Muscular System Function and Properties
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Muscular System Function and Properties

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Questions and Answers

Which type of muscle is voluntary?

  • Both A and C
  • Skeletal muscle (correct)
  • Cardiac muscle
  • Smooth muscle

    • What is the basic structural and functional unit of a skeletal muscle?

  • Myofibril
  • Sarcoplasm
  • Sarcomere (correct)
  • Cell

    • Which of the following is not a function of the muscular system?

  • Excretion (correct)
  • Communication
  • Respiration
  • Movement

    • Which muscle type is classified as voluntary?

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

    Which of the following definitions correctly describes extensibility?

    <p>Ability of a muscle to be stretched beyond its normal resting length and still contract</p> Signup and view all the answers

    What is the basic functional unit of skeletal muscle?

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

    Which of the following is NOT a function of the muscular system?

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

    Which structure of the muscle fiber helps with the regulation of intracellular calcium levels?

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

    What does the term 'extensibility' refer to in muscle physiology?

    <p>Ability to be stretched beyond normal resting length and still contract</p> Signup and view all the answers

    Which component of muscles is responsible for facilitating communication between muscle fibers?

    <p>T Tubule</p> Signup and view all the answers

    What characteristic primarily distinguishes skeletal muscle from other muscle types?

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

    Which structure in muscle fibers is primarily responsible for the regulation of intracellular calcium levels?

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

    Which function does NOT pertain to skeletal muscles?

    <p>Contraction of heart</p> Signup and view all the answers

    Which muscle property allows it to respond to stimuli and generate force?

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

    Which of the following definitions describes the ability of muscle to return to its original length after being stretched?

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

    Among the following, which is a major function of the muscular system linked to communication?

    <p>Facial expressions</p> Signup and view all the answers

    In which way does skeletal muscle contribute to maintaining body temperature?

    <p>By contracting and generating heat</p> Signup and view all the answers

    Which type of muscle is not under voluntary control?

    <p>Both B and C</p> Signup and view all the answers

    What role do skeletal muscles play in respiration?

    <p>They contract and relax to facilitate breathing</p> Signup and view all the answers

    What is the relationship between skeletal muscles and posture maintenance?

    <p>They enable active maintenance of posture through contractions</p> Signup and view all the answers

    What primary function do skeletal muscles perform to help maintain posture?

    <p>They contract to maintain muscle tone.</p> Signup and view all the answers

    How do skeletal muscles contribute to respiration?

    <p>By contracting the diaphragm and thoracic muscles.</p> Signup and view all the answers

    Which function of muscles involves the creation of heat as a by-product?

    <p>Production of body heat.</p> Signup and view all the answers

    Which type of muscle is responsible for the contraction of the heart?

    <p>Cardiac muscle.</p> Signup and view all the answers

    What is contractility defined as in muscle tissue?

    <p>Ability to shorten forcefully.</p> Signup and view all the answers

    Which property of muscle allows it to return to its original shape after being stretched?

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

    What role do smooth muscles play in the body?

    <p>Constricting blood vessels and organs.</p> Signup and view all the answers

    Which function of the muscular system is involved in all aspects of human interaction?

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

    What occurs during muscle extensibility?

    <p>Muscle can be stretched.</p> Signup and view all the answers

    In terms of muscle function, which of the following is a primary role of skeletal muscle?

    <p>It allows for body movement.</p> Signup and view all the answers

    What is the term for the muscle's ability to return to its original length after being stretched?

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

    Which connective tissue surrounds a bundle of muscle fibers known as a fascicle?

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

    What structure in a muscle cell is responsible for storing calcium ions?

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

    Which protein subunit is a key component of thin myofilaments?

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

    What describes the structure that extends from one Z line to another in a muscle fiber?

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

    Which muscle tissue type is primarily under voluntary control?

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

    What is the name of the covering that surrounds the entire muscle?

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

    Which term refers to the capacity of a muscle to be stimulated and contract?

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

    What term is used for the structure that connects muscle to bone?

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

    In a sarcomere, which proteins are primarily responsible for contraction?

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

    What is the primary role of the presynaptic terminal in muscle contraction?

    <p>To release neurotransmitters for muscle stimulation</p> Signup and view all the answers

    What connects the neuronal axon to the muscle fiber at the neuromuscular junction?

    <p>Motor end plate</p> Signup and view all the answers

    Which ion's influx is critical for initiating the release of acetylcholine at the neuromuscular junction?

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

    What is the name of the gap that separates the axonal ending and the muscle fiber?

    <p>Synaptic cleft</p> Signup and view all the answers

    Which component in the axonal endings contains the neurotransmitter crucial for muscle activation?

    <p>Synaptic vesicles</p> Signup and view all the answers

    What primarily occurs at the neuromuscular junction to initiate muscle contraction?

    <p>Activation of voltage-gated calcium channels</p> Signup and view all the answers

    What role does acetylcholine play at the neuromuscular junction?

    <p>It binds to receptors on the muscle plasma membrane</p> Signup and view all the answers

    In muscle physiology, what is a primary consequence of the action potential arriving at the presynaptic terminal?

    <p>Calcium channels open and neurotransmission occurs</p> Signup and view all the answers

    Which statement accurately describes the role of tropomyosin in muscle contraction?

    <p>Tropomyosin has a binding site for calcium.</p> Signup and view all the answers

    What is the primary function of the T tubule in skeletal muscle fibers?

    <p>To invaginate the sarcolemma into the muscle fiber.</p> Signup and view all the answers

    During a heavy weight lifting attempt where the weight is immovable, what type of contraction is primarily occurring?

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

    Which sequence correctly depicts the events leading to muscle contraction?

    <p>2, 3, 7</p> Signup and view all the answers

    What component of muscle contraction directly binds to an active site on G actin?

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

    What is the primary role of troponin in muscle contraction?

    <p>To bind calcium and prevent tropomyosin from uncovering active sites</p> Signup and view all the answers

    Which event is necessary for the initiation of muscle contraction?

    <p>Release of acetylcholine at the motor end plate</p> Signup and view all the answers

    At what age does the loss of muscle fibers begin?

    <p>25 years old</p> Signup and view all the answers

    Which mechanism is NOT involved in muscle fatigue?

    <p>Hemoglobin saturation</p> Signup and view all the answers

    During muscle relaxation, what happens to calcium in the muscle fiber?

    <p>Calcium diffuses away from troponin molecules</p> Signup and view all the answers

    What is the primary cause of muscle soreness after vigorous exercise?

    <p>Inflammatory chemical influx</p> Signup and view all the answers

    What distinguishes isometric contractions from isotonic contractions?

    <p>Muscle tension increases without shortening</p> Signup and view all the answers

    The hinge region of myosin molecules allows which function?

    <p>Formation of cross bridges with actin</p> Signup and view all the answers

    What condition is marked by painful spastic contractions of skeletal muscle?

    <p>Muscle cramps</p> Signup and view all the answers

    What initiates the release of acetylcholine from synaptic vesicles?

    <p>Calcium influx into the presynaptic terminal</p> Signup and view all the answers

    What primarily triggers contraction in skeletal muscle cells?

    <p>A rise in intracellular calcium levels</p> Signup and view all the answers

    Which of the following statements about Myasthenia Gravis is true?

    <p>It involves production of autoantibodies against acetylcholine receptors.</p> Signup and view all the answers

    What is the main character of Duchenne Muscular Dystrophy?

    <p>It involves mutations in the dystrophin gene.</p> Signup and view all the answers

    What occurs immediately after acetylcholine binds to ligand-gated sodium channels on the motor end plate?

    <p>Sodium enters the muscle fiber</p> Signup and view all the answers

    What happens during the cessation of action potential along the sarcolemma?

    <p>Cross bridge formation is halted</p> Signup and view all the answers

    Which diagnostic test is appropriate for identifying Duchenne Muscular Dystrophy?

    <p>Serum creatinine levels</p> Signup and view all the answers

    What is the function of acetylcholinesterase in the synaptic cleft?

    <p>To remove acetylcholine</p> Signup and view all the answers

    What defines an eccentric contraction?

    <p>Muscle lengthens while maintaining tension</p> Signup and view all the answers

    What role do the troponin complexes play in muscle contraction?

    <p>Regulating binding sites on actin</p> Signup and view all the answers

    What role does tropomyosin play in muscle contraction?

    <p>It covers active sites on G actin</p> Signup and view all the answers

    What causes tendinitis in skeletal muscles?

    <p>Overuse of skeletal muscle</p> Signup and view all the answers

    What is fibromyalgia primarily characterized by?

    <p>Chronic widespread pain in skeletal muscles</p> Signup and view all the answers

    How is choline recycled to the presynaptic terminal?

    <p>Symported with sodium</p> Signup and view all the answers

    What is a consequence of calcium returning to the sarcoplasmic reticulum?

    <p>Tropomyosin returns to cover active sites on actin</p> Signup and view all the answers

    Which component of the muscle contraction process ensures that ligand-gated sodium channels close?

    <p>Acetylcholine unbinding</p> Signup and view all the answers

    What triggers the generation of an action potential in a muscle fiber?

    <p>Threshold depolarization due to sodium influx</p> Signup and view all the answers

    What is the primary structure that forms the fibrous actin in muscle fibers?

    <p>Globular (G) actin</p> Signup and view all the answers

    What ensures the tropomyosin does not uncover active sites on actin in a relaxed muscle?

    <p>Troponin anchoring tropomyosin</p> Signup and view all the answers

    What happens to acetylcholine after it has fulfilled its role in muscle contraction?

    <p>It is degraded by enzymes</p> Signup and view all the answers

    Study Notes

    Muscular System Function

    • Movement of the Body: Skeletal muscles attached to bones are responsible for movement.
    • Maintenance of Posture: Skeletal muscles maintain tone to keep the body upright.
    • Respiration: Skeletal muscles in the thorax and diaphragm contract for breathing.
    • Production of Body Heat: Skeletal muscle contraction produces heat as a byproduct.
    • Communication: Facial muscles and vocal cords enable communication.
    • Constriction of Organs and Vessels: Smooth muscle contraction in internal organs and vessels aids in constriction.
    • Contraction of the Heart: Cardiac muscle contraction pumps blood throughout the body.

    Functional Properties of Muscle Tissue

    • Contractility: Muscle tissue's ability to shorten forcefully.
    • Excitability: Muscle tissue can be stimulated to contract by a nerve.
    • Extensibility: Muscle tissue's ability to stretch beyond its normal resting length and still contract.
    • Elasticity: Muscle tissue has the ability to return to its original resting length after being stretched.

    Neuromuscular Junction

    • The neuromuscular junction is where a nerve stimulates a muscle cell.
    • It is formed by the axonal endings and the motor end plate.

    Axonal Endings

    • Contain small membranous sacs called synaptic vesicles.
    • These vesicles contain acetylcholine.

    Motor End Plate

    • The muscle plasma membrane in the area of the junction.
    • Contains acetylcholine receptors.

    Synaptic Cleft

    • The space between the axonal endings and muscle fibers.

    Muscle Contraction

    • Muscle contraction happens at the neuromuscular junction.
    • Steps involved:
      • Action potential arrives at the presynaptic terminal, opening voltage-gated calcium channels.
      • Calcium triggers the release of acetylcholine from synaptic vesicles by exocytosis.
      • Acetylcholine diffuses across the synaptic cleft and binds to ligand-gated sodium channels on the motor end plate.
      • Sodium enters the muscle fiber, causing depolarization, which can generate an action potential.
      • Acetylcholine detaches from the channels, which close.
      • Acetylcholinesterase removes acetylcholine from the synaptic cleft.
      • Choline is transported back into the presynaptic terminal with sodium.
      • Acetylcholine is reformed within the presynaptic terminal.

    Actin Myofilament Structure

    • Composed of:
      • Globular (G) actin: Globular subunits that form fibrous (F) actin.
      • Tropomyosin: Covers the active sites on G actin subunits in relaxed muscle.
      • Troponin: Anchors to actin, prevents tropomyosin from uncovering active sites, and binds calcium.

    Myosin Myofilament Structure

    • Composed of myosin molecules:
      • Two myosin heavy chains.
      • Two myosin heads: Bind to active sites on actin to form cross-bridges, attached to the rod portion by a hinge region, and contain ATPase enzymes.

    Excitation-Contraction Coupling

    • The link between the electrical component of muscle contraction and the mechanical component.
    • Occurs at the triad, where a T tubule and two terminal cisternae of the sarcoplasmic reticulum come together.
    • For a skeletal muscle to contract, it must:
      • Be stimulated by a nerve ending.
      • Have an action potential propagated along its sarcolemma.
      • Have an increase in intracellular calcium levels.

    Cross-Bridge Movement

    • The myosin head binds to an active site on actin to form a cross-bridge.
    • The myosin head pivots, pulling the actin filament towards the center of the sarcomere.
    • This movement is powered by ATP hydrolysis.
    • The cross-bridge detaches, and the cycle repeats as long as calcium is present.

    Muscle Relaxation

    • Occurs when:
      • Acetylcholine is no longer released at the neuromuscular junction.
      • The action potential along the sarcolemma stops, halting calcium release.
      • Calcium diffuses away from troponin molecules.
      • Tropomyosin covers the active sites on G actin.
      • Cross-bridge formation ceases.

    Types of Muscle Contractions

    • Isometric: Muscle does not shorten, tension increases.
    • Isotonic: Muscle shortens, tone remains constant throughout the contraction.
      • Concentric: Muscle shortens as it contracts.
      • Eccentric: Muscle lengthens as it contracts.

    Diseases of the Muscular System

    • Aging:

      • Muscle atrophy: Age-related reduction in muscle mass and function.
      • Loss of muscle fibers starts around 25 years old.
      • Surface area of the NMJ and number of motor neurons decreases.

    • Muscle Fatigue:

      • Temporary state of reduced work capacity.
      • Mechanisms involved: Acidosis, ATP depletion, oxidative stress, and local inflammatory response.

    • Muscle Soreness:

      • Occurs after vigorous exercise.
      • Caused by inflammatory chemicals in the muscle fibers.

    • Cramps:

      • Painful, spastic contractions of skeletal muscle.
      • Causes: Dehydration and ion imbalance.

    • Tendonitis:

      • Inflammation of a tendon or its attachment point due to overuse.

    • Fibromyalgia:

      • Chronic, widespread pain in skeletal muscles with no known cure.
      • Chronic muscle pain syndrome.

    • Myasthenia Gravis:

      • Autoimmune disease.
      • Production of autoantibodies that bind to acetylcholine receptors.
      • Diagnostics: Electromyography and identification of autoantibodies.

    • Duchenne Muscular Dystrophy:

      • Mutations in the dystrophin gene on the X chromosome.
      • Progressive muscle weakness and muscle contractures.
      • Slow motor development with progressive weakness and muscle wasting.
      • Diagnostics: Serum creatinine, muscle biopsies, and immunohistochemical studies.

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    Description

    This quiz covers the various functions of the muscular system, including movement, posture maintenance, respiration, and heat production. It also highlights the functional properties of muscle tissue such as contractility, excitability, extensibility, and elasticity. Test your knowledge on how muscles operate within the body!

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