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Muscle Tissue Overview
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Muscle Tissue Overview

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@VeritableJadeite

Questions and Answers

What is the role of junctional folds in muscle cells?

  • They facilitate neurotransmitter degradation.
  • They provide structural support to the muscle.
  • They increase the postsynaptic surface area. (correct)
  • They reduce the number of transmembrane receptors.

    • What is found concentrated near the nucleus in muscle cells?

  • Actin filaments and myosin heads.
  • Synaptic vesicles containing dopamine.
  • Mitochondria and polyribosomes. (correct)
  • Neurotransmitter receptors.

    • How are the borders of smooth muscle cells affected during contraction?

  • They maintain their shape and size.
  • They detach from neighboring cells.
  • They become elongated and straight.
  • They become scalloped and the nucleus distorts. (correct)

    • What structures do Schwann cells form at the neuromuscular junction?

    <p>They enclose axon branches and contact points.</p> Signup and view all the answers

    What are caveolae and their association with smooth muscle cells?

    <p>They are shallow membrane invaginations frequent at the surface.</p> Signup and view all the answers

    What role do calcium ions play in muscle contraction?

    <p>They bind to troponin and expose active sites on actin.</p> Signup and view all the answers

    Which skeletal muscle fiber type is described as having the least resistance to fatigue?

    <p>Type IIb fibers</p> Signup and view all the answers

    What role does acetylcholine play at the motor end plate?

    <p>It diffuses across the cleft and binds to receptors on the sarcolemma.</p> Signup and view all the answers

    Which statement accurately describes Type IIa skeletal muscle fibers?

    <p>They are optimized for short-term, rapid contractions.</p> Signup and view all the answers

    Which cellular structure is primarily responsible for inserting into dense bodies to transmit contractile force in smooth muscle?

    <p>Desmin intermediate filaments</p> Signup and view all the answers

    What is the primary composition of thick filaments in muscle fibers?

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

    What is the sequence of events occurring during the muscle contraction cycle starting from calcium binding?

    <p>Calcium binds to troponin, tropomyosin shifts, and myosin heads pivot.</p> Signup and view all the answers

    What initiates the muscle impulse at the neuromuscular junction (NMJ)?

    <p>ACh binding to receptors at the motor end plate.</p> Signup and view all the answers

    What prevents smooth muscle fibers from being under voluntary control?

    <p>Their lack of motor end plates</p> Signup and view all the answers

    How long are the thick filaments in muscle fibers?

    <p>1.6 µm</p> Signup and view all the answers

    Which of the following statements is true regarding Type I skeletal muscle fibers?

    <p>They are suited for endurance activities due to aerobic respiration.</p> Signup and view all the answers

    Which component is NOT found in the muscle action potential pathway at the motor end plate?

    <p>Serotonin neurotransmitters</p> Signup and view all the answers

    What structural feature do the heavy chains of myosin share?

    <p>They are identical and twisted together</p> Signup and view all the answers

    During muscle contraction, what happens to the sarcomeres?

    <p>They shorten as thick and thin filaments slide past each other.</p> Signup and view all the answers

    What characterizes the intermediate filaments in smooth muscle cells?

    <p>They are typically composed of desmin.</p> Signup and view all the answers

    What is indicated by the presence of myosin heads on thick filaments?

    <p>They bind to both actin and ATP for energy release</p> Signup and view all the answers

    Which characteristic is unique to Type IIb fibers among the skeletal muscle fiber types?

    <p>They primarily rely on anaerobic glycolysis for energy.</p> Signup and view all the answers

    What is the width of thick filaments?

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

    How does the influx of Na+ affect the sarcolemma upon acetylcholine binding?

    <p>It leads to depolarization of the sarcolemma, generating a muscle action potential.</p> Signup and view all the answers

    In which region of the sarcomere do thick filaments occupy?

    <p>A band</p> Signup and view all the answers

    What are dense bodies in smooth muscle functionally similar to?

    <p>Z discs in striated muscle</p> Signup and view all the answers

    Which statement is true regarding the control of smooth muscle contraction?

    <p>Hormones and local physiologic alterations can influence contraction.</p> Signup and view all the answers

    What is the molecular weight of the myosin complex approximately?

    <p>~500 kDa</p> Signup and view all the answers

    What activity does the myosin heads exhibit while binding ATP?

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

    Which type of muscle tissue is characterized by cross-striations and involuntary, rhythmic contractions?

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

    Where is smooth muscle typically found in the human body?

    <p>In the walls of hollow organs</p> Signup and view all the answers

    Which of the following statements correctly describes skeletal muscle?

    <p>It is controlled voluntarily and striated.</p> Signup and view all the answers

    What is the primary feature that distinguishes cardiac muscle from smooth muscle?

    <p>Presence of intercalated discs</p> Signup and view all the answers

    How do smooth muscles predominantly contract when compared to skeletal muscles?

    <p>They contract slowly and involuntarily.</p> Signup and view all the answers

    Which of the following best describes the organization of skeletal muscle tissue?

    <p>Elongated, striated cells that are multinucleated.</p> Signup and view all the answers

    What role does the sarcoplasmic reticulum play in muscle contraction?

    <p>Regulates calcium ion concentration for contraction.</p> Signup and view all the answers

    Which characteristic is NOT associated with smooth muscle tissue?

    <p>Presence of striations</p> Signup and view all the answers

    Study Notes

    Muscle Tissue Overview

    • Muscle tissue enables connection and movement of bones.
    • Three main types of muscle tissue: cardiac, skeletal, and smooth.

    Cardiac Muscle

    • Features cross-striations and branched cells.
    • Intercalated discs connect cells, allowing synchronous contraction.
    • Involuntary and rhythmic contraction.
    • Found exclusively in the heart.

    Skeletal Muscle

    • Organized into elongated muscle fibers.
    • Contains a sarcoplasmic reticulum and transverse tubular system for calcium ion transport.
    • Contraction mechanism involves cross-bridge cycling of thick (myosin) and thin (actin) filaments.
    • Innervated by motor neurons at the neuromuscular junction (NMJ).

    Mechanism of Contraction

    • Nerve impulses trigger acetylcholine release at NMJ.
    • Calcium ions released from the sarcoplasmic reticulum bind to troponin, exposing active sites on actin.
    • Myosin heads pivot to pull thin filaments toward the center of the sarcomere.
    • ATP powers the detach-and-return cycle, allowing repeated muscle contraction.

    Types of Skeletal Muscle Fibers

    • Type I: Slow oxidative fibers, maintain contractions over long periods without fatigue, primarily utilize aerobic respiration.
    • Type IIa: Fast oxidative-glycolytic fibers, designed for rapid short-term contractions, can switch energy sources.
    • Type IIb: Fast glycolytic fibers, primarily use anaerobic glycolysis, fatigue quickly.

    Smooth Muscle

    • Also known as visceral muscle, lacks striations.
    • Contains fusiform cells that contract slowly and involuntarily.
    • Present in walls of hollow organs like intestines and blood vessels.

    Cell Structure of Smooth Muscle

    • Cells exhibit uniform staining with a narrow part adjacent to broader sections of neighboring cells.
    • Linked by gap junctions, allowing coordinated contraction.
    • Contains organelles like mitochondria, ribosomes, and Golgi apparatus concentrated near the nucleus.
    • Includes caveolae, invaginations at the cell surface.

    Contracile Mechanism in Smooth Muscle

    • Dense bodies anchor intermediate and actin filaments, transmitting force during contraction.
    • Smooth muscle operates under autonomic control, influenced by hormones and local factors.
    • Lacks distinct motor end plates, instead relying on neurotransmitter diffusion across a synaptic cleft.

    Figure: Thick and Thin Filaments

    • Thick filaments (1.6 µm long, 15 nm wide) primarily composed of myosin.
    • Myosin structure includes heavy chains forming tails and light chains forming heads for ATP binding.
    • Cross-bridges formed between myosin heads and actin allow muscle contraction through energy release (actomyosin ATPase activity).

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    Description

    Explore the essential aspects of muscle tissue, including the three main types: cardiac, skeletal, and smooth muscle. This quiz covers their unique characteristics, mechanisms of contraction, and roles in the body. Test your knowledge on how muscle tissue enables movement and maintains bodily functions.

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