Smooth Muscle Overview and Types
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Smooth Muscle Overview and Types

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Questions and Answers

What is a primary characteristic of smooth muscle that distinguishes it from skeletal and cardiac muscle?

  • Involuntary control (correct)
  • Containment of large cells (correct)
  • Presence of multiple nuclei (correct)
  • Presence of striations

    • Which system controls smooth muscle tissue?

  • Voluntary nervous system
  • Somatic nervous system
  • Autonomic nervous system (correct)
  • Central nervous system

    • What is the role of calcium ions in smooth muscle function?

  • To strengthen muscle fibers
  • To create striations
  • To trigger cross-bridge activity (correct)
  • To increase voluntary control

    • Where is smooth muscle primarily located?

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

    How does smooth muscle generate force?

    <p>By cross-bridge movements between actin and myosin</p> Signup and view all the answers

    What characterizes multi-unit smooth muscle?

    <p>Each fiber operates independently and is often innervated by a single nerve fiber.</p> Signup and view all the answers

    What is the purpose of the basement membrane in multi-unit smooth muscle?

    <p>To provide insulation between separate muscle fibers.</p> Signup and view all the answers

    How do multi-unit smooth muscle fibers compare to skeletal muscle fibers?

    <p>They operate independently similar to skeletal muscle fibers.</p> Signup and view all the answers

    Which of the following is true about unitary smooth muscle?

    <p>It often functions as a single unit due to linked fibers.</p> Signup and view all the answers

    Which type of smooth muscle is characterized by individual fibers that operate independently?

    <p>Multi-unit smooth muscle</p> Signup and view all the answers

    In the diagram of smooth muscle types, how is multi-unit smooth muscle depicted?

    <p>As separate fibers with autonomic neurons.</p> Signup and view all the answers

    What is a key feature of multi-unit smooth muscle regarding nerve innervation?

    <p>Each fiber is innervated by a single nerve ending</p> Signup and view all the answers

    What substance covers the outer surfaces of multi-unit smooth muscle fibers?

    <p>Basement membrane-like substance</p> Signup and view all the answers

    Which of the following is NOT a characteristic of multi-unit smooth muscle?

    <p>Fibers are continuously contracting</p> Signup and view all the answers

    Which of these statements is true about the composition of multi-unit smooth muscle?

    <p>It consists of separate smooth muscle fibers</p> Signup and view all the answers

    What is a primary characteristic of multi-unit smooth muscle?

    <p>Each fiber contracts independently of the others.</p> Signup and view all the answers

    Which type of smooth muscle is controlled by non-nervous stimuli?

    <p>Unitary smooth muscle</p> Signup and view all the answers

    Which structure is NOT associated with multi-unit smooth muscle?

    <p>Communicating gap junctions</p> Signup and view all the answers

    What allows for synchronized contraction in unitary smooth muscle?

    <p>Gap junctions between adjacent cells</p> Signup and view all the answers

    How do multi-unit and unitary smooth muscle primarily differ?

    <p>In the independence of fiber contractions</p> Signup and view all the answers

    What does the term 'unitary' refer to in unitary smooth muscle?

    <p>It indicates a mass of smooth muscle fibers contracting together as a unit.</p> Signup and view all the answers

    How are the cell membranes of unitary smooth muscle fibers connected?

    <p>They are adherent at multiple points.</p> Signup and view all the answers

    What is a key feature of unitary smooth muscle that allows coordinated contraction?

    <p>Many gap junctions facilitating ion flow.</p> Signup and view all the answers

    Where is unitary smooth muscle primarily found in the body?

    <p>In the walls of various viscera.</p> Signup and view all the answers

    What initiates a contractile response in unitary smooth muscles?

    <p>Stretching of the muscle</p> Signup and view all the answers

    What is another name for unitary smooth muscle?

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

    What characteristic differentiates smooth muscle contraction from skeletal muscle contraction?

    <p>Smooth muscle contracts in response to stretching</p> Signup and view all the answers

    Where are the thin filaments of smooth muscle anchored?

    <p>To dense bodies or the plasma membrane</p> Signup and view all the answers

    Which of the following components is absent in smooth muscle compared to skeletal muscle?

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

    What is functionally similar to the Z lines in skeletal muscle fibers within smooth muscle?

    <p>Dense bodies</p> Signup and view all the answers

    What happens to smooth muscle fibers during the contracted state?

    <p>They become shorter and thicker.</p> Signup and view all the answers

    Which component is necessary for triggering the contraction of smooth muscle?

    <p>Calcium ions</p> Signup and view all the answers

    What is ATP broken down into during smooth muscle contraction?

    <p>Adenosine diphosphate</p> Signup and view all the answers

    What structure acts as the outer membrane of a smooth muscle cell?

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

    Which filaments are involved in the contractile process of smooth muscle?

    <p>Actin and myosin filaments</p> Signup and view all the answers

    What factor most significantly determines the shortening velocity of smooth muscle compared to skeletal muscle?

    <p>The rate of ATP hydrolysis</p> Signup and view all the answers

    What is the effect of the low ATPase activity of smooth muscle myosin?

    <p>Increases the fatigue resistance of smooth muscle</p> Signup and view all the answers

    Which process enables myosin to bind to actin in smooth muscle contraction?

    <p>Phosphorylation of myosin by myosin kinase</p> Signup and view all the answers

    What role does calmodulin play in smooth muscle contraction?

    <p>It activates myosin kinase upon binding to calcium</p> Signup and view all the answers

    Which of the following statements best describes the rate of smooth muscle contraction compared to skeletal muscle?

    <p>Smooth muscle contraction is slower due to lower ATP hydrolysis rates</p> Signup and view all the answers

    What is the first step that occurs after an increase in cytosolic Ca2+ in smooth muscle fibers?

    <p>Ca2+ binds to calmodulin</p> Signup and view all the answers

    What role does myosin light-chain kinase play in smooth muscle contraction?

    <p>It phosphorylates myosin light chains</p> Signup and view all the answers

    What happens to the cross-bridge when myosin light chains are phosphorylated?

    <p>It binds to actin</p> Signup and view all the answers

    How do the changes mediated by Ca2+ in smooth muscle differ from those in striated muscle?

    <p>Ca2+ activates the thick filaments in smooth muscle</p> Signup and view all the answers

    What is required for cross-bridges to continue generating force in smooth muscle?

    <p>Phosphorylation of myosin light chains</p> Signup and view all the answers

    What is the primary regulatory mechanism for smooth muscle contraction?

    <p>Calmodulin activation of myosin light-chain kinase</p> Signup and view all the answers

    What initiates the phosphorylation of myosin in smooth muscle?

    <p>Calcium binding to calmodulin</p> Signup and view all the answers

    Which protein is absent in smooth muscle that is present in skeletal muscle?

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

    Which statement accurately describes the cross-bridge cycling process in smooth muscle?

    <p>It requires phosphorylated myosin to bind to actin</p> Signup and view all the answers

    What is the first step in the mechanism of smooth muscle contraction?

    <p>Formation of the calmodulin-calcium complex</p> Signup and view all the answers

    Study Notes

    Smooth Muscle: Overview

    • Smooth muscle is a type of muscle tissue responsible for involuntary movements in the body. It lacks striations present in skeletal and cardiac muscle.
    • Smooth muscle is innervated by the autonomic nervous system and is not under voluntary control.
    • Smooth muscle contraction relies on cross-bridge movements between actin and myosin filaments, which are regulated by calcium ions.

    Types of Smooth Muscle

    • Multi-unit smooth muscle: Composed of independent fibers, each controlled by a single nerve ending.
      • Examples: ciliary muscle of the eye, iris muscle of the eye
    • Unitary (single-unit) smooth muscle: A mass of connected fibers that contract as a single unit.
      • Found in walls of visceral organs, like the gastrointestinal tract, blood vessels, and uterus
      • Characterized by gap junctions that allow for synchronized contraction.

    Smooth Muscle Contraction and Control

    • Smooth muscle contraction differs from skeletal muscle in the mechanism of calcium binding and myosin activation.
      • Smooth muscle lacks troponin: Calcium binds to calmodulin, which activates myosin light-chain kinase (MLCK).
      • MLCK phosphorylates myosin: Phosphorylated myosin can then bind to actin and undergo cross-bridge cycling.
    • Smooth muscle myosin has a slow rate of ATPase activity: This results in slower contraction and reduced fatigue compared to skeletal muscle.

    Unique Features of Smooth Muscle

    • Stretch-induced contraction: Some smooth muscles can contract in response to stretching, like the stomach wall.
    • Dense bodies: These structures are functionally similar to Z-lines in skeletal muscle and anchor thin filaments.

    Diagram Interpretation

    • The provided diagram illustrates the steps involved in smooth muscle contraction.
    • It highlights the roles of calcium, calmodulin, myosin kinase, ATP, actin, and myosin in the process.
    • The diagram depicts the transition of the smooth muscle fiber from a relaxed state to a contracted state, emphasizing the shortening and thickening of the fiber.
    • Labels on the diagram identify key structures and components, including the sarcolemma, dense bodies, intermediate filaments, nucleus, thick filaments, and thin filaments.

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    Description

    This quiz covers the fundamental aspects of smooth muscle, including its characteristics, types, and contraction mechanisms. Learn the differences between multi-unit and unitary smooth muscle, and understand their functions in various organs of the body.

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