Physiology of Nerve Membrane Potentials
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Questions and Answers

What type of stimuli can excite sensory nerve endings in the skin?

  • High temperature
  • Electromagnetic waves
  • Sound waves
  • Mechanical pressure (correct)

    • Electrical current is used to transmit signals between muscle cells in the heart and intestine.

    True

    What is the result of hyperpolarization in a nerve fiber?

    Decreased excitability

    Increasing the voltage of a stimulus can lead to __________ of a nerve fiber.

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

    Match the following types of excitation with their corresponding mechanisms:

    <p>Mechanical pressure = Excites sensory nerve endings Chemical neurotransmitters = Transmit signals between neurons Electrical current = Transmit signals between muscle cells Threshold stimulus = Initiates action potentials</p> Signup and view all the answers

    What happens when a weak negative electrical stimulus is applied to a nerve fiber?

    <p>It may or may not excite the fiber.</p> Signup and view all the answers

    The plateau phase in heart muscle occurs due to the influx of sodium ions.

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

    What is the role of sodium and potassium channels in action potentials?

    <p>They regulate depolarization and repolarization.</p> Signup and view all the answers

    What happens to the membrane potential during the rising phase of an action potential?

    <p>It rises from -70 mV toward 0</p> Signup and view all the answers

    The conductance for sodium ions is greater than that for potassium ions in a resting nerve fiber.

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

    What causes the sudden conformation change in sodium channels during an action potential?

    <p>Inactivation of the activation gate.</p> Signup and view all the answers

    During repolarization, the simultaneous increase in _____ exit speeds up the recovery of the resting membrane potential.

    <p>K+</p> Signup and view all the answers

    Which event occurs immediately after the nerve fiber is excited?

    <p>Sodium channels open in neighboring areas</p> Signup and view all the answers

    Describe the role of Na+ ions in the action potential mechanism.

    <p>Na+ ions increase membrane permeability and flow into the cell, contributing to depolarization.</p> Signup and view all the answers

    Match the phase of action potential to its description:

    <p>Depolarization = Increase in Na+ conductance Repolarization = Increase in K+ conductance Resting potential = Membrane potential around -70 mV Inactivation phase = Closure of Na+ channels</p> Signup and view all the answers

    The plateau phase in heart muscle is primarily due to the prolonged influx of potassium ions.

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

    What occurs first during the repolarization of a nerve fiber?

    <p>Na+ channels close</p> Signup and view all the answers

    The inactivation gate of Na+ channels remains open until the membrane potential returns to the original level.

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

    What is the membrane potential of a neuron at rest?

    <p>-70 millivolts</p> Signup and view all the answers

    During repolarization, _ ions can pour outward through the open ______ channels.

    <p>K+</p> Signup and view all the answers

    Match the following channels with their characteristics:

    <p>Na+ Channels = Have both activation and inactivation gates K+ Channels = Open slower than Na+ channels Both Na+ and K+ Channels = Involved in action potential generation Inactivation Gate of Na+ Channels = Prevents further Na+ flow until repolarization</p> Signup and view all the answers

    What characterizes spontaneous rhythmicity in heart muscle cells?

    <p>Rhythmic electrical activities without external stimuli</p> Signup and view all the answers

    The plateau phase in heart muscle is primarily due to the sustained influx of Ca2+ ions.

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

    What role do voltage-gated K+ channels have during action potential?

    <p>They assist in repolarization.</p> Signup and view all the answers

    Study Notes

    Excitation of Nerve Fibers

    • Different mechanisms are utilized to evoke nerve or muscle action potentials, including mechanical, chemical, and electrical stimuli.
    • Mechanical pressure stimulates sensory nerve endings in the skin, inducing excitability.
    • Chemical neurotransmitters facilitate signal transmission between neurons in the brain.
    • Electrical current transmits signals between muscle cells, particularly in the heart and intestine.

    Action Potential Mechanism

    • A weak negative electrical stimulus may not induce excitation in a nerve fiber until a threshold is reached.
    • Increased voltage of the stimulus leads to action potential generation, whereas insufficient voltage causes hyperpolarization, decreasing fiber excitability.

    Repolarization Process

    • Following the influx of sodium (Na+) ions, Na+ channels close while potassium (K+) channels open, contributing to repolarization.
    • The inactivation gate of Na+ channels remains closed until the membrane potential returns to its original state.

    Voltage-Gated Channels

    • Na+ channels include two gates: activation gate (external) and inactivation gate (internal).
    • During the resting membrane potential of -70 millivolts, Na+ entry is prevented as the activation gate remains closed.
    • When stimulated, the membrane depolarizes, creating a sudden conformational change that opens Na+ channels, allowing Na+ ions to flow inward.

    Resting and Activated States

    • The resting potential is at -70 mV, and during activation, the potential rises towards 0 mV, specifically around -55 mV, indicating the threshold.
    • Activated Na+ and K+ channels facilitate the flow of ions, drastically affecting membrane permeability.

    Propagation of Action Potential

    • The initial excitation in a nerve fiber leads to a local circuit where current flows from depolarized to adjacent resting membrane areas.
    • Upon reaching new areas, sodium channels promptly open, further amplifying the action potential propagation through the fiber.
    • The stabilization of resting membrane potential occurs as the exit of K+ ions increases while Na+ entry decreases, speeding the repolarization process.

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    Action Potential Physiology PDF

    Description

    This quiz covers the mechanisms involved in nerve membrane action potentials and the effects of various stimuli. It discusses how different physiological responses heighten the voltage difference across the nerve membrane, contributing to muscle action. Test your knowledge on the physiological principles and responses related to nerve and muscle functions.

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