Muscle Anatomy and Function
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Questions and Answers

What triggers the activation of ryanodine receptors on the sarcoplasmic reticulum?

  • Voltage-gated sodium channels
  • Calcium ions binding to troponin
  • Mechanical coupling with DHP receptors (correct)
  • Action potentials in muscle fibers

    • Which type of contraction occurs when muscle develops tension without changing its length?

  • Concentric contraction
  • Eccentric contraction
  • Isotonic contraction
  • Isometric contraction (correct)

    • Which calcium sensor is found in smooth muscle?

  • Calmodulin (correct)
  • Calcium-binding protein
  • Ryr receptor
  • Troponin

    • Which feature distinguishes skeletal muscle from cardiac muscle?

    <p>Multinucleated cells</p> Signup and view all the answers

    What characterizes eccentric contraction?

    <p>Load exceeds muscle tension, lengthening muscle</p> Signup and view all the answers

    What is the primary function of cardiac muscle?

    <p>Pump blood</p> Signup and view all the answers

    Which structure is responsible for storing calcium ions in muscle cells?

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

    What type of muscle is characterized by being striated and voluntary?

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

    What is the contractile unit of a muscle fiber called?

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

    In skeletal muscle, what does the I-band represent?

    <p>A light area containing only actin filaments</p> Signup and view all the answers

    What is the primary advantage of muscle lever systems mentioned in the content?

    <p>Increased manoeuvrability</p> Signup and view all the answers

    What are the extensions of the cell membrane in muscle fibers called?

    <p>T-tubules</p> Signup and view all the answers

    What is a characteristic of smooth muscle?

    <p>Involuntary control</p> Signup and view all the answers

    What happens during muscle contraction in relation to the A-band?

    <p>The A-band remains the same length.</p> Signup and view all the answers

    Which component wraps around actin and covers the myosin-binding site?

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

    What is the effect of ATP during the cross-bridge cycle?

    <p>It provides energy for movement and breaks the actin-myosin link.</p> Signup and view all the answers

    If the z-lines are too close to actin filaments, what is a negative effect?

    <p>Too much overlap preventing cross-bridge cycling.</p> Signup and view all the answers

    What is the optimal range of overlap for actin and myosin filaments?

    <p>2.0-2.2</p> Signup and view all the answers

    What structural feature distinguishes myosin filaments?

    <p>Their heads protrude and tails wrap around each other.</p> Signup and view all the answers

    What is a function of troponin in muscle contraction?

    <p>To bind calcium ions and regulate the binding of myosin to actin.</p> Signup and view all the answers

    Which part of the sarcomere is characterized by only myosin filaments?

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

    What role does calcium play in muscle contraction?

    <p>Calcium binds to the TnC subunit of troponin, facilitating contraction.</p> Signup and view all the answers

    Which statement describes a twitch in muscle fibers?

    <p>A twitch is a single, brief contraction in response to one action potential.</p> Signup and view all the answers

    What happens to tropomyosin when calcium binds to the troponin complex?

    <p>Tropomyosin moves deeper into the actin groove, exposing myosin binding sites.</p> Signup and view all the answers

    What is the latent period in muscle contraction?

    <p>The delay between action potential arrival and muscle contraction onset.</p> Signup and view all the answers

    Which component blocks myosin binding sites on actin in a relaxed muscle?

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

    How many binding sites for calcium are available on the TnC subunit of troponin?

    <p>Two high affinity and two low affinity binding sites.</p> Signup and view all the answers

    What initiates the release of acetylcholine at the neuromuscular junction?

    <p>The arrival of an action potential.</p> Signup and view all the answers

    Tetanus occurs when which of the following takes place?

    <p>A muscle fiber is stimulated repeatedly at a high frequency.</p> Signup and view all the answers

    Study Notes

    Muscle Contractions

    • Muscle contractions are the mechanisms of animal movement
    • Amoeboid movement: Cells change shape to move forward (e.g., eosinophils in immune cells)
    • Ciliary and flagellar bending: Movement from cilia and flagella

    Muscle Tissue Types

    • Skeletal: Striated, voluntary, responsible for movement, heat production, and increased manoeuvrability
    • Cardiac: Striated, involuntary, pumps blood
    • Smooth: Non-striated, involuntary, controls organ size and movement

    Muscle Lever Systems

    • Muscle lever systems work at a mechanical disadvantage
    • Muscle fibers are wrapped in connective tissue (epimysium) for mechanical support

    Skeletal Muscle Architecture

    • Muscle fibers are wrapped in connective tissue (epimysium, perimysium, endomysium)
    • Arrangement: Muscle belly, tendon, single muscle fiber, fasciculus, capillary, sarcolemma, sarcoplasm, nuclei

    Specialized Membranes of Skeletal Muscle

    • Myofibrils: Long, thread-like structures containing myosin and actin. Organized into sarcomeres, which causes striations
    • Sarcolemma: Cell membrane, has openings for T-tubules to reach inside the cell
    • T-tubules: Extensions of the cell membrane that allow action potentials to reach muscle fibers and release calcium ions
    • Sarcoplasmic Reticulum (SR): Stores calcium ions. Contains terminal cisternae on either side of T tubules (collectively called a triad).
    • Triad: Important for excitation-contraction coupling

    Myofibril Structure

    • Sarcomere: Basic contractile unit of a myofibril
      • I-band (isotropic): Light band, only actin filaments
      • A-band (anisotropic): Dark band, overlapping actin and myosin filaments
      • Z-line: Located in the center of the I-band; the distance between adjacent Z-lines defines a sarcomere
      • H-zone: Center of the A-band, only myosin filaments
      • M-line: Middle of the sarcomere
    • Myosin: Thick filament
    • Actin: Thin filament
    • Titin, Nebulin: Accessory proteins important for maintaining the architecture of myofibrils

    The Sliding Filament Mechanism

    • Each cross-bridge generates force independently of other cross-bridges
    • Force is determined by the number of cross-bridges formed between myosin and actin filaments; force is also determined by the amount of overlap between myosin and actin filaments

    Sarcomere Length-Tension Relationship

    • Optimal range: 2.0-2.2 μm; allows actin and myosin overlap and produces maximal force efficiently
    • Too short or too long causes insufficient overlap for optimal force generation

    The Cross-Bridge Cycle

    • ATP hydrolysis energizes the cross-bridge
    • Cross-bridge binds to actin, causing a power stroke
    • ATP binds to myosin, causing the cross-bridge to detach.

    ATP as an Allosteric Regulator

    • ATP is essential, it's energy source for cross-bridge movement
    • Binding of ATP to myosin regulates the cycle by breaking the link between actin and myosin

    Calcium-Ion Regulation

    • Calcium ions initiate contraction by binding to troponin.
    • This binding moves tropomyosin, uncovering the myosin binding sites on actin to initiate contraction

    Twitch and Tetanus

    • Twitch: Brief contraction in response to a single action potential
    • Tetanus: Sustained contraction from repeated stimulation; can be unfused (incomplete) or fused (complete)

    Membrane Receptors in Triads

    • DHP receptor: Voltage sensor
    • Ryanodine receptor: Calcium release channel

    Mechanism of Calcium Release from the Sarcoplasmic Reticulum

    • Action potentials cause calcium release from the SR into the cytoplasm
    • Calcium binding to troponin initiates contraction

    Isometric and Isotonic Contraction

    • Isometric: Muscle tension without length change
    • Isotonic: Muscle shortens while maintaining constant load. Eccentric contraction involves muscle lengthening under load

    Heart Muscle Structure

    • Contains intercalated disks (specialized cell junctions)
    • Desmosomes hold cells together.
    • Gap junctions allow for rapid transmission of electrical impulses between cells

    EC Coupling in Cardiac Muscle

    • Action potentials cause Ca2+ release from the sarcoplasmic reticulum
    • Activation of ryanodine receptors to initiate calcium release
    • Na+/Ca2+ exchangers pump Ca2+ out of the muscle to relax.

    Smooth Muscle

    • Unitary: Muscle fibers contract together
    • Multiunit: Muscle fibers contract independently
    • Has Dense bodies
    • Ca2+ binding to calmodulin activates myosin light chain kinase, initiates contraction

    Regulation of Contraction in Different Muscle Types

    • The mechanisms for regulating contraction is based on different types of muscles
    • Calcium binding to troponin in skeletal and cardiac muscle
    • Calcium binding to calmodulin in smooth muscle

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    Muscle Physiology PDF

    Description

    This quiz covers the key concepts related to muscle contractions, tissue types, lever systems, and architecture of skeletal muscle. Understand how different muscle types contribute to movement and how muscle fibers are structured for optimal function. Prepare to test your knowledge on the mechanics of animal movement and muscle physiology.

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