Physiology Exam 2 Chapter 12 Flashcards
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Questions and Answers

Which mechanism ensures a rapid and efficient removal of acetylcholine?

  • Acetylcholine is stored in vesicles.
  • Acetylcholine is transported into glial cells.
  • Acetylcholine is reabsorbed into axon terminals.
  • Acetylcholine is degraded by acetylcholinesterase. (correct)

    • Which statement describes a critical event that occurs at the neuromuscular junction?

  • ATP is hydrolyzed.
  • Calcium is released by the muscle fiber.
  • Acetylcholine is released by axon terminals of the motor neuron. (correct)
  • Myosin binds to actin.

    • These motor neurons __________.

    extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber.

    What triggers synaptic vesicles to release acetylcholine?

    <p>Calcium entry into the axon terminal.</p> Signup and view all the answers

    Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

    <p>the opening of ligand-gated cation channels.</p> Signup and view all the answers

    Why do sodium and potassium ions not diffuse in equal numbers through ligand-gated cation channels?

    <p>The inside surface of the sarcolemma is negatively charged compared to the outside surface.</p> Signup and view all the answers

    What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum?

    <p>arrival of an action potential.</p> Signup and view all the answers

    The binding of calcium to which molecule causes the myosin binding sites to be exposed?

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

    A myosin head binds to which molecule to form a cross bridge?

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

    What causes the myosin head to disconnect from actin?

    <p>binding of ATP.</p> Signup and view all the answers

    What causes the power stroke?

    <p>release of ADP and Pi.</p> Signup and view all the answers

    How is the opposite action (extension at the elbow) produced?

    <p>An antagonistic muscle produces the opposite movement.</p> Signup and view all the answers

    Which of the following is an effect of the parasympathetic nervous system?

    <p>airway constriction.</p> Signup and view all the answers

    What happens when calcium binds troponin?

    <p>Tropomyosin is pulled away from the actin's myosin-binding site.</p> Signup and view all the answers

    How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle?

    <p>It causes rotation of the myosin head, thus 'cocking' it.</p> Signup and view all the answers

    What is the function of transverse tubules?

    <p>rapidly conduct action potentials to the interior of the muscle fiber.</p> Signup and view all the answers

    What is the function of the titin protein?

    <p>stabilize the position of the contractile filaments.</p> Signup and view all the answers

    In order for high force crossbridges to form in contracting skeletal muscle, calcium must

    <p>bind to troponin which moves the tropomyosin.</p> Signup and view all the answers

    Each myosin head has a binding site for

    <p>actin and ATP.</p> Signup and view all the answers

    What happens as ATP binds to the myosin head at the beginning of a muscle contraction cycle?

    <p>The myosin head detaches from actin.</p> Signup and view all the answers

    What is the molecular event that occurs immediately after the power stroke?

    <p>release of ADP from the myosin.</p> Signup and view all the answers

    What does the hydrolysis of ATP cause myosin to do?

    <p>rotate into a position (cocked) to bind to actin.</p> Signup and view all the answers

    The action potential traveling along the T-tubule is detected by the

    <p>dihydropyridine (DHP) receptor (L-type calcium channel).</p> Signup and view all the answers

    What channel opens when acetylcholine binds to its receptor at the neuromuscular junction?

    <p>a channel for both Na+ and K+.</p> Signup and view all the answers

    The contraction cycle is triggered by the rise in ________ released from the sarcoplasmic reticulum (SR).

    <p>Ca2+.</p> Signup and view all the answers

    The brief period of time between the beginning of the action potential in the muscle and the beginning of contraction is referred to as the

    <p>latent period.</p> Signup and view all the answers

    ________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle.

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

    Which is a characteristic of slow-twitch oxidative skeletal muscle fibers?

    <p>Long contraction duration and high capillary density.</p> Signup and view all the answers

    A motor unit consists of

    <p>one neuron and all the skeletal muscle fibers it controls.</p> Signup and view all the answers

    Which fibers fatigue sooner?

    <p>fast-twitch fibers.</p> Signup and view all the answers

    Calcium, released by the sarcoplasmic reticulum, binds to ________ to move the ________, which allows actin to form a high-force crossbridge with myosin.

    <p>troponin C, tropomyosin.</p> Signup and view all the answers

    In order to contract and relax, muscle cells require energy in the form of ________. The immediate backup energy source is ________ that requires the enzyme ________.

    <p>ATP, phosphocreatine, creatine kinase.</p> Signup and view all the answers

    Asynchronous activation of motor units is important because it functions to prevent

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

    Smooth muscle cells lack which protein(s)?

    <p>troponin only.</p> Signup and view all the answers

    Which of the following is NOT a correct comparison of cardiac myocytes to other muscle cell types?

    <p>Contraction of cardiac muscle is under voluntary control.</p> Signup and view all the answers

    In smooth muscle cells, Ca2+ binds to ________ which activates the enzyme ________ to phosphorylate myosin and increase force.

    <p>calmodulin, myosin light chain kinase.</p> Signup and view all the answers

    In comparison to skeletal muscle, smooth muscle cells function over a ________ range of muscle lengths and exhibit a speed of contraction that is ________ than skeletal muscle.

    <p>wider, slower.</p> Signup and view all the answers

    What does excitation-contraction coupling refer to?

    <p>A series of events after impulses at the neuromuscular junction leading to muscle contraction.</p> Signup and view all the answers

    What specific event initiates the contraction of a skeletal muscle fiber?

    <p>Calcium release from the sarcoplasmic reticulum.</p> Signup and view all the answers

    How are components of a triad connected?

    <p>By a series of proteins that control calcium release.</p> Signup and view all the answers

    What name is given to the regularly spaced infoldings of the sarcolemma?

    <p>transverse or T tubules.</p> Signup and view all the answers

    Which is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

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

    What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

    <p>Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.</p> Signup and view all the answers

    What is a cross bridge?

    <p>A myosin head bound to actin.</p> Signup and view all the answers

    What structure is the functional unit of contraction in a skeletal muscle fiber?

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

    Where are calcium ions stored within the muscle fiber?

    <p>Calcium ions are stored in the sarcoplasmic reticulum.</p> Signup and view all the answers

    What causes cross bridge detachment?

    <p>ATP binds to the myosin head.</p> Signup and view all the answers

    How does the myosin head obtain the energy required for activation?

    <p>The energy comes from the hydrolysis of ATP.</p> Signup and view all the answers

    What specific event triggers the uncovering of the myosin binding site on actin?

    <p>Calcium ions bind to troponin and change its shape.</p> Signup and view all the answers

    When does cross bridge cycling end?

    <p>Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.</p> Signup and view all the answers

    In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

    <p>acetylcholine (ACh).</p> Signup and view all the answers

    When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

    <p>voltage-gated calcium channels.</p> Signup and view all the answers

    What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

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

    What occurs when the neurotransmitter binds to receptors on the motor end plate?

    <p>Chemically gated sodium channels open in the motor end plate.</p> Signup and view all the answers

    How is acetylcholine (ACh) removed from the synaptic cleft?

    <p>acetylcholinesterase (AChE; an enzyme).</p> Signup and view all the answers

    Where are calcium ions stored in the muscle cell?

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

    What role does calcium play in the cross bridge cycle?

    <p>Calcium binds to troponin, altering its shape.</p> Signup and view all the answers

    What role does tropomyosin play in the cross bridge cycle?

    <p>The displacement of tropomyosin exposes the active sites of actin.</p> Signup and view all the answers

    How does troponin facilitate cross bridge formation?

    <p>Troponin controls the position of tropomyosin on the thin filament.</p> Signup and view all the answers

    What, specifically, is a cross bridge?

    <p>myosin binding to actin.</p> Signup and view all the answers

    Which event causes cross bridge detachment?

    <p>ATP binding to the myosin head.</p> Signup and view all the answers

    Where in the cross bridge cycle does ATP hydrolysis occur?

    <p>during the cocking of the myosin head.</p> Signup and view all the answers

    How/when does the myosin head cock back to store energy for the next cycle?

    <p>After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.</p> Signup and view all the answers

    What effect would BMD have on the cross bridge cycle?

    <p>Myosin heads would remain detached, unable to cock.</p> Signup and view all the answers

    During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

    <p>There are always some myosin heads attached to actin.</p> Signup and view all the answers

    Which fibers generate more force?

    <p>fast-twitch fibers.</p> Signup and view all the answers

    Which ion signals the beginning of skeletal muscle contraction?

    <p>Ca2+.</p> Signup and view all the answers

    Slow-oxidative muscle fibers (type I) are characterized by the presence of myoglobin and

    <p>a smaller diameter and less stored glycogen.</p> Signup and view all the answers

    How does the process of smooth muscle contraction differ from contraction in skeletal muscle?

    <p>Ca2+ comes from the extracellular fluid as well as the SR.</p> Signup and view all the answers

    How are cardiac muscle cells similar to smooth muscle cells?

    <p>They are electrically linked to one another.</p> Signup and view all the answers

    Study Notes

    Action Potential and Acetylcholine

    • Action potential propagation ceases when acetylcholine (ACh) is removed from the synaptic cleft.
    • Acetylcholine is rapidly degraded by the enzyme acetylcholinesterase.

    Neuromuscular Junction Function

    • Critical event at the neuromuscular junction involves the release of acetylcholine from motor neuron axon terminals.
    • Action potentials travel from the brain or spinal cord to the sarcolemma of skeletal muscle fibers.

    Calcium and Muscle Contraction

    • Calcium entry into axon terminals triggers synaptic vesicles to release acetylcholine.
    • When ACh binds to receptors on the sarcolemma, ligand-gated cation channels open, allowing ion flow.
    • The arrival of an action potential causes calcium release from the terminal cisternae of the sarcoplasmic reticulum.
    • Calcium binds to troponin, exposing myosin-binding sites on actin.

    Myosin Functionality

    • Myosin heads bind to actin, forming cross bridges.
    • The binding of ATP to the myosin head causes it to detach from actin.
    • Power stroke is initiated by the release of ADP and inorganic phosphate (Pi) from the myosin head.
    • Myosin head's rotation (cocking) is powered by the hydrolysis of ATP.

    Muscle Structure and Function

    • Muscles move bones at joints; antagonistic muscles allow opposing movements.
    • Muscle cells utilize ATP for contraction and relaxation, with phosphocreatine serving as a rapid energy backup.

    Muscle Fiber Types

    • Slow-twitch oxidative fibers have long contraction durations and high capillary densities, while fast-twitch fibers fatigue sooner and generate more force.
    • Myosin heads require actin and ATP binding sites; asynchronous activation of motor units prevents fatigue.

    Smooth and Cardiac Muscle

    • Smooth muscle cells lack troponin and obtain Ca2+ from both extracellular fluid and the sarcoplasmic reticulum.
    • In cardiac muscle, contractions are under autonomic control, and cardiac cells are electrically linked.

    Cross Bridge Cycle

    • Calcium ions couple excitation of muscle fibers to contraction, stored in the sarcoplasmic reticulum.
    • Tropomyosin displacement exposes active sites on actin, facilitating cross bridge formation.
    • The cycle ends when calcium is actively transported back into the sarcoplasmic reticulum.

    Muscle Cell Activation and Control

    • Voltage-gated calcium channels open upon action potential arrival at the axon terminal.
    • Exocytosis is the method for releasing neurotransmitters into the synaptic cleft.

    Muscle Contraction Dynamics

    • Calcium ion binding to troponin alters its shape, allowing muscle contraction.
    • ATP binding to myosin is essential for cross bridge detachment, allowing continuous cycling.

    Summary of Muscle Conception

    • Each motor unit consists of one motor neuron and all muscle fibers it innervates.
    • The sarcomere serves as the functional unit of contraction, with muscle contractions triggered by calcium ion release from the sarcoplasmic reticulum.

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    Description

    This quiz focuses on key concepts from Chapter 12 of your Physiology exam. Explore critical events in neuromuscular junctions and the mechanisms behind action potential propagation in skeletal muscle fibers. Test your understanding and retention of essential physiological processes related to acetylcholine function.

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