Muscle Fiber Structure and TEM Analysis
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Questions and Answers

What is the primary structural component of thick filaments in myofibrils?

  • Myosin (correct)
  • Tropomyosin
  • Calmodulin
  • Actin

    • Which region is specifically described as being bisected by a Z disc?

  • A band
  • H zone
  • M line
  • I band (correct)

    • Which part of the myofibril is characterized by a lighter zone corresponding to myosin without thin filaments?

  • M line
  • Z line
  • A band
  • H zone (correct)

    • What structure marks the center of the H zone?

    <p>M line</p> Signup and view all the answers

    What is the width of thick filaments within the myofibrils?

    <p>15 nm</p> Signup and view all the answers

    Which component fills the regions around the Z line within the I bands?

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

    What type of proteins primarily make up the heavy chains of myosin?

    <p>Motor proteins</p> Signup and view all the answers

    Which of the following processes is crucial for the binding of myosin heads to actin?

    <p>Actomyosin ATPase activity</p> Signup and view all the answers

    What type of muscle fibers are characterized by rapid, short-term contractions and low mitochondrial content?

    <p>Type IIb - Fast, Glycolytic Fibers</p> Signup and view all the answers

    Which muscle fiber type is best adapted for endurance and prolonged activity without fatigue?

    <p>Type I - Slow Oxidative Fibers</p> Signup and view all the answers

    Which muscle fiber type demonstrates the ability to switch between aerobic and anaerobic respiration?

    <p>Type IIa - Fast, Oxidative-Glycolytic Fibers</p> Signup and view all the answers

    What characteristic feature distinguishes Type IIb muscle fibers from Type I and IIa fibers?

    <p>Lower fatigue resistance</p> Signup and view all the answers

    Which feature is NOT associated with Type I - Slow Oxidative fibers?

    <p>Rapid fatigue</p> Signup and view all the answers

    What metabolic process do Type IIb fibers primarily rely on for energy production?

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

    The color of fast glycolytic fibers is typically described as:

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

    Which type of muscle fibers would be found in a sprinter's legs due to their need for rapid strength and speed?

    <p>Type IIb - Fast, Glycolytic Fibers</p> Signup and view all the answers

    What initiates a muscle impulse at the neuromuscular junction?

    <p>Binding of ACh to receptors in the myofibrils</p> Signup and view all the answers

    What role do calcium ions play in muscle contraction?

    <p>They bind to troponin, causing a conformational change</p> Signup and view all the answers

    What is the function of the T-tubules in muscle fibers?

    <p>To transmit nerve impulses rapidly to the muscle fiber</p> Signup and view all the answers

    What mechanism allows myosin heads to attach to actin during muscle contraction?

    <p>Exposure of active sites on actin after tropomyosin movement</p> Signup and view all the answers

    How do Schwann cells contribute to muscle fiber innervation?

    <p>By enclosing small axon branches and facilitating neurotransmitter release</p> Signup and view all the answers

    What structure does ACh bind to after its release at the neuromuscular junction?

    <p>The motor end plate of the neuromuscular junction</p> Signup and view all the answers

    What happens after calcium ions bind to troponin during muscle contraction?

    <p>Tropomyosin changes shape, exposing actin's active sites</p> Signup and view all the answers

    What is the significance of the external lamina of Schwann cells in muscle fiber innervation?

    <p>It fuses with the sarcolemma for efficient neurotransmission</p> Signup and view all the answers

    What is the primary protein component of thin filaments?

    <p>F-actin</p> Signup and view all the answers

    How are thin filaments anchored in muscle fibers?

    <p>By actin-binding proteins at the Z disc</p> Signup and view all the answers

    What does troponin consist of?

    <p>Three subunits: TnT, TnC, and TnI</p> Signup and view all the answers

    What initiates the release of calcium from the sarcoplasmic reticulum?

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

    Which statement about the configuration of thin filaments is correct?

    <p>They are associated with oppositely polarized ends.</p> Signup and view all the answers

    What specialized structure facilitates the release of calcium ions into the cytoplasm?

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

    What is the function of tropomyosin in muscle contraction?

    <p>To stabilize the active sites on actin</p> Signup and view all the answers

    What is the length and width of a thin filament?

    <p>1.0 μm long and 8 nm wide</p> Signup and view all the answers

    What is a notable characteristic of smooth muscle cells when they contract?

    <p>Their borders become scalloped.</p> Signup and view all the answers

    Which statement about the structure of smooth muscle fibers is correct?

    <p>They are elongated, tapering, and non-striated.</p> Signup and view all the answers

    What role do gap junctions play in smooth muscle cells?

    <p>They allow for communication between adjacent muscle cells.</p> Signup and view all the answers

    How are smooth muscle fibers primarily controlled?

    <p>Through autonomic nerves and hormones.</p> Signup and view all the answers

    What effect does smooth muscle contraction have on the cell length?

    <p>It decreases the length of the cells.</p> Signup and view all the answers

    In which locations is smooth muscle predominantly found?

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

    What type of muscle is also referred to as visceral muscle?

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

    What structural element is concentrated near the nuclei of smooth muscle fibers?

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

    Study Notes

    Muscle Tissue Overview

    • Myofibrils show a repetitive arrangement of sarcomeres, characterized by transverse striations.
    • Sarcomeres exhibit the A band, H zone, and I band structure.
    • I bands contain sarcoplasm, mitochondria, glycogen, and smooth endoplasmic reticulum around the Z line.

    Thick Filaments

    • Thick filaments are approximately 1.6 μm long and 15 nm wide, primarily composed of myosin.
    • Myosin includes two heavy chains and two pairs of light chains, with myosin heads capable of binding actin.
    • ATP facilitates energy release in the actomyosin interaction.

    A Bands, H Zone, and I Bands

    • A bands consist of thick filaments and overlapping thin filaments; they are darker in appearance.
    • H zone is the lighter central region of the A band with only myosin rod-like portions.
    • I bands are lighter zones bisected by Z discs, containing non-overlapping thin filaments.

    Thin Filaments

    • Thin filaments measure 1.0 μm long and 8 nm wide, coiled and composed of F-actin.
    • They are anchored on the Z disc by actin-binding proteins and tightly associate with regulatory proteins: tropomyosin and troponin.

    Sarcoplasmic Reticulum & T Tubules

    • Sarcoplasmic reticulum specializes in calcium ion sequestration.
    • Depolarization of the sarcoplasmic reticulum membrane releases calcium ions, initiating contraction.
    • Transverse (T) tubules penetrate deeply into the sarcoplasm and encircle myofibrils at the A and I band boundaries.

    Triad Structure

    • The triad consists of a T tubule flanked by two terminal cisternae of the sarcoplasmic reticulum.
    • Upon depolarization, calcium ions release into the cytoplasm, enabling actin-myosin interaction.

    Muscle Contraction Mechanism

    • A nerve impulse releases acetylcholine (ACh), causing muscle impulses and subsequent contraction.
    • Calcium binds to troponin, exposing active sites on actin, allowing myosin heads to form cross bridges.

    Innervation of Muscle

    • Myelinated motor nerves form branches within perimysium, giving rise to unmyelinated terminals that synapse with muscle fibers.
    • Schwann cells enclose axon branches and fuse their external lamina with the sarcolemma of muscle cells.

    Skeletal Muscle Fiber Types

    • Type I (Slow Oxidative): Specialized for long, fatigue-resistant contractions; rich in mitochondria and myoglobin, using aerobic respiration.
    • Type IIa (Fast, Oxidative-Glycolytic): Intermediate features between Type I and Type IIb; primarily uses aerobic respiration but can switch to anaerobic.
    • Type IIb (Fast, Glycolytic): Tailored for quick, intense contractions; fewer mitochondria and capillaries, reliant on anaerobic glycolysis, leading to rapid fatigue.

    Smooth Muscle Characteristics

    • Also known as visceral muscle; involved in involuntary contractions in various organs.
    • Features elongated, non-striated cells with tapering ends, connected by gap junctions.
    • Contains prominent mitochondria, polyribosomes, and a network of reticular fibers; contraction deforms nuclei into a corkscrew shape.

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    Description

    This quiz delves into the intricate structure of myofibrils, focusing on the electron-dense A bands and the H zone. It explores how the arrangement of sarcomeres and the surrounding structures contribute to the overall muscle fiber characteristics. Test your knowledge on muscle anatomy and histology!

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