Action potential
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Questions and Answers

What is the primary function of sensory receptors in an organism?

  • To detect changes in the environment (correct)
  • To transmit nerve impulses
  • To coordinate responses from the brain
  • To generate muscle contractions
  • What is the resting potential of a neuron?

  • A negative charge across the neurone membrane (correct)
  • Equal distribution of electrical charges
  • No change in electrical charge
  • A positive charge across the neurone membrane
  • What initiates the action potential in a neuron?

  • Increased permeability to sodium ions (correct)
  • Stimulation of effector muscles
  • Decreased potassium ion movement
  • Movement of chloride ions
  • Which ions predominantly move across the neurone membrane during the action potential?

    <p>Sodium and potassium ions</p> Signup and view all the answers

    What type of ion channels are responsible for the rapid influx of sodium ions during the action potential?

    <p>Gated ion channels</p> Signup and view all the answers

    What primarily determines the resting membrane potential in a neurone?

    <p>Distribution of ions across the membrane</p> Signup and view all the answers

    What is the role of the central nervous system in the neuron signaling process?

    <p>To coordinate responses based on sensory input</p> Signup and view all the answers

    Which configuration describes the state of the neurone membrane prior to action potential generation?

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

    During the action potential, which ion's conductance increases first?

    <p>Sodium (Na+)</p> Signup and view all the answers

    What does the sodium-potassium pump primarily function to do?

    <p>Transport sodium and potassium ions</p> Signup and view all the answers

    What occurs during the repolarization phase of an action potential?

    <p>K+ conductance becomes much higher than Na+ conductance</p> Signup and view all the answers

    Which ion channel type is responsible for maintaining resting potential?

    <p>Leakage (nongated) channels</p> Signup and view all the answers

    What is the main impact of the hyperpolarizing afterpotential?

    <p>Inhibits action potential generation</p> Signup and view all the answers

    How is conduction velocity along a nerve fibre increased?

    <p>Increasing nerve diameter</p> Signup and view all the answers

    What is the significance of having more sensory receptors in an area?

    <p>Enhances sensitivity to stimuli</p> Signup and view all the answers

    What does the time constant (τ) refer to in the context of nerve physiology?

    <p>Time required for a cell membrane to depolarize or hyperpolarize</p> Signup and view all the answers

    What initiates the local circuit of depolarization along the nerve fibre?

    <p>Inward current from the depolarized region</p> Signup and view all the answers

    Which ion primarily floods into the neurone during depolarization?

    <p>Sodium (Na+)</p> Signup and view all the answers

    What is the role of myelin in nerve fibers?

    <p>It decreases ion flow through the membrane.</p> Signup and view all the answers

    What triggers the release of acetylcholine at the neuromuscular junction?

    <p>Opening of calcium channels.</p> Signup and view all the answers

    What happens to Na+ channels upon the binding of acetylcholine at the motor end plate?

    <p>They open, allowing Na+ to enter the muscle cell.</p> Signup and view all the answers

    Which structure contains acetylcholine in the neuromuscular junction?

    <p>Terminal button</p> Signup and view all the answers

    What is the functional significance of the Node of Ranvier in myelinated fibers?

    <p>It allows action potentials to occur only at specific sites.</p> Signup and view all the answers

    What is the valence of calcium ions (Ca2+)?

    <p>+2</p> Signup and view all the answers

    How is the resting membrane potential calculated?

    <p>Using the Golman equation</p> Signup and view all the answers

    What is the significance of the concentration gradient in resting membrane potentials?

    <p>It balances the electrical charge</p> Signup and view all the answers

    What formula gives the equilibrium potential for sodium (Na+)?

    <p>$E (mV) = 58.log10 \frac{Co}{Ci}$</p> Signup and view all the answers

    At what temperature is the equation $E (mV) = 61.log10 \frac{Co}{Ci}$ simplified for use?

    <p>37°C</p> Signup and view all the answers

    For sodium ions, if the concentration outside the cell is 150 and inside is 15, what is the value of E (mV)?

    <p>+58 mV</p> Signup and view all the answers

    What primarily determines the resting membrane potential?

    <p>Permeability to various ions</p> Signup and view all the answers

    Which of the following ions has a valence of -1?

    <p>Chloride (Cl-)</p> Signup and view all the answers

    What is the general role of nerve and muscle cells regarding resting membrane potential?

    <p>They generate action potentials.</p> Signup and view all the answers

    At 20°C, how is the equation for equilibrium potential adjusted?

    <p>It requires a different constant.</p> Signup and view all the answers

    What type of gated ion channel responds to voltage changes?

    <p>Voltage-gated channels</p> Signup and view all the answers

    What is the primary role of ligand-gated channels?

    <p>To open in response to specific chemical stimuli</p> Signup and view all the answers

    During which phase of the action potential does depolarization occur?

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

    What effect does an action potential primarily have on membrane potential?

    <p>It causes a potential difference of approximately +40mV</p> Signup and view all the answers

    What is the term for the period when a region behind an action potential cannot generate a new one?

    <p>Refractory period</p> Signup and view all the answers

    How is the membrane potential conventionally measured?

    <p>Outside of the cell is always zero</p> Signup and view all the answers

    What defines the equilibrium potential?

    <p>A potential difference that balances chemical and electrical forces</p> Signup and view all the answers

    What is the Nernst equation used for?

    <p>To calculate equilibrium potential</p> Signup and view all the answers

    Which of the following channels are always open?

    <p>Leakage channels</p> Signup and view all the answers

    Which stage immediately follows depolarization in an action potential?

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

    Study Notes

    Neuronal Membrane Potential

    • Resting neurone membrane exhibits a negative charge inside (-70mV to -80mV) and a positive charge outside due to ion distribution.
    • High permeability to K+ and Cl- establishes a resting membrane potential close to equilibrium potential.
    • Low permeability to Na+ and Ca2+ keeps resting membrane far from their equilibrium potential.

    Action Potential Phases

    • Resting Membrane Potential: Around -70mV with high K+ conductance and low Na+ conductance.
    • Depolarization: Inward current causes membrane to depolarize, leading to increased Na+ channel permeability.
    • Repolarization: Na+ channels close slowly, K+ channels open rapidly, significantly increasing K+ conductance.
    • Hyperpolarizing Afterpotential: K+ conductance remains higher than resting levels, resulting in undershoot.

    Conduction Mechanism

    • Temporary depolarization causes a local circuit effect, facilitating electrical impulse spread to adjacent resting areas.
    • Voltage-gated Na+ channels are activated, allowing sodium influx and generating an action potential.
    • Action potentials propagate with specific conduction velocities.

    Factors Influencing Conduction Velocity

    • Increased nerve diameter enhances conduction speed.
    • Ion valences affect electrical properties; Na+ & K+ (+1), Cl- (-1), Ca2+ (+2).
    • Temperature influences neuronal activity.

    Equilibrium Potentials Calculation

    • Using the formula: E (mV) = 58.log10(Co/Ci) with adjustments for valence (z) and temperature.
    • Calculated equilibrium potential for Na+ is +58mV, based on extracellular (150mM) and intracellular (15mM) concentrations.

    Membrane Potential Characteristics

    • Resting potential arises from polarization; the inside of the cell is compared to the outside, which is considered zero.
    • Changes in electrical charges are managed through sodium and potassium ion movements.

    Types of Ion Channels

    • Gated Channels: Open in response to stimuli (voltage, ligands, mechanical pressure).
    • Leakage Channels: Always open, allowing continuous ion movement.
    • Ion diffusion can significantly exceed predictive rates due to selective permeability.

    Neuromuscular Junction Components

    • Motor units consist of a motor neuron and the muscle fibers they innervate.
    • The junction is chemically linked by acetylcholine, released from vesicles at the axon terminal.
    • The synaptic cleft (20-30 nm) separates the axon terminal from muscle cell membranes.

    Events at the Neuromuscular Junction

    • An action potential at the axon terminal opens Ca2+ channels, triggering acetylcholine release.
    • Acetylcholine binds to receptors on the motor end plate, opening Na+ channels and generating depolarization (end plate potential).
    • Na+ entry leads to action potential initiation in muscle fibers, facilitating contraction.

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    Description

    This quiz explores the concepts surrounding the resting membrane potential of neurons, focusing on ion distribution and membrane permeability. Learn how different ions contribute to the electrical balance across the neuron's membrane and understand the significance of equilibrium potential in maintaining this state.

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