Recent

  • Show all results for ""
Muscle Structure and Function Quiz
40 Questions
0 Views

Muscle Structure and Function Quiz

Created by
@WieldyEpic

Questions and Answers

What role do costameres play in muscle cells?

  • They facilitate the contraction of myofibrils.
  • They connect the contractile elements to the extracellular matrix. (correct)
  • They increase the width of the A band during contraction.
  • They store calcium ions for muscle contraction.

    • Which structure remains unchanged in width during muscle contraction?

  • Z disk
  • H zone
  • I band
  • A band (correct)

    • What triggers the power stroke during the crossbridge cycle?

  • The conformational change of actin.
  • The binding of myosin to actin in the presence of Ca2+. (correct)
  • The release of ATP from myosin.
  • The hydrolysis of ADP.

    • What happens to intracellular calcium levels when a muscle is not stimulated?

    <p>They drop, stopping the contraction cycle.</p> Signup and view all the answers

    Which phase of the crossbridge cycle involves myosin releasing actin?

    <p>Release phase after ATP binding</p> Signup and view all the answers

    How does rigor mortis occur from a biochemical standpoint?

    <p>ATP depletion prevents myosin from detaching from actin.</p> Signup and view all the answers

    When Ca2+ levels are maintained, what effect does that have on muscle contraction?

    <p>Contraction intensity increases with continuous cycles.</p> Signup and view all the answers

    What is the primary result of multiple power strokes occurring in a series?

    <p>The total shortening and tension in the muscle increase.</p> Signup and view all the answers

    What happens when the sarcomere length becomes too long?

    <p>Crossbridge formation is prevented.</p> Signup and view all the answers

    How does the velocity of muscle shortening change with increasing load?

    <p>It decreases as load increases.</p> Signup and view all the answers

    What occurs when muscle load surpasses the maximum load?

    <p>The muscle lengthens, resulting in eccentric contraction.</p> Signup and view all the answers

    What is the relationship between maximum power and load?

    <p>Maximum power is reached at about a third of maximum load.</p> Signup and view all the answers

    Which type of muscle exhibits the highest energy efficiency?

    <p>Smooth muscles.</p> Signup and view all the answers

    How can the force of skeletal muscle contraction be modulated extrinsically?

    <p>By increasing the frequency of nerve impulses.</p> Signup and view all the answers

    What does the term 'tetanus' refer to in muscle contraction?

    <p>A contraction that occurs before full relaxation.</p> Signup and view all the answers

    What remains unchanged when initial muscle length is altered?

    <p>Y-intercept of muscle velocity.</p> Signup and view all the answers

    What is the primary mechanism responsible for the reduction of intracellular Ca2+ concentration during muscle relaxation?

    <p>Sarcoplasmic and endoplasmic reticulum calcium ATPase (SERCA)</p> Signup and view all the answers

    What happens to sarcomere length when muscle contraction occurs isometrically at different lengths?

    <p>The force of contraction varies with the initial length of the muscle</p> Signup and view all the answers

    Which of the following best describes isometric contraction?

    <p>Sarcomeres shorten with length fixed, increasing tension</p> Signup and view all the answers

    What is the role of calsequestrin in muscle contraction?

    <p>Buffers calcium ions in the sarcoplasmic reticulum</p> Signup and view all the answers

    During muscle contraction, what occurs when sarcomere length exceeds 2.0 µm?

    <p>Force production decreases significantly</p> Signup and view all the answers

    Which transporters contribute to the reduction of intracellular Ca2+ concentration in muscle cells?

    <p>Na/Ca exchanger and plasma membrane Ca ATPase</p> Signup and view all the answers

    What is the effect of lower than optimal sarcomere lengths on muscle contraction?

    <p>There is interference with crossbridge formation</p> Signup and view all the answers

    Which component of muscle tension is a result of structural elements being stretched?

    <p>Passive tension</p> Signup and view all the answers

    What is the primary mechanism by which unitary smooth muscle cells communicate and contract as a functional unit?

    <p>By electrical coupling via gap junctions.</p> Signup and view all the answers

    Which of the following is an example of tonic smooth muscle?

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

    What primarily triggers action potentials in smooth muscle cells?

    <p>Raising membrane potential above a threshold.</p> Signup and view all the answers

    What is the significance of Ca2+ in smooth muscle contraction compared to skeletal muscle?

    <p>Extracellular Ca2+ is more crucial for smooth muscle contraction.</p> Signup and view all the answers

    In which situation would smooth muscle exhibit stress relaxation?

    <p>After an initial contraction followed by gradual relaxation.</p> Signup and view all the answers

    Which characteristic differentiates smooth muscle action potentials from those in skeletal muscle?

    <p>Calcium ions mainly trigger depolarization in smooth muscle.</p> Signup and view all the answers

    What occurs to blood vessels during autoregulation when they are stretched due to increased blood pressure?

    <p>They experience constriction.</p> Signup and view all the answers

    Which statement describes the nature of phasic smooth muscles?

    <p>They contract rhythmically or transiently upon stimulation.</p> Signup and view all the answers

    What type of myosin ATPase is found in slow-twitch muscle fibers?

    <p>Slow type I myosin ATPase</p> Signup and view all the answers

    Which type of muscle fibers is more resistant to fatigue?

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

    How are slow-twitch fibers characterized in terms of motor units?

    <p>Innervated by smaller motor neurons forming smaller motor units</p> Signup and view all the answers

    Which type of muscle fibers can be further classified as type IIa and IIb?

    <p>Fast-twitch fibers</p> Signup and view all the answers

    What is the primary feature of multiunit smooth muscles?

    <p>Each cell contracts independently due to lack of electrical connection.</p> Signup and view all the answers

    What distinguishes the arrangement of thick and thin filaments in smooth muscle from other muscle types?

    <p>They are arranged in different directions anchored to dense bodies.</p> Signup and view all the answers

    What is the role of caveolae in smooth muscle cells?

    <p>They serve as the equivalent of T-tubules.</p> Signup and view all the answers

    Which type of muscle fibers is primarily involved in postural stability?

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

    Study Notes

    Structure of Sarcomeres and Costameres

    • Actin filaments attach to Z-disks through binding to α-actinin.
    • Z-disks serve as anchorage points for myofilaments and are connected by intermediate filament proteins.
    • Costameres link Z-disks to the sarcolemma, stabilizing muscle structure and facilitating mechanical linkage.
    • Costameres contain proteins such as dystroglycans and integrins that interact with extracellular matrix proteins like laminin and fibronectin.
    • Mutations in these structural proteins can lead to muscular diseases.

    Sliding Filament Theory

    • When a sarcomere shortens, the A band remains constant, while the I band and H zone become narrower.
    • The sliding filament theory posits that myosin and actin filaments slide past each other, reducing the distance between Z-lines during contraction.

    Contractile Cycle

    • The contractile cycle is triggered by calcium ions (Ca2+).
    • Steps in the cross-bridge cycle:
      • Myosin binds to actin in the presence of Ca2+.
      • Myosin head pivots, pulling the actin towards the sarcomere center (power stroke) and releasing ADP.
      • ATP binding causes myosin to release from actin.
      • Myosin ATPase hydrolyzes ATP, repositioning the myosin head for another cycle.
    • Ca2+ serves as a crucial regulator; intracellular Ca2+ concentration decreases when muscles are not stimulated.
    • Rigor mortis occurs when ATP levels drop, halting the cycle during contraction.

    Tension Development

    • Shortening and tension production are cumulative across the number of sarcomeres and myofibrils in a muscle fiber.
    • Muscle tension consists of active tension (from sarcomere shortening) and passive tension (stretching structural elements).

    Types of Contraction

    • Isometric contraction: Muscle length stays fixed; tension increases as sarcomeres shorten.
    • Isotonic contraction: Muscle length changes while tension remains constant.
    • The length-tension relationship indicates optimal lengths (~2.0 µm) for maximum force generation.

    Contraction Mechanics

    • Muscle shortening velocity is inversely related to load; maximum velocity occurs at zero load.
    • Beyond maximum load, muscles experience eccentric contraction (lengthening) instead of concentric contraction (shortening).

    Muscle Fiber Types and Fatigue

    • Fast-twitch fibers (type II) contract faster and stronger but fatigue more quickly than slow-twitch fibers (type I).
    • Slow-twitch fibers have higher oxidative capacity and are more resistant to fatigue.
    • Motor neurons innervating slow-twitch fibers form smaller motor units for finer control, while fast-twitch fibers form larger motor units.

    Smooth Muscle Characteristics

    • Smooth muscle differs from skeletal and cardiac muscles in filament arrangement and regulation.
    • Acts are anchored to dense bodies instead of Z-disks, using caveolae for T-tubule equivalent functions.
    • Multiunit smooth muscles contract independently, while unitary smooth muscles function together as functional syncytia.
    • Tonic smooth muscles maintain constant tension, phasic smooth muscles contract rhythmically.

    Contraction Regulation in Smooth Muscle

    • Smooth muscle contraction involves various stimuli and relies heavily on extracellular Ca2+.
    • Different pathways for Ca2+ entry: voltage-gated channels, ryanodine receptors, and IP3-mediated release from the SR.
    • Smooth muscle action potentials can vary; they might rely on Ca2+ instead of Na+ for depolarization.
    • Autoregulation mechanisms in blood vessels cause vasoconstriction or vasodilation based on mechanical stimuli.
    • Stress relaxation phenomenon occurs in organs with storage functions, showing initial contraction followed by gradual relaxation.

    Studying That Suits You

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

    Quiz Team

    Related Documents

    SF018-021_Muscle_Physiology.pdf

    Description

    Test your knowledge on the structure of sarcomeres, costameres, and the sliding filament theory. This quiz covers key concepts related to muscle contraction, including the role of structural proteins and the contractile cycle. Perfect for students of biology and anatomy.

    More Quizzes Like This

    T3 L2: Physiology of Skeletal Muscle Contraction (HJW)
    89 questions

    T3 L2: Physiology of Skeletal Muscle Contraction (HJW)

    ProlificSynergy avatar
    ProlificSynergy
    Skeletal Muscle Structure and Function Quiz
    10 questions

    Skeletal Muscle Structure and Function Quiz

    FeistyForesight avatar
    FeistyForesight
    Human Physiology Chapter on Muscle Structure
    40 questions

    Human Physiology Chapter on Muscle Structure

    StableEpilogue avatar
    StableEpilogue
    Muscle Fiber Structure and TEM Analysis
    40 questions

    Muscle Fiber Structure and TEM Analysis

    VeritableJadeite avatar
    VeritableJadeite
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser