <p>Links actin filaments to the dystrophin-glycoprotein complex</p> Signup and view all the answers

    The sliding filament model states that the thick and thin filaments change in length during muscle contraction.

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

    What molecule must bind to myosin for it to release thin filaments?

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

    Dystrophin helps maintain the ___________ and integrity of muscle fibers during contraction.

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

    Match the following ion channels with their function:

    <p>Voltage-gated sodium channels = Facilitate depolarization by allowing Na+ ions in Calcium channels = Release Ca2+ for muscle contraction Potassium channels = Help repolarize the membrane Sodium-potassium pump = Maintain resting membrane potential</p> Signup and view all the answers

    Which part of the sarcomere disappears during contraction?

    <p>H zone</p> Signup and view all the answers

    Muscle contraction requires both ATP and Ca2+.

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

    What happens to the membrane potential of a muscle cell during an action potential?

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

    The ___________ phase of the contraction cycle involves myosin binding and hydrolyzing ATP.

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

    How does muscle fiber transmit tension to the bone?

    <p>By shortening adjacent sarcomeres</p> Signup and view all the answers

    Troponin and tropomyosin regulate the contraction of muscle fibers.

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

    Where is calcium stored in muscle cells?

    <p>Sarcoplasmic reticulum</p> Signup and view all the answers

    The ___________ of a muscle action potential involves the restoration of a negative membrane potential after depolarization.

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

    Match the muscle contraction components with their functions:

    <p>Myosin = Binds thin filaments Actin = Forms cross-bridges with myosin Tropomyosin = Covers myosin-binding sites Troponin = Binds Ca2+ to regulate contraction</p> Signup and view all the answers

    What is the role of voltage-gated K+ channels (VGKCs) during the repolarization phase?

    <p>To allow K+ to flow out of cells</p> Signup and view all the answers

    Voltage-gated Ca2+ channels (VGCCs) are located on the sarcoplasmic reticulum (SR).

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

    What happens to acetylcholine at the neuromuscular junction?

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

    During muscle contraction, Ca2+ is released from the _________.

    <p>sarcoplasmic reticulum</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Creatine Phosphate = Used to rapidly regenerate ATP Isotonic Contraction = Muscle changes length as it generates constant tension Refractory Period = Time during which a muscle cannot respond to a new action potential Motor Unit = A somatic motor neuron and all muscle fibers it innervates</p> Signup and view all the answers

    What is the primary purpose of muscle tone?

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

    All muscle fibers in a motor unit contract simultaneously.

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

    What is a twitch contraction?

    <p>A contraction generated in all skeletal muscle fibers of one motor unit due to one action potential.</p> Signup and view all the answers

    The _________ phase occurs after the action potential has passed and involves pumping Ca2+ back into the SR.

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

    Which contraction occurs when a muscle shortens while generating force?

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

    A motor unit consists only of one skeletal muscle fiber.

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

    What is the function of creatine kinase in muscle metabolism?

    <p>It catalyzes the transfer of phosphate to regenerate ATP from creatine phosphate.</p> Signup and view all the answers

    The ________ period is the time it takes for a muscle fiber to recover and become responsive to a new action potential.

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

    Match the following muscle contraction types with their characteristics:

    <p>Isometric Contraction = Tension generated is not sufficient to move a load Concentric Contraction = Muscle shortens while lifting a load Eccentric Contraction = Muscle lengthens while resisting a load Twitch Contraction = Temporary contraction from a single action potential</p> Signup and view all the answers

    Study Notes

    Introduction to Muscular Tissue

    • There are three types of muscular tissue: skeletal, cardiac, and smooth.
    • All muscle tissue generates heat during contraction.
    • Muscular tissue is electrically excitable, contractile, extensible, and elastic.
    • Skeletal muscle tissue contracts to move bones and stabilize body positions.
    • Cardiac muscle tissue contracts to move blood through the heart.
    • Smooth muscle tissue contracts to regulate the passage of substances through the body, for example, the gastrointestinal tract and blood vessels.
    • The scientific study of muscular tissue is called myology.
    • Nerve tissue is also electrically excitable.
    • Contractions generate tension on bones, which leads to movement.
    • Muscle tissue can be stretched without tearing, for example, smooth muscle around the stomach.
    • Muscle tissue returns to its resting length after stretching.

    Structure of Skeletal Muscle

    • The cells of skeletal muscle tissue are called muscle fibers.
    • Muscle fibers are elongated cells also known as myocytes.
    • Muscle fibers contain bunched protein filaments called myofibrils.
    • Muscle fibers + connective tissue + nerve and blood supply = muscle (an organ).
    • Muscles are surrounded by connective tissue layers called fascia.
    • Fascia physically groups muscles with similar functions together and provides passage for nerves and vasculature.
    • Fascia are composed of three layers: epimysium, perimysium, and endomysium.
    • Epimysium is the most superficial layer of fascia, wrapping the entire muscle. It is dense irregular connective tissue.
    • Perimysium is the intermediate layer of fascia, wrapping fascicles (bundles of muscle fibers). It is also dense irregular connective tissue.
    • Endomysium is the deepest layer of fascia wrapping individual muscle fibers. It is composed mostly of reticular fibers.
    • Fascia form tendons, which connect muscles to bones.
    • Aponeuroses are a special type of tendon that forms broad sheets, for example, the two bellies of the occipitofrontalis muscle are connected by the epicranial aponeurosis.
    • Muscular tissue requires oxygen-rich blood.
    • Muscular tissue is extensively vascularized because it uses a lot of oxygen to make ATP.
    • Skeletal muscles are also extensively innervated.
    • Voluntary muscle contraction is regulated by somatic motor neurons.
    • Axons from the spinal cord branch to muscles, typically one branch per muscle fiber.

    Skeletal Muscle Fiber Structure

    • You are born with all the muscle fibers you will ever have.
    • Muscle fibers begin as immature cells, called myoblasts, in the womb.
    • Myoblasts fuse as they mature to form large multinucleate cells.
    • The plasma membrane of myocytes is called the sarcolemma.
    • Electrical signals run along the sarcolemma.
    • The sarcolemma folds inwards or invaginates to form T-tubules.
    • The cytoplasm of myocytes is called the sarcoplasm.
    • The sarcoplasm is densely packed with myofibrils.
    • The sarcoplasm is rich in glycogen (carbohydrate energy store).
    • The sarcoplasm also contains myoglobin.
    • Myoglobin is only found in muscle cells.
    • Myoglobin binds oxygen at an Fe-containing center called heme.
    • Myocytes receive oxygen from inside and outside the cell.
    • Myofibrils are long threads of contractile protein filaments (~2 nm diameter).
    • The regular pattern of overlapping filaments gives skeletal and cardiac muscle a striated appearance.

    The Sarcoplasmic Reticulum

    • The sarcoplasmic reticulum (SR) is the specialized smooth endoplasmic reticulum in muscle cells.
    • The SR is extensively folded around each myofibril.
    • Membrane folds of the SR are called cisternae.
    • The terminal cisternae specifically release Ca2+ to each T-tubule.
    • Where two terminal cisternae meet a T-tubule, it forms a triad.
    • Muscle fibers do not divide, but they can grow by laying down new protein and enlarging (hypertrophy).

    Muscular Hypertrophy

    • Muscular hypertrophy is an increase in sarcoplasmic volume.
    • Each muscle fiber increases the volume of cellular contents, especially myofibrils.
    • Hypertrophy is a response to increased mechanical stress (e.g., weight-bearing exercise), hormones (e.g., anabolic steroids), and disease (e.g., increased demand on a diseased heart).

    Sarcomere Structure

    • Myofibrils are bundles of thread-like structures called myofilaments.
    • Each myofilament is made up 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, H zone, and I band.
    • The A band is where the thick and thin filaments overlap.
    • The H zone is the region between zones of overlap around the M-line, containing only thick filaments.
    • The I band is the region between zones of overlap around the Z-discs, containing only thin filaments.

    Muscle Contraction

    • Muscles generate force by contraction.
    • There are three types of proteins involved in muscle contraction: contractile, regulatory, and structural proteins.
    • Myosin is a motor protein that converts chemical potential energy in ATP to mechanical energy.
    • Each thick filament consists of ~300 myosin proteins.
    • Myosin “heads” extend radially from the 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 is a cytoskeletal protein that forms long twisted threads that make up thin filaments.
    • Actin has myosin-binding sites.
    • Regulatory proteins associate with thick and thin filaments to 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 is a large elastic protein spanning the M-line to Z-discs, stabilizing the position of thick filaments.
    • Dystrophin connects thin filaments to integral membrane proteins in the sarcolemma and reinforces sarcomere structure.
    • Dystrophin transmits tension of sarcomeres to tendons.

    Muscle Contraction by the Sliding Filament Model

    • The sarcomere shortens as the thin filaments slide over the thick filaments.
    • This mechanism is called the sliding filament model.
    • Filaments do not change in length during muscle contraction.

    The Contraction Cycle

    • Myosin binds to the thin filaments, pulls them towards the M-line, and then releases them.
    • This iterative binding and release is called the contraction cycle.
    • Myosin binds and hydrolyzes ATP to energize itself and change its conformation.
    • Myosin binds to 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 after binding a new ATP molecule.
    • The myosin-binding sites on the thin filaments are obscured by tropomyosin.
    • Troponin binds Ca2+ and moves tropomyosin off the myosin-binding sites on actin, allowing 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, the sarcomere shortens, the H zone disappears, and the I band narrows.

    How Do Sarcomeres Move Bones?

    • When sarcomeres shorten, they pull on adjacent sarcomeres, ultimately resulting in the shortening of the entire muscle fiber.

    The Length-Tension Relationship

    • The amount of filament overlap impacts muscle tension.
    • If the thick and thin filaments completely overlap at rest, myosin cannot generate tension effectively.
    • If the thick and thin filaments barely overlap at rest, myosin cannot generate much tension.
    • There is an optimal sarcomere length that provides sufficient filament overlap to generate maximal tension.

    Muscle Action Potentials

    • The intracellular Ca2+ concentration is kept low in most cells.
    • Cells store Ca2+ in the sarcoplasmic reticulum.
    • Cells export Ca2+ using membrane transporters.
    • Muscle fibers are electrically excitable.
    • Signals from somatic motor neurons stimulate an action potential.
    • Somatic motor neurons release neurotransmitters (e.g., acetylcholine), which bind to protein receptors on muscle cells and lead to action potential in muscle cells.
    • Na+-K+ pump keeps the inside of animal cells negative compared to the outside.
    • The pump moves 3 Na+ out of the cell and 2 K+ into the cell per ATP hydrolyzed.
    • All cells maintain a negative resting membrane potential.

    The Muscle Action Potential

    • During an action potential, the membrane potential rapidly becomes positive. This is called depolarization.
    • The cell needs to return to resting potential after depolarization, which is called repolarization.
    • Changes in membrane potential during action potentials are caused by plasma membrane transporters, specifically voltage-gated ion channels.
    • Voltage-gated ion channels open in response to a change in membrane potential.
    • Voltage-gated sodium (Na+) channels (VGNCs) allow Na+ ions to enter the cell.
    • VGNCs open only when a change in membrane potential occurs.
    • Acetylcholine binding opens some Na+ channels, causing slight depolarization.
    • This depolarization influx of positive Na ions causes the membrane potential to become more positive.
    • Repolarization is caused by voltage-gated potassium (K+) channels (VGKCs).
    • VGKCs open slower in response to membrane potential changes.
    • Once VGKCs open, K+ flows out of cells, restoring resting membrane potential.
    • VGNCs close as the membrane repolarizes.

    Excitation-Contraction Coupling

    • The action potential travels along the sarcolemma to voltage-gated Ca2+ channels (VGCCs) at T-tubules.
    • VGCCs are physically connected to the sarcolemma because they plug Ca2+ release channels in the SR membrane.
    • Action potentials open VGCCs at triads, which releases and opens Ca2+ release channels of the SR.
    • Ca2+ spills into the sarcoplasm and binds troponin.
    • Troponin moves tropomyosin off the myosin-binding sites on thin filaments, initiating muscle contraction.

    During Contraction

    • The Ca2+ release channels increase the intracellular Ca2+ concentration by ~10X.
    • When the muscle action potential has passed, VGCCs in the sarcolemma close, and SR Ca2+ release channels close and reassociate with the VGCCs at triads.
    • Ca2+-ATPases actively pump Ca2+ back into the SR and out of the cell.
    • This process is called excitation-contraction coupling.

    What Happens to Acetylcholine at the NMJ?

    • Acetylcholine is broken down and destroyed by the enzyme acetylcholinesterase.

    Control of Muscle Tension

    • One action potential typically equals one contraction.
    • More frequent action potentials result in more tension.
    • Each somatic motor neuron axon can form multiple NMJs with muscle fibers.
    • A motor unit is one somatic motor neuron plus all the skeletal muscle fibers it synapses with.
    • Large muscles have many motor units distributed throughout the muscle.
    • All muscle fibers in a motor unit contract and relax synchronously.

    Muscle Twitch

    • A twitch contraction is the contraction generated in all skeletal muscle fibers of one motor unit due to one action potential.
    • Twitch contractions proceed in three phases: latent period, contraction period, and relaxation period.
    • Latent period (2 msec) is the delay between the stimulus and muscle action.
    • Contraction period (10–100 msec) is when cross-bridges form and sarcomeres shorten.
    • Relaxation period (10–100 msec) is when Ca2+ is pumped back into the SR, myosin detaches from actin, and tension decreases.

    Refractory Period

    • If a muscle fiber is responding to an action potential, it cannot respond simultaneously to a new action potential.
    • This temporary unresponsiveness is called a refractory period.

    Muscle Tone

    • Some skeletal muscles produce enough tension to stabilize positions but not enough to move bones.
    • This prevents muscle fatigue and helps to make movements smooth.
    • For large muscles, weak motor units work first, and stronger motor units work second.
    • This process is called motor unit recruitment.
    • Muscle tone is the slight involuntary contractions of alternating motor units, resulting in a slight stiffness of the muscle.

    Types of Muscle Contractions:

    • Isotonic contractions: constant tension in the muscle as it changes length.
    • Concentric isotonic contractions: the muscle shortens to decrease the angle around a joint. (e.g., biceps brachii contract to pick up a book).
    • Eccentric isotonic contractions: the muscle resists a load as it lengthens. (e.g., biceps brachii lengthens as you slowly put a book down).
    • Isometric contractions: tension generated is not sufficient to overcome the resistance of the load, and bones do not move. (e.g., holding a book out or holding a plank).
    • Isometric contractions stabilize joints during movement.

    Muscle Metabolism

    • Muscles need ATP to power the contraction cycle and active-transport Ca++ pumps in the SR.
    • Muscles generate ATP in three ways: consuming creatine phosphate, anaerobic glycolysis, and aerobic respiration.
    • Creatine is a small molecule made in the liver, kidneys, and pancreas.
    • At rest, unused ATP is dephosphorylated to make creatine phosphate.
    • At work, muscles rapidly dephosphorylate creatine phosphate to regenerate ATP.
    • Both phosphate transfers are catalyzed by creatine kinase.
    • Anaerobic glycolysis is the breakdown of glucose to pyruvate without oxygen.
    • This produces ATP rapidly but only for a short time, resulting in lactic acid build-up.
    • Aerobic respiration uses oxygen to break down glucose, creating much more ATP than anaerobic glycolysis.
    • This is a longer-lasting process than anaerobic glycolysis.

    Aerobic Respiration

    • Muscles can release stored glucose from glycogen or take up glucose from the blood
    • In 10 chemical reactions glucose is broken down into two 3-carbon molecules called pyruvate
    • This process of splitting glucose is called glycolysis
    • If sufficient oxygen is present, then pyruvate is transported to the mitochondria
    • In the mitochondria, many reactions convert the carbons in glucose to CO2 which is exhaled
    • Electrons are transferred to the electron transport chain (ETC)
    • The flow of electrons down the ETC releases free energy that is used to synthesize ATP
    • Oxygen is the final electron acceptor of the ETC and allows for the release of energy

    Anaerobic Glycolysis

    • If muscles have restricted access to oxygen, they cannot respire the products of glycolysis
    • Pyruvate will be fermented into lactic acid
    • Lactic acid fermentation regenerates NAD+ in the process, allowing glycolysis to continue making ATP in low-oxygen conditions

    Oxygen Debt

    • Muscles need oxygen after exercise to:
      • Replenish myoglobin
      • Convert lactic acid back to glucose in the liver
      • Replenish creatine phosphate

    Types of Muscle Fibers

    • There are three types of skeletal muscle fibers with different structures, functions, and appearances:
      • Slow oxidative fibers
      • Fast oxidative-glycolytic fibers
      • Fast glycolytic fibers

    Slow Oxidative Fibers

    • Dark red in color due to lots of myoglobin and capillaries
    • Called "slow twitch" because they have a long contraction cycle (100-200 msec)
    • Do not fatigue easily, therefore they function during endurance activities and in postural muscles
    • "Oxidative" refers to aerobic respiration as their main metabolic mode

    Fast Oxidative-Glycolytic Fibers

    • Dark red in color due to lots of myoglobin and capillaries
    • They are the largest fibers
    • "Fast" refers to their short contraction cycle (50 msec)
    • They are a mix of aerobic and anaerobic respiration, therefore they are involved in prolonged activities such as running
    • They resist fatigue better than fast glycolytic fibers

    Fast Glycolytic Fibers

    • White in color due to low myoglobin and capillaries
    • "Fast" refers to their short contraction cycle (50 msec)
    • "Glycolytic" refers to their use anaerobic glycolysis
    • Fatigue quickly and contract powerfully but are primarily used for short bursts activities such as sprinting and weight lifting

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    Test your knowledge on the various types of muscular tissue, their functions, and metabolic processes. This quiz covers topics such as cardiac, skeletal, and smooth muscle, as well as concepts of aerobic respiration and muscle fibers. Perfect for anatomy and physiology enthusiasts!

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