Muscle and Muscle Tissue Study Quiz
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Questions and Answers

What is the primary function of acetylcholine (ACh) at the neuromuscular junction?

  • To provide energy for muscle contraction
  • To bind to receptors and initiate an action potential (correct)
  • To deactivate muscle fibers during relaxation
  • To enhance the release of neurotransmitters from the axon terminal

    • Which component of the neuromuscular junction acts as a barrier between the axon terminal and muscle fiber?

  • Motor end plate
  • Junctional folds
  • Synaptic vesicles
  • Synaptic cleft (correct)

    • What role does the enzyme acetylcholinesterase play at the neuromuscular junction?

  • To prevent excessive muscle contraction (correct)
  • To facilitate the entry of Ca2+ into the axon terminal
  • To enhance action potential propagation
  • To synthesise acetylcholine (ACh)

    • What initiates the release of acetylcholine from the synaptic vesicles in the axon terminal?

    <p>Action potential arrival and calcium ion influx (C)</p> Signup and view all the answers

    Where are acetylcholine (ACh) receptors primarily located?

    <p>In the junctional folds of the sarcolemma (B)</p> Signup and view all the answers

    What happens to acetylcholine after it binds to its receptor?

    <p>It undergoes immediate decay by acetylcholinesterase (C)</p> Signup and view all the answers

    What change occurs in the axon terminal when the action potential arrives?

    <p>Increased permeability leading to Ca2+ entry (A)</p> Signup and view all the answers

    The motor end plate is characterized by which feature?

    <p>It possesses junctional folds that increase receptor surface area (B)</p> Signup and view all the answers

    What role does calcium play in the muscle contraction process?

    <p>Calcium binds to troponin, exposing active sites on actin. (D)</p> Signup and view all the answers

    During excitation-contraction (E-C) coupling, where is calcium released from?

    <p>From the terminal cisternae of the sarcoplasmic reticulum. (D)</p> Signup and view all the answers

    What initiates the action potential that leads to muscle contraction?

    <p>A change in membrane potential propagated along the sarcolemma. (A)</p> Signup and view all the answers

    What occurs after calcium binds to troponin?

    <p>The active sites on actin are exposed for myosin binding. (B)</p> Signup and view all the answers

    Which of the following correctly sequences the steps of muscle contraction?

    <p>Action potential, calcium release, troponin and tropomyosin interaction. (A)</p> Signup and view all the answers

    What must occur for myosin to bind to actin during muscle contraction?

    <p>Calcium must bind to troponin and remove tropomyosin's blocking action (B)</p> Signup and view all the answers

    How do the T tubules contribute to muscle contraction?

    <p>They transmit the action potential deep into the muscle fiber. (A)</p> Signup and view all the answers

    What is the role of calcium ions during muscle contraction?

    <p>To bind to troponin and expose active sites on actin (C)</p> Signup and view all the answers

    What occurs during the power stroke phase of muscle contraction?

    <p>Myosin heads pull actin filaments toward the center of the sarcomere. (D)</p> Signup and view all the answers

    During excitation-contraction coupling, what is the first event that occurs?

    <p>Propagation of an action potential along the sarcolemma (B)</p> Signup and view all the answers

    What is the primary function of troponin in muscle contraction?

    <p>To block the actin active sites until calcium binds. (C)</p> Signup and view all the answers

    Which component blocks the active sites on actin prior to muscle contraction?

    <p>Tropomyosin (A)</p> Signup and view all the answers

    What triggers the release of calcium ions from the sarcoplasmic reticulum?

    <p>Voltage-sensitive tubule proteins detection (A)</p> Signup and view all the answers

    Which of the following best describes the role of myosin in muscle contraction?

    <p>Myosin forms cross bridges with actin during contraction (C)</p> Signup and view all the answers

    What is the final outcome of calcium binding to troponin?

    <p>Active sites on actin are exposed for myosin binding (A)</p> Signup and view all the answers

    What action occurs after calcium is released from the sarcoplasmic reticulum?

    <p>Active sites on actin are exposed (C)</p> Signup and view all the answers

    What initiates the generation of the end plate potential on the sarcolemma?

    <p>ACh binds to receptors causing Na+ influx. (A)</p> Signup and view all the answers

    During the propagation of the action potential, what occurs immediately after local depolarization?

    <p>Repolarization of the membrane begins. (B)</p> Signup and view all the answers

    What role do Na+ channels play in the generation of the action potential?

    <p>They open to allow Na+ influx into the muscle fiber. (A)</p> Signup and view all the answers

    What occurs during the repolarization phase of the action potential?

    <p>K+ ions flow out of the cell, restoring the negative membrane potential. (D)</p> Signup and view all the answers

    How does local depolarization affect the Na+ and K+ channels at the axon terminal?

    <p>Open Na+ channels lead to Na+ influx, while K+ channels remain closed. (B)</p> Signup and view all the answers

    What is the role of ACh in the synaptic cleft during action potential generation?

    <p>It binds to receptors, triggering the opening of Na+ channels. (B)</p> Signup and view all the answers

    Which of the following statements is true regarding the action potential sequence?

    <p>The action potential cannot be propagated without voltage-gated K+ channels. (C)</p> Signup and view all the answers

    What mechanism is responsible for restoring the resting membrane potential after an action potential?

    <p>Inactivation of Na+ channels and opening of K+ channels. (D)</p> Signup and view all the answers

    What characterizes isometric muscle contraction?

    <p>Muscle length remains unchanged with tension produced. (C)</p> Signup and view all the answers

    Which type of skeletal muscle fiber is primarily resistant to fatigue?

    <p>Intermediate fibers resembling fast fibers. (C)</p> Signup and view all the answers

    Which statement is true regarding smooth muscle contraction?

    <p>Calmodulin plays a key role in regulating smooth muscle contraction. (D)</p> Signup and view all the answers

    What structural characteristic distinguishes skeletal muscle fibers from smooth muscle fibers?

    <p>Skeletal muscle fibers have striations and sarcomeres. (B)</p> Signup and view all the answers

    Which neurotransmitters are known to affect smooth muscle?

    <p>Acetylcholine and norepinephrine (C)</p> Signup and view all the answers

    What is a notable difference between slow and fast skeletal muscle fibers?

    <p>Fast fibers contain more mitochondria for energy production. (D)</p> Signup and view all the answers

    Which characteristic is NOT associated with smooth muscle?

    <p>Involuntary and requires conscious control. (C)</p> Signup and view all the answers

    What describes the vascular role of smooth muscle?

    <p>It helps regulate blood vessel diameter and blood flow. (D)</p> Signup and view all the answers

    What is the role of calcium ions (Ca2+) in muscle contraction?

    <p>Calcium binds to troponin, causing tropomyosin to move and expose active sites. (D)</p> Signup and view all the answers

    What happens to muscle fibers when intracellular Ca2+ concentration is low?

    <p>Tropomyosin blocks the active sites on actin. (B)</p> Signup and view all the answers

    During the cross bridge cycle, what is the significance of ATP hydrolysis?

    <p>It provides energy for myosin head cocking into a high-energy state. (D)</p> Signup and view all the answers

    What initiates the end of muscle contraction?

    <p>Pump back of Ca2+ into the sarcoplasmic reticulum. (C)</p> Signup and view all the answers

    What correctly describes the 'working stroke' of the cross bridge cycle?

    <p>The myosin head pivots and pulls the thin filament toward the M line. (A)</p> Signup and view all the answers

    What is the correct sequence of events in the cross bridge cycle?

    <p>Cross bridge formation, power stroke, detachment, cocking. (D)</p> Signup and view all the answers

    How does the binding of ATP affect the myosin head?

    <p>It causes the myosin head to fall off actin. (C)</p> Signup and view all the answers

    What activates the contraction process in muscle fibers?

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    What happens to myosin heads at low intracellular Ca2+ concentrations?

    <p>Myosin heads cannot bind to actin. (A)</p> Signup and view all the answers

    During the cross bridge cycle, what role does ATP play immediately after the power stroke?

    <p>It facilitates cross bridge detachment. (D)</p> Signup and view all the answers

    What initiates the process that leads to muscle contraction following an increase in intracellular Ca2+ levels?

    <p>Troponin changes shape. (B)</p> Signup and view all the answers

    Which statement accurately describes the cocking of the myosin head?

    <p>Hydrolysis of ATP cocks the myosin head into a high-energy state. (B)</p> Signup and view all the answers

    What occurs when nervous stimulation ceases in muscle fibers?

    <p>Calcium is pumped back into the sarcoplasmic reticulum. (C)</p> Signup and view all the answers

    What is the function of tropomyosin during the resting state of muscle fibers?

    <p>It blocks the active sites on actin. (D)</p> Signup and view all the answers

    Which component is essential for maintaining the cross bridge cycle in muscle contraction?

    <p>Adequate ATP (B)</p> Signup and view all the answers

    In muscle contraction, what is the result of myosin heads attaching to actin?

    <p>Cross bridge formation occurs. (D)</p> Signup and view all the answers

    Flashcards

    Neuromuscular Junction

    The connection between a motor neuron and a muscle fiber.

    Synaptic Knob

    The expanded end of the motor neuron axon at the neuromuscular junction.

    Synaptic Vesicles

    Sacs in the synaptic knob containing acetylcholine (ACh).

    Acetylcholine (ACh)

    Neurotransmitter that triggers muscle contraction.

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    Motor End Plate

    Specialized region of the muscle fiber membrane involved in ACh reception.

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    Acetylcholinesterase

    Enzyme that breaks down ACh, ending the signal.

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    Synaptic Cleft

    The space between the motor neuron and muscle fiber.

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    Action Potential (AP)

    Electrical signal that travels along a nerve.

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    Action potential

    A rapid change in the electrical potential across a nerve cell membrane, transmitting signals.

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    Neurotransmitter release

    The process of releasing neurotransmitters across the synaptic cleft to communicate with other nerve cells.

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    End plate potential

    The initial depolarization of the muscle fiber membrane in response to a nerve impulse.

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    Depolarization

    Increase in the membrane potential.

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    Repolarization

    Return to the resting membrane potential following depolarization.

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    Sarcolemma

    The muscle cell membrane.

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    Sarcoplasm

    The cytoplasm of a muscle cell.

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    T Tubules

    Invaginations of the sarcolemma that extend deep into the muscle fiber, carrying action potentials.

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    Terminal Cisterna

    Expanded ends of the sarcoplasmic reticulum (SR) that lie close to T tubules.

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    Ca2+ Release Channel

    A protein in the terminal cisterna that releases calcium ions into the sarcoplasm in response to an action potential.

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    Troponin

    A protein on actin that binds to calcium, initiating muscle contraction.

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    Tropomyosin

    A protein that blocks the myosin-binding sites on actin when a muscle is relaxed.

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    Myosin Binding Sites

    Locations on actin where myosin heads can attach and pull during contraction.

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    Myosin Cross-Bridge

    The connection between a myosin head and an actin filament during muscle contraction.

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    Active Sites

    Specific regions on actin where myosin heads can bind and interact, initiating muscle contraction.

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    Cross Bridge Formation

    The process where a myosin head attaches to an active site on actin, forming a connection that initiates the contraction cycle.

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    Power Stroke

    The movement of the myosin head pulling the thin filament towards the M line, shortening the sarcomere and generating muscle contraction.

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    Cross Bridge Detachment

    The release of the myosin head from the active site, facilitated by ATP binding, allowing the cycle to repeat.

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    Cocking of Myosin Head

    The process where myosin heads are re-energized to their high-energy state using energy from ATP hydrolysis, preparing for another power stroke.

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    Role of Calcium in Contraction

    Calcium ions (Ca2+) play a crucial role in muscle contraction by binding to troponin, uncovering the active sites on actin and enabling the myosin-actin interactions that drive muscle contraction.

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    What is the role of calcium in muscle contraction?

    Calcium ions (Ca2+) bind to troponin, causing it to move tropomyosin away from the myosin-binding sites on actin. This uncovers the active sites, allowing myosin to bind to actin and initiate the contraction cycle.

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    What triggers the release of calcium ions inside a muscle cell?

    An action potential traveling down the T tubule triggers the release of calcium ions from the sarcoplasmic reticulum (SR).

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    Sarcoplasmic Reticulum (SR)

    A network of intracellular membranes that stores calcium ions. When an action potential arrives, the SR releases these calcium ions into the sarcoplasm, triggering muscle contraction.

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    How is muscle contraction terminated?

    Muscle contraction is terminated by the removal of calcium ions from the sarcoplasm. The SR actively pumps calcium back inside, returning tropomyosin to its blocking position and preventing myosin from binding to actin.

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    What are the main steps of excitation-contraction (E-C) coupling?

    E-C coupling is the process of converting an electrical signal (action potential) into a mechanical response (muscle contraction).

    1. Action Potential: An action potential travels down the sarcolemma and down the T tubules
    2. Calcium Release: Calcium ions are released from the sarcoplasmic reticulum (SR)
    3. Binding: Calcium ions bind to troponin, causing it to move tropomyosin away from the myosin-binding sites on actin.
    4. Contraction: Myosin binds to actin and initiates the contraction cycle, causing the muscle to shorten.
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    Isometric Contraction

    Muscle tension increases, but the muscle length stays the same. The force generated is not enough to overcome the resistance.

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    Isotonic Contraction

    Muscle tension overcomes resistance, causing the muscle to shorten and movement to occur.

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    Fast Muscle Fibers

    Large, powerful fibers that contract quickly but fatigue easily. They have low myoglobin content.

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    Slow Muscle Fibers

    Smaller, slower contracting fibers that are resistant to fatigue. They have high myoglobin content.

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    Smooth Muscle

    Involuntary muscle found in internal organs, vessels, and the eye. It contracts slowly and has no striations.

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    Calmodulin

    A protein that binds calcium ions in smooth muscle cells, triggering contraction.

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    Differences Between Skeletal & Smooth Muscle

    Smooth muscle lacks troponin and relies on calmodulin for contraction. It is also affected by hormones and stretching.

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    Dense Bodies

    Points within smooth muscle cells where thin filaments attach, similar to Z discs in skeletal muscle.

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    Study Notes

    Muscle and Muscle Tissue

    • Muscle tissue is responsible for movement in the body.
    • There are three main types of muscle tissue: skeletal, smooth, and cardiac.
    • Objectives for the study of muscle and muscle tissue include understanding the requirements for skeletal muscle contraction, neuromuscular junction events, action potential generation, excitation-contraction coupling, smooth muscle anatomy and physiology, and more.

    Requirements for Skeletal Muscle Contraction

    • Activation involves neural stimulation at the neuromuscular junction.
    • Excitation-contraction coupling involves the generation and propagation of an action potential along the sarcolemma.
    • The trigger for contraction is a rise in intracellular calcium (Ca²⁺) levels.

    Events at the Neuromuscular Junction

    • Skeletal muscles are stimulated by somatic motor neurons.
    • Motor neuron axons travel to skeletal muscles via nerves.
    • Each axon branches to form neuromuscular junctions with individual muscle fibers.
    • Axon endings form neuromuscular junctions.

    Action Potential at the Neuromuscular Junction

    • Action potentials arrive at the axon terminal of a motor neuron.
    • Voltage-gated calcium channels open, allowing calcium to enter the axon terminal.
    • Calcium entry triggers synaptic vesicles to release acetylcholine.
    • Acetylcholine diffuses across the synaptic cleft and binds to receptors on the sarcolemma.
    • Acetylcholine binding opens ion channels in the sarcolemma allowing the simultaneous passage of sodium into and potassium out of the muscle fibre.

    Destruction of Acetylcholine

    • Acetylcholine effects are terminated by the enzyme acetylcholinesterase.
    • This prevents continued muscle contraction in the absence of stimulation.

    Events in Generation of an Action Potential

    • Local Depolarization (End Plate Potential):
      • Acetylcholine binding opens chemically-gated ion channels.
      • Simultaneous diffusion of sodium (inward) and potassium (outward) occurs.
      • A rise in sodium ions makes the interior of the sarcolemma less negative, causing depolarization.
    • Generation and Propagation of Action Potential:
      • This end plate potential spreads to adjacent areas of the membrane.
      • Voltage-gated sodium channels open.
      • The influx of sodium decreases membrane potential toward a critical threshold.
    • If threshold is reached: An action potential is generated.
    • Repolarization:
      • Sodium channels close and voltage-gated potassium channels open.
      • Potassium efflux rapidly restores resting membrane potential.
      • The muscle fiber is in a refractory period until repolarization is complete.

    Excitation-Contraction (E-C) Coupling

    • This describes the events converting an action potential into muscle contraction.
    • The action potential propagates along the sarcolemma to T-tubules.
    • Voltage-sensitive proteins stimulate calcium release from the sarcoplasmic reticulum (SR).
    • Calcium is essential to muscle contraction.

    Mechanism of Contraction

    • Calcium binds to troponin.
    • Troponin conformation changes, exposing the myosin-binding sites on actin.
    • Myosin binds to actin.
    • ATP cleavage causes myosin to bend, pulling the actin filament.
    • A new ATP binds, detaching the myosin head.
    • The myosin head then recocks, ready for the next cycle.

    Role of Calcium (Ca²⁺) in Contraction

    • At low intracellular Ca²⁺ concentrations, tropomyosin blocks actin-binding sites, myosin heads cannot attach, and the muscle relaxes.
    • At high concentrations, Ca²⁺ binds to troponin, moving tropomyosin away and allowing myosin binding and the cross-bridge cycle.
    • When nervous stimulation ceases, Ca²⁺ is pumped back into SR, stopping contraction.

    The Cross-Bridge Cycle

    • The cycle continues as long as there is both calcium signal and ATP.
    • Cross-bridge formation: energized myosin head attaches to actin filament.
    • Power stroke: myosin head pivots, pulls thin filament towards M line.
    • Cross-bridge detachment: ATP attaches, causing myosin to detach.
    • "Cocking" of myosin head: ATP hydrolysis recocks myosin head.

    Some Sites Showing Animations of Muscle Contraction

    • Sites showing animations of muscle contraction for further study are provided.

    All-or-None Principle

    • A single muscle fiber either contracts completely or not at all.
    • A motor unit contracts all fibers simultaneously.
    • Total muscle force depends on the number of activated motor units.

    Contraction Types

    • Isometric: Muscle tension is generated, but not enough to overcome resistance, thus no change in muscle length.
    • Isotonic: Muscle tension exceeds resistance, leading to muscle shortening and movement.

    Three Types of Skeletal Muscle Fibers

    • Fast fibers: Large diameter, high glycogen reserves, densely packed myofibrils, relatively few mitochondria, fast contractions, white in color, and fatigue quickly.
    • Intermediate fibers: Resemble fast fibers but have greater fatigue resistance.
    • Slow fibers: Smaller diameter, low glycogen reserves, more mitochondria, slow contractions, red in color, and resist fatigue.

    Smooth Muscle

    • Found in internal organs, arteries, veins, and iris of the eye.
    • Involuntary function (without conscious thought or control).
    • Contractions to cause movement in these systems.
    • Contraction mechanisms are different from skeletal muscle, lacking troponin and using calmodulin and phosphorylation of myosin light chain kinase.
    • Slower to contract and relax, more resistant to fatigue.

    Muscle Atrophy

    • Reduction in muscle size, tone, and power.
    • Due to reduced stimulation.
    • Muscle becomes flaccid losing mass & tone, fibers decrease in size and become weak.
    • Even temporary reduction in muscle use can cause atrophy.

    Muscle Hypertrophy

    • An increase in muscle fiber size.
    • Muscle size can be improved through exercise.
    • Repetitive exhaustive stimulation increases mitochondria, glycogen reserves, and ability to produce ATP.
    • Each fiber develops more myofibrils, with each myofibril containing a greater number of myofilaments.

    Rigor Mortis

    • Stiffening of the body after death, beginning 3-4 hours postmortem.
    • Calcium activates myosin-actin cross-bridging, causing muscle contraction, but ATP production stops, thus muscle cannot relax.
    • Myofilaments remain locked until they decay.

    Identifying Muscle Types

    • Images showing cardiac, smooth, and skeletal muscles are provided.

    Practice Questions

    • The basic functional unit of skeletal muscle tissue is the sarcomere.
    • Calcium is essential for muscle contraction.
    • Smooth muscles control the flow of substances in the body's organs.
    • Tendons connect bone to muscle..
    • Sesamoid is not a type of muscle tissue.

    References

    • The provided references contain additional information about the topic.

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    Description

    Test your knowledge on muscle tissue and its functions. This quiz covers the types of muscle tissue, the process of skeletal muscle contraction, and events at the neuromuscular junction. Review important concepts and ensure you understand the physiological mechanisms that enable movement in the body.

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