Neuroscience Membrane Potential
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Questions and Answers

What is the process called when multiple subthreshold potentials are added together to reach the threshold for an action potential?

  • Spatial Summation
  • Temporal Summation (correct)
  • Repolarization
  • Hyperpolarization

    • During the depolarization stage of an action potential, which gates open quickly?

  • K+ activation gates
  • Na+ activation gates (correct)
  • Ca2+ activation gates
  • K+ inactivation gates

    • What occurs once the sodium inactivation gates are closed?

  • Hyperpolarization is eliminated.
  • An action potential can be generated immediately.
  • The membrane depolarizes further.
  • The membrane returns to resting potential. (correct)

    • Which phase involves the membrane potential becoming more negative as potassium ions rush out of the cell?

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

    What is the resting membrane potential typically measured at?

    <p>-70 to -90 mV</p> Signup and view all the answers

    What defines the absolute refractory period?

    <p>No action potential can be generated at all.</p> Signup and view all the answers

    Which statement is true regarding the inactivation gates of Na+ during an action potential?

    <p>They are closed at the peak of the action potential.</p> Signup and view all the answers

    What change occurs during the relative refractory period?

    <p>A stronger than usual stimulus can generate an action potential.</p> Signup and view all the answers

    What occurs during the hyperpolarization phase?

    <p>K+ activation gates are slow to close.</p> Signup and view all the answers

    How does accommodation affect the membrane?

    <p>The membrane is held in a hypo-polarized state.</p> Signup and view all the answers

    Which type of summation occurs when two or more presynaptic inputs arrive simultaneously from multiple sources?

    <p>Spatial Summation</p> Signup and view all the answers

    What is the main factor that increases action potential conduction velocity?

    <p>Myelination of the nerve fibers.</p> Signup and view all the answers

    What initiates an action potential in the axon hillock?

    <p>Depolarization reaching a threshold level.</p> Signup and view all the answers

    At the peak of the action potential, which of the following is true of the K+ activation gates?

    <p>They are just beginning to open.</p> Signup and view all the answers

    What happens to the sodium channels during the action potential phase?

    <p>Sodium channels open and allow sodium to flow into the cell.</p> Signup and view all the answers

    What is the role of the nodes of Ranvier in nerve conduction?

    <p>They facilitate the jumping of action potentials between nodes.</p> Signup and view all the answers

    What characteristic best describes skeletal muscle cells?

    <p>Voluntary, striated, and multinucleated</p> Signup and view all the answers

    What is the primary role of nebulin in skeletal muscle?

    <p>Holds actin filaments in place</p> Signup and view all the answers

    Which protein serves as the structural anchor for thick myosin filaments?

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

    What defines a sarcomere in muscle tissue?

    <p>The functional unit bounded by two Z discs</p> Signup and view all the answers

    What is primarily contained in the H zone of a sarcomere?

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

    Which component of skeletal muscle is responsible for regulatory functions during contraction?

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

    What characterizes the A band in skeletal muscle?

    <p>Stays the same length during contraction</p> Signup and view all the answers

    What distinguishes the M line in a sarcomere?

    <p>Holds thick myosin filaments in place</p> Signup and view all the answers

    What is the primary structural protein that makes up the I line boundary between sarcomeres?

    <p>α-actinin</p> Signup and view all the answers

    Which ion is released by the sarcoplasmic reticulum to trigger muscle contraction?

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

    What role does troponin play in muscle contraction?

    <p>It inhibits the interaction of actin and myosin.</p> Signup and view all the answers

    What happens when calcium ions bind to troponin?

    <p>It moves tropomyosin away, exposing binding sites on actin.</p> Signup and view all the answers

    What is the result of the cross bridge cycle during muscle contraction?

    <p>Myosin binds to actin and causes the actin filaments to slide past.</p> Signup and view all the answers

    What role does ATP play in muscle contraction?

    <p>It hydrolyzes to provide energy for myosin heads.</p> Signup and view all the answers

    What is the function of the sarcolemma in muscle contraction?

    <p>To initiate an action potential.</p> Signup and view all the answers

    In a sarcomere, what structural feature is responsible for the light band appearance?

    <p>Thin filaments</p> Signup and view all the answers

    What is a characteristic of fast twitch fibers?

    <p>Greater strength of contraction due to large size</p> Signup and view all the answers

    Which process is primarily responsible for energy release in fast twitch fibers?

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

    What is the definition of isometric contraction?

    <p>Muscle length does not change but tension increases</p> Signup and view all the answers

    Which type of muscle contraction occurs when the muscle lengthens?

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

    What mainly regulates chemical synapses?

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

    What is a defining characteristic of the synaptic delay in chemical synapses?

    <p>Takes longer than electrical transmission</p> Signup and view all the answers

    What is true about motor units with fine motor control?

    <p>They consist of fewer muscle fibers per motor neuron</p> Signup and view all the answers

    Which type of signaling allows for simultaneous contraction of cardiac muscle?

    <p>Electrical signaling through gap junctions</p> Signup and view all the answers

    Study Notes

    Summation and Action Potential Generation

    • Summation: The process of adding multiple subthreshold potentials to reach the threshold and generate an action potential.
    • Temporal Summation: Involves two or more presynaptic inputs arriving at the same postsynaptic cell in quick succession from a single source.
    • Spatial Summation: Occurs when two or more presynaptic inputs arrive at a postsynaptic cell simultaneously from multiple sources.

    Action Potential Sequence

    • Polarized State: The resting membrane potential ranges from -70 to -90 mV; Na+ activation and inactivation gates are closed while K+ activation gates are also initially closed.
    • Depolarization Stage: Threshold is reached, leading to:
      • Rapid opening of Na+ activation gates.
      • Full closure of Na+ inactivation gates at peak.
      • Slow closure of K+ activation gates and slow opening of K+ channels.
      • Na+ influx results in a more positive membrane potential.
    • Repolarization Phase: After reaching the peak of the action potential:
      • Na+ inactivation gates are closed while K+ activation gates are open.
      • Na+ flow into the cell ceases, and K+ exits, making the membrane potential more negative.
    • Hyperpolarization:
      • K+ activation gates are slow to close, causing the membrane potential to drop below the resting level.
      • Membrane returns to resting potential once gates close.

    Refractory Periods

    • Absolute Refractory Period: No action potential can be generated because Na+ inactivation gates are closed.
    • Relative Refractory Period: An action potential can be generated with a greater than usual stimulus, corresponding with the hyperpolarization phase.

    Accommodation

    • A hypo-polarized state where the membrane cannot return to resting potential.
    • Na+ inactivation gates remain closed, preventing further action potential generation.

    Action Potential Propagation

    • Initiated at the axon hillock when depolarization occurs.
      • Local currents spread to adjacent inactive regions, opening voltage-gated Na+ channels.
    • Conduction Velocity: Determines the speed of action potentials along nerve or muscle fibers.
      • Saltatory Conduction: Increased conduction velocity due to myelination; action potentials jump between nodes of Ranvier.
      • Diameter: Larger diameter increases action potential speed.

    Skeletal Muscle

    • Structure: Voluntary, striated, long cylindrical, multinucleated cells.
    • Myofibrils: Composed of myofilaments—actin (thin) and myosin (thick) arranged in sarcomeres.
      • Thin filaments include actin, troponin, tropomyosin, anchored by nebulin.
      • Thick filaments have myosin heads, ATPase enzymes, and are held by titin.

    Sarcomere Structure

    • Functional Unit: Bounded by adjacent Z discs; main components include:
      • A Band: Dark; includes thick myosin and overlapping thin actin.
      • M Line: Center of A band holding myosin in place.
      • H Zone: Lighter area containing only thick filaments.
      • I Band: Light band with only thin actin filaments.

    Skeletal Muscle Contraction

    • Action potential travels down the sarcolemma and into T-tubules to reach myofibrils.
    • Triggers calcium release from the sarcoplasmic reticulum, exposing binding sites on actin by moving tropomyosin.
    • Cross Bridge Cycle: Myosin binds with actin, sliding thin filaments past thick filaments toward the M line and shortening the sarcomere.

    Muscle Fiber Types

    • Fast Twitch Fibers (Type II):
      • Large for powerful contractions, extensive sarcoplasmic reticulum, and rich in glycolytic enzymes for rapid energy release.
      • Fewer mitochondria and less blood supply than slow fibers, leading to easier fatigue.

    Types of Muscle Contraction

    • Isometric Contraction: Muscle length remains unchanged while tension changes.
    • Isotonic Contraction: Muscle length changes while tension remains constant.
      • Concentric: Muscle shortens.
      • Eccentric: Muscle lengthens.

    Neuromuscular Transmission

    • Synapse Types:
      • Electrical Synapse: Allows fast, bidirectional signal transfer (e.g., cardiac and some smooth muscles).
      • Chemical Synapse: Involves neurotransmitter release across the synaptic cleft; operates unidirectionally with a transmission delay.
    • Motor Unit: Composed of a single motor neuron and the muscle fibers it innervates; crucial for muscle control and movement.

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    Description

    Explore the concepts of membrane potential, including the differences between resting and active states, and the role of refractory periods. Understand how the absolute refractory period prevents action potentials and the mechanisms behind sodium inactivation.

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