Neuromuscular Junction and Muscle Contraction
34 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the role of troponin in muscle contraction?

  • It facilitates the breakdown of ATP for energy.
  • It binds calcium and prevents tropomyosin from uncovering G actin active sites. (correct)
  • It anchors tropomyosin to myosin.
  • It prevents calcium release from the sarcoplasmic reticulum.

    • Which sequence best describes the steps of muscle relaxation?

  • Acetylcholine release, myosin head attachment, shortening of muscle.
  • Calcium release, acetylcholine release, cross-bridge formation.
  • Cessation of action potential, calcium diffusion from troponin, tropomyosin covering G actin. (correct)
  • Action potential propagation, calcium diffusion, tropomyosin uncovering.

    • During contraction, what role do myosin heads play?

  • They serve as the primary energy source for muscle contraction.
  • They bind to active sites on actin molecules to form cross bridges. (correct)
  • They transport calcium ions into the muscle fibers.
  • They control the release of neurotransmitters at the neuromuscular junction.

    • What occurs during isometric contractions?

    <p>Muscle tension increases without a change in length.</p> Signup and view all the answers

    What happens at the triad during excitation-contraction coupling?

    <p>Electrical signals trigger the release of calcium from the sarcoplasmic reticulum.</p> Signup and view all the answers

    Which of the following describes muscle atrophy?

    <p>Age-related reduction in muscle mass</p> Signup and view all the answers

    Which mechanism is NOT involved in muscle fatigue?

    <p>Increased motor neuron activity</p> Signup and view all the answers

    What is a common cause of muscle soreness after vigorous exercise?

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

    What causes skeletal muscle cramps?

    <p>Ion imbalance</p> Signup and view all the answers

    Which condition is characterized by chronic widespread pain in skeletal muscles?

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

    What type of disease is Myasthenia Gravis?

    <p>Autoimmune disease</p> Signup and view all the answers

    Duchenne Muscular Dystrophy primarily affects which group of muscles initially?

    <p>Hip muscles</p> Signup and view all the answers

    Which diagnostic test is NOT commonly used for Duchenne Muscular Dystrophy?

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

    Which statement accurately describes a feature of myosin?

    <p>The head of myosin molecule binds to an active site on G actin</p> Signup and view all the answers

    What structure invaginates into the interior of skeletal muscle fibers?

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

    What type of muscle contraction occurs when a weight lifter is unable to move the weight?

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

    In the process of muscle contraction, which event occurs first?

    <p>Troponin binds to calcium</p> Signup and view all the answers

    What is the role of ATPase found in muscle contraction?

    <p>Hydrolyzing ATP to provide energy for muscle contraction</p> Signup and view all the answers

    What happens after calcium ions bind to troponin?

    <p>Troponin pulls tropomyosin away from actin</p> Signup and view all the answers

    Which component is primarily responsible for calcium ion storage in muscle cells?

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

    Which role does actin play during muscle contraction?

    <p>Actin serves as a site for myosin binding</p> Signup and view all the answers

    What is the first step in the initiation of muscle contraction at the neuromuscular junction?

    <p>Acetylcholine is released into the synaptic cleft by exocytosis</p> Signup and view all the answers

    Which molecule prevents tropomyosin from uncovering the G actin active sites in a relaxed muscle?

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

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

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

    What role does acetylcholinesterase play in muscle contraction?

    <p>It removes acetylcholine from the synaptic cleft</p> Signup and view all the answers

    Which component of the actin myofilament serves to cover active sites on G actin subunits when the muscle is relaxed?

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

    What is the primary role of acetylcholine at the neuromuscular junction?

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

    Which of the following correctly describes the synaptic cleft?

    <p>A gap separating axonal ends and muscle fibers</p> Signup and view all the answers

    What initiates the opening of voltage-gated calcium channels at the neuromuscular junction?

    <p>Depolarization caused by action potential</p> Signup and view all the answers

    The muscle plasma membrane at the neuromuscular junction is referred to as what?

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

    Which structure contains synaptic vesicles that hold acetylcholine?

    <p>Axonal endings</p> Signup and view all the answers

    What condition is primarily affected at the neuromuscular junction in myasthenia gravis?

    <p>Loss of acetylcholine receptors</p> Signup and view all the answers

    What occurs after the action potential reaches the presynaptic terminal?

    <p>Calcium influx triggers neurotransmitter release</p> Signup and view all the answers

    What is the main function of the muscular system as mentioned in the learning outcome?

    <p>To enable movement and maintain posture</p> Signup and view all the answers

    Study Notes

    Neuromuscular Junction

    • The neuromuscular junction is where nerve cells stimulate muscle cells.
    • It is formed by axonal endings, containing synaptic vesicles with acetylcholine, and the motor end plate, which is the muscle plasma membrane in the area of the junction with acetylcholine receptors.
    • Axonal ends and muscle fibers are separated by a gap called the synaptic cleft.

    Physiology of Muscle Contraction

    • Muscle contraction at the neuromuscular junction occurs in 9 steps:
      • Action potential arrives, opening voltage-gated calcium channels in the presynaptic membrane.
      • Calcium ions initiate the release of acetylcholine from synaptic vesicles.
      • Acetylcholine is released into the synaptic cleft by exocytosis.
      • Acetylcholine binds to ligand-gated sodium channels on the motor end plate.
      • Ligand-gated sodium channels open, allowing sodium to enter the muscle fiber.
      • Acetylcholine detaches from the ligand-gated channels which close.
      • Acetylcholinesterase removes acetylcholine from the synaptic cleft.
      • Choline is transported back into the presynaptic terminal with sodium.
      • Acetylcholine is reformed inside the presynaptic terminal.

    Actin and Myosin Myofilament Structure

    • Actin myofilaments are composed of globular (G) actin, which forms fibrous (F) actin, tropomyosin, which covers the active sites on G actin in relaxed muscles, and troponin, which anchors to actin, prevents tropomyosin from uncovering G actin sites, and binds calcium.
    • Myosin myofilaments are made up of myosin molecules with two heavy chains, two heads that bind to active sites on actin forming cross bridges, and a rod portion attached to the heads by a hinge region.
    • Myosin heads are also ATPase enzymes.

    Excitation-Contraction Coupling

    • Excitation-contraction coupling occurs at the triad.
    • In order to contract, skeletal muscle must be stimulated by a nerve ending, propagate action potential along its sarcolemma, and have an increase in intracellular calcium levels which trigger contraction.

    Cross-Bridge Movement

    • Calcium binds to troponin, causing tropomyosin to move and expose the active sites on actin.
    • The myosin heads bind to the actin, forming cross bridges.
    • The myosin heads then pivot, pulling the actin filaments towards the center of the sarcomere.
    • ATP is used to detach the myosin heads from the actin, and the process repeats as long as calcium is present.
    • Muscle relaxation happens when acetylcholine stops being released at the neuromuscular junction, action potential ceases on the sarcolemma, calcium diffuses away from troponin, tropomyosin covers G actin active sites, and cross bridge formation stops.

    Types of Muscle Contractions

    • Isometric contractions involve muscle tension increasing without shortening.
    • Isotonic contractions involve muscle shortening with constant tone, and are further categorized into concentric and eccentric contractions.

    Disorders of the Muscular System

    • Aging: Muscle atrophy, a reduction in muscle mass and regulation of muscle function, is a physiological condition that occurs with age.
    • Muscle Fatigue: Fatigue is a temporary state of reduced work capacity that can be caused by acidosis, ATP depletion, oxidative stress, and local inflammatory responses.
    • Muscle Soreness: Soreness after exercise is caused by an inflammatory chemical influx into the muscle fibers.
    • Cramps: Painful, spastic contractions of skeletal muscle can occur due to dehydration and ion imbalances.
    • Tendinitis: Inflammation of a tendon or its attachment point due to overuse.
    • Fibromyalgia: Chronic widespread pain in skeletal muscles with no known cure.
    • Myasthenia Gravis: Autoimmune disease in which autoantibodies bind to acetylcholine receptors.
    • Duchenne Muscular Dystrophy: Inherited disorder involving mutations in the dystrophin gene, leading to progressive muscle weakness and contractures.

    Diagnostic Tests of the Muscular System

    • Electromyography
    • Serum creatinine
    • Muscle biopsies
    • Immunohistochemical studies

    Formative Assessment

    • The answer to question 1 is e. Secretability.
    • The answer to question 2 is b. The head of myosin molecule binds to an active site on G actin.
    • The answer to question 3 is a. T tubule.
    • The answer to question 4 is b. Isometric contraction.
    • The answer to question 5 is c. 2,3,7.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Unit 5.2 The Muscular System PDF

    Description

    This quiz covers the neuromuscular junction and the physiology of muscle contraction in detail. Learn about the roles of acetylcholine and the step-by-step process of muscle activation. It's essential for understanding how nerve signals stimulate muscle movement.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser