Smooth Muscle Physiology and Contraction
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Questions and Answers

How does smooth muscle contraction differ from skeletal muscle contraction in terms of its control?

  • Smooth muscle contraction is involuntary, controlled by the autonomic nervous system. (correct)
  • Smooth muscle contraction is involuntary, controlled by the somatic nervous system.
  • Smooth muscle contraction is voluntary, controlled by the somatic nervous system.
  • Smooth muscle contraction is voluntary, controlled by the autonomic nervous system.

    • How does the structure of smooth muscle differ from skeletal muscle?

  • Smooth muscle cells are multinucleated, while skeletal muscle cells are uninucleated.
  • Smooth muscle cells have a sarcomere arrangement, but skeletal muscle does not.
  • Smooth muscle has dense bodies, but skeletal muscle does not.
  • Smooth muscle lacks striations, but skeletal muscle does. (correct)

    • What is the primary role of dense bodies in smooth muscle?

  • To regulate calcium influx into the cell.
  • To produce ATP for muscle contraction.
  • To anchor actin filaments, similar to Z-discs in skeletal muscle. (correct)
  • To provide structural support for the cell.

    • Which of the following is NOT a feature of smooth muscle contraction?

    <p>Rapid and forceful contractions.</p> Signup and view all the answers

    What is the significance of the 'latch mechanism' in smooth muscle?

    <p>It maintains prolonged contractions with minimal energy expenditure.</p> Signup and view all the answers

    Which type of smooth muscle is characterized by synchronized contraction due to gap junctions between cells?

    <p>Single-unit (visceral) smooth muscle.</p> Signup and view all the answers

    What is an example of a structure where single-unit smooth muscle is found?

    <p>The intestines.</p> Signup and view all the answers

    Which of these are characteristics of tonic contractions?

    <p>They maintain constant tension, like regulating blood vessel pressure.</p> Signup and view all the answers

    What is the main function of smooth muscles in blood vessels?

    <p>Regulate blood pressure</p> Signup and view all the answers

    What initiates slow wave potentials in smooth muscle cells?

    <p>Interstitial cells of Cajal</p> Signup and view all the answers

    What is the resting membrane potential range for smooth muscle cells?

    <p>-50 mV to -60 mV</p> Signup and view all the answers

    Which of the following is NOT a typical phase of smooth muscle action potential formation?

    <p>Deactivation phase</p> Signup and view all the answers

    What increases muscle tension on slow wave potentials?

    <p>Spike potentials</p> Signup and view all the answers

    Which enzyme is primarily responsible for initiating contraction in smooth muscle?

    <p>Myosin Light Chain Kinase (MLCK)</p> Signup and view all the answers

    What type of smooth muscle action potential provides a baseline electrical rhythm?

    <p>Slow wave potentials</p> Signup and view all the answers

    What role does Myosin Light Chain Phosphatase (MLCP) play in smooth muscle function?

    <p>Dephosphorylates myosin, leading to relaxation</p> Signup and view all the answers

    What role does calcium play in smooth muscle action potential?

    <p>It directly changes membrane potential and activates enzymes.</p> Signup and view all the answers

    How does the duration of smooth muscle action potentials compare to those in skeletal muscles?

    <p>They are longer and more sustained.</p> Signup and view all the answers

    What is a characteristic of spontaneous activity in smooth muscles?

    <p>It can occur even without neural stimulation.</p> Signup and view all the answers

    Which of the following factors can trigger smooth muscle action potential?

    <p>Local changes in pH level.</p> Signup and view all the answers

    What is the function of MLCK in smooth muscle contraction?

    <p>To phosphorylate the regulatory light chains of myosin.</p> Signup and view all the answers

    In smooth muscle action, what initiates the opening of voltage-gated calcium channels?

    <p>An action potential or chemical signal.</p> Signup and view all the answers

    What is the primary difference between smooth muscle contraction and skeletal muscle contraction?

    <p>Smooth muscle uses the calcium-calmodulin-MLCK pathway instead of troponin-tropomyosin.</p> Signup and view all the answers

    What event follows the binding of calcium to calmodulin in smooth muscle contraction?

    <p>Calmodulin activates myosin light chain kinase (MLCK).</p> Signup and view all the answers

    Study Notes

    Smooth Muscle Physiology

    • Smooth muscle is involuntary, lacking striations (unlike skeletal muscle)
    • Found in internal organs (walls of organs)
    • Contractions are slow, sustained, and involuntary, controlled by the autonomic nervous system and hormonal mechanisms.
    • Smooth muscle cells are spindle-shaped, uninucleate, and lack sarcomeres
    • Microscopic Anatomy; Spindle-shaped cells, wider in the middle and tapered at the ends and contain a single nucleus centrally located.
    • Smooth muscle lacks striations. Actin and myosin filaments are arranged irregularly. Dense bodies anchor actin filaments; similar to the Z-discs of striated muscle.

    Smooth Muscle Contraction

    • Calcium-dependent: Calcium influx into the cell is essential for contraction. Contraction is triggered by myosin light chain kinase (MLCK) enzyme.
    • Contraction is slow but long-lasting and energy-efficient.
    • Smooth muscle contractions are triggered by neural, hormonal, or local factors. Neural stimulation, such as by the autonomic nervous system, is important.
    • Hormones, like oxytocin or adrenaline can cause contraction or relaxation.
    • Mechanical stretch also opens calcium channels
    • Local factors like changes in pH or increased carbon dioxide levels can influence the action potential.

    Types of Smooth Muscle

    • Single-unit (visceral) smooth muscle: Cells are connected by gap junctions, allowing synchronized contractions (found in the intestines and uterus).
    • Multi-unit smooth muscle: Cells contract independently and have finer control. (found in iris muscles, arrector pili muscles)

    Smooth Muscle Action Potentials

    • Smooth Muscle Action Potentials; Have slow potentials. Pacemaker cells in the intestines can generate spontaneous action potentials without neural simulation.
    • Two main types of smooth muscle action potentials; Slow-wave potentials and spike potentials.
    • Spike potentials; are rapid changes in the membrane potential similar to some other excitable cells (e.g., skeletal muscle, neurons).
    • Slow-wave potentials; are spontaneous fluctuations in the membrane potential not true action potentials; may trigger spike potentials which causes contraction.
    • Smooth muscle action potentials are slower and more prolonged than those in skeletal muscle and nerve cells

    Locations of Smooth Muscle

    • Blood vessel walls: Regulates blood pressure
    • Digestive system: Enables peristalsis (wave-like movements)
    • Respiratory tract: Controls bronchial diameter
    • Urogenital system: Controls contractions in the bladder, ureters, and uterus
    • Eye: Found in the iris and ciliary muscles

    Key Players in Smooth Muscle Contraction

    • Calcium: Triggers the contraction by activating calmodulin
    • Calmodulin (CaM): Binds calcium, activating MLCK
    • Myosin Light Chain Kinase (MLCK): Phosphorylates myosin enabling contraction
    • Myosin Light Chain Phosphatase (MLCP): Dephosphorylates myosin for relaxation

    Energy Requirement

    • Smooth muscle contraction requires very little energy (1/10 to 1/300 of skeletal muscle) due to fewer myosin filaments, lower myosin ATPase activity, and a lower rate of cross-bridge cycling
    • The latch mechanism of smooth muscle maintains prolonged contractions with minimal energy usage, by maintaining tension without active cycling.

    Smooth Muscle Action Potential Characteristics

    • Slow and Prolonged; A key characteristic is slow development and prolonged action potentials. The prolonged contraction process is energy-efficient

    Factors Triggering Smooth Muscle Action Potential

    • Neural Stimulation; from autonomic nervous system and hormones(Oxytocin and Adrenaline), Mechanical stretch, Local factors(Hypoxia)

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    Smooth Muscle Physiology PDF

    Description

    This quiz explores the unique characteristics of smooth muscle physiology and its contraction mechanisms. You'll learn about its involuntary nature, microscopic anatomy, and how contractions are regulated by various factors. Test your knowledge on the differences between smooth and striated muscle.

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