Neurophysiology Ion Channels and Transporters Quiz
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Questions and Answers

What does a voltage clamp primarily control?

  • Current
  • Conductance
  • Voltage (correct)
  • Temperature

    • A current clamp measures current while controlling voltage.

    False

    Name one configuration used in patch-clamp techniques.

    Cell-attached, Whole-cell, Outside-out, or Inside-out

    The ______ uses the direct energy of ATP to transport ions against their gradients.

    <p>primary active transport</p> Signup and view all the answers

    Match the following types of transporters with their functions:

    <p>Antiporter = Ions move in opposite directions Symporter = Ions move in the same direction Cotransporters = Use primary transport to facilitate movement</p> Signup and view all the answers

    Which of the following describes a characteristic of ligand-gated ion channels?

    <p>They open in response to a ligand binding.</p> Signup and view all the answers

    What defines the selectivity of an ion channel?

    <p>Which ions can pass through it</p> Signup and view all the answers

    All ion channels have the same gating mechanisms.

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

    What is the formula to calculate the number of moles of ions?

    <p>$\mathrm{\text{Moles of ions}} = \frac{Q}{F}$</p> Signup and view all the answers

    K+ ions are preferentially permeable compared to Na+ ions due to their larger size.

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

    What mechanism allows K+ ions to pass smoothly through the selectivity filter in K+ channels?

    <p>K+ ions become fully dehydrated and fit precisely into the filter's carbonyl oxygen coordination sites.</p> Signup and view all the answers

    The number of ions required to change a cell's potential from 0 mV to --80 mV is greater than the number of total ions present in the cell.

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

    The ___________ structure has four subunits and is responsible for voltage sensing in Na+ channels.

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

    What constant is represented by $N_A$ in the equation for the number of ions?

    <p>Avogadro's number</p> Signup and view all the answers

    The drift flux is defined by the formula $J_{drift} = \sigma \cdot E$, where E is the ________.

    <p>electric field</p> Signup and view all the answers

    Match the following K+ channel types with the number of genes associated with them:

    <p>Voltage-gated Kv channels = 40 genes Ca2+-activated (KCa) channels = 5 genes Two-pore (K2P) channels = 15 genes Inward-rectifying (KIR) channels = 15 genes</p> Signup and view all the answers

    In the context of drift and diffusion, what does the letter 'D' represent in Fick's Law?

    <p>Diffusion coefficient</p> Signup and view all the answers

    What is the role of the intracellular loops in K+ channels?

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

    Na+ ions can easily dehydrate and fit into the selectivity filter of K+ channels.

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

    Match the following terms with their definitions:

    <p>Drift Flux = Flow of particles due to electric field Diffusion Flux = Flow of particles due to concentration gradient Electrical Conductivity = Ability of a material to conduct electric current Mobility = Ease of movement of ions under an electric field</p> Signup and view all the answers

    Explain why Na+ ions get stuck in the selectivity filter of K+ channels.

    <p>Na+ ions have stronger interactions with water molecules, making it difficult for them to fully dehydrate and fit into the coordination sites.</p> Signup and view all the answers

    According to Ohm's Law, doubling the concentration of ions will result in double the drift.

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

    In the drift flux formula, the symbol $μ$ represents the ________ of the ions.

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

    What happens to the membrane potential $V_m$ when the current $I_m$ is positive?

    <p>It increases above $E_R$.</p> Signup and view all the answers

    At steady state, the rate of change of membrane potential $V_m$ is zero.

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

    What is the equation for the membrane potential over time?

    <p>V_m = E_R + \frac{I_m}{g_m} \cdot \left( 1 - e^{\left( \frac{- t}{\tau} \right)} \right)</p> Signup and view all the answers

    In an isopotential sphere, the voltage is __________ across the membrane.

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

    What does $ au$ represent in the equations provided?

    <p>Time constant</p> Signup and view all the answers

    As the membrane potential $V_m$ approaches the resting potential $E_R$, the change in voltage $\frac{dV_m}{dt}$ increases.

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

    Write the equation for the change in membrane potential $\Delta V_m(t)$ over time.

    <p>\Delta V_m(t) = I_m \cdot R_m \cdot \left( 1 - e^{\left( \frac{- t}{\tau} \right)} \right)</p> Signup and view all the answers

    Which of the following statements about Na+ channels is correct?

    <p>Na+ channels decrease depolarization and increase hyperpolarization.</p> Signup and view all the answers

    Phenytoin has a mechanism that enhances the recovery from inactivation of Na+ channels.

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

    What happens at the resting membrane potential?

    <p>The rate of change of voltage is zero.</p> Signup and view all the answers

    What is the primary goal of epilepsy treatment strategies?

    <p>Restore balance between excitation and inhibition.</p> Signup and view all the answers

    During action potential, the inside of the axon becomes ______ charged.

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

    The IV curve of a neuron shows that a positive current makes the extracellular environment more negative.

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

    What equation represents the relationship between current and voltage for a capacitor?

    <p>I = C * dV/dt</p> Signup and view all the answers

    Match the following types of channels to their effect on depolarization:

    <p>Na+ channel = Decreases depolarization K+ channel = Increases depolarization</p> Signup and view all the answers

    Which drug is NOT commonly used for epilepsy treatment?

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

    At rest, the resting membrane potential, V_rest, is calculated using the _____ equation.

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

    Match the following components with their respective properties:

    <p>Resistor = Charges move through Capacitor = Charges accumulate on both sides IV Curve = Describes current-voltage relationship Conductance = Proportional to the flow of current</p> Signup and view all the answers

    The Sodium Hypothesis explains the positive membrane potential detected during action potential.

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

    Which of the following represents the equation for the IV curve of a resistor?

    <p>I = ΔV / R</p> Signup and view all the answers

    What role do T-type Ca2+ channels have in absence epilepsy?

    <p>They are involved in burst firing and corticothalamic feedback.</p> Signup and view all the answers

    The diameter of most axons is less than _____ mm.

    <p>0.2</p> Signup and view all the answers

    At equilibrium, the total current (I) is equal to zero.

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

    What does the term 'reversal potential' refer to in the context of electrical circuits?

    <p>It is the membrane potential at which there is no net current flow for a given ion.</p> Signup and view all the answers

    Study Notes

    Comparing Electronic Circuits and Neurons

    • Electronic circuits use electrons as charge carriers, while neurons use ions.
    • Current (I) is defined as the flow of positive charge.
    • Kirchhoff's Current Law: The sum of currents entering a node equals the sum of currents leaving it.
    • Kirchhoff's Voltage Law: The sum of potential differences around a closed loop is zero.
    • Electric Potential (V) is the potential difference between two points.
    • Membrane Potential is the difference in potential between the inside and outside of a membrane.
    • Force (F) in an electric field (E) is equal to charge (q) times the field strength (F = qE).
    • Electric field (E) is the gradient of the electric potential (E = -dV/dx).
    • Space-Charge Neutrality: In any given volume, the total positive charge approximately equals the total negative charge.

    Capacitance and Charge on the Membrane

    • Amount of charge (Q) needed to establish membrane potential (ΔV) over capacitance (C) is Q = CΔV.
    • Faraday's Constant (F): The charge of a mole of ions (96485 C/mol).
    • Number of ions = (moles of ions * Avogadro's Number (6.022 × 1023) / Faraday's Constant).
    • Drift flux (Jdrift) is the flow of particles due to the electric field (Jdrift = σE).
    • Electrical conductivity (σ), and E is the electric field (E = -dV/dx).

    Ion Permeability and Donnan Equilibrium

    • Most cell membranes are permeable to potassium (K+) and chloride (Cl-).
    • Membrane potential should equal the equilibrium potentials of all permeable ions if there's no active transport.

    Membrane Permeability and Flux Equation

    • Flux (J) is the rate of ion movement across the membrane.
    • J = -PΔ[C], where P is permeability and Δ[C] is the concentration difference across the membrane.

    Goldman-Hodgkin-Katz (GHK) Current Equation

    • Describes the ionic current (I) across a membrane, assuming a constant electric field and considering multiple ion species.
    • I = PionZionF[C]ion(ΔV / RT), where: Pion is permeability, Zion is valence, F is Faraday's constant, [C]ion is concentration, ΔV is membrane potential, R is gas constant, and T is temperature.

    Voltage Equation

    • The membrane resting potential (Vrest) is calculated using the GHK current equation when the total net current equals zero.

    Isopotential Sphere vs Cylinder

    • Isopotential sphere: Voltage uniform across the membrane.
    • Cylinder: Voltage varies along the membrane's axis.
    • Membrane resistance (rm) , membrane capacitance (Cm), and Internal resistance (ra) are critical parameters in cable models of the membrane.

    Length and Time Constants

    • Space constant (λ): Distance needed to reach 37% of maximum voltage change from the resting potential. λ = √(rm/ra).
    • Time constant (τ): Time required to reach 63% of maximum voltage change from resting potential. τ = rmCm.

    Conduction Velocity

    • Conduction velocity (θ) is the speed at which the action potential propagates. θ = 2λ/τm.

    Current in Extracellular Space

    • Current flows in extracellular space, creating small potential differences, and resistance to current flow.

    Signal Range

    • Signals range from tens of µV to a few mV.
    • Waveform depends on cell type, morphology, and recording location.

    Extracellular Recordings

    • Single electrodes (glass/microwires).
    • Multiple electrodes (tetrodes/silicon probes).
    • Recording locations vary depending on the measurement.

    Intracellular Recordings

    • Sharp electrodes.
    • Whole-cell patch-clamp.
    • In vivo two-photon patching.

    Voltage Clamp Technique

    • Records voltage and measures current required to hold voltage at a particular level.

    Structure-Function Relationship

    • Ion channels are selective, gated (open/close), and inactivated.

    Ion Channels vs Transporters

    • Channels allow ions to move down electrochemical gradients.
    • Transporters actively move ions against electrochemical gradients using energy (like ATP).

    Voltage-Gated K+ Channels

    • Tetrameric structure made of 4 subunits.
    • Channels have S1-S4 voltage sensing domains, P regions (ion selectivity), and S5-S6 gating pore regions.
    • Channels are involved in maintaining sodium concentration gradients, thereby contributing to the resting potential.

    K+ Selectivity Filter Mechanism & Na+ Exclusion

    • The selectivity filter prefers K+ ions due to their size and hydration.
    • Na+ ions are too small to effectively interact with the carbonyl oxygens, making their passage less favorable.

    Conductance and Gating Currents

    • Conductance changes with membrane potential
    • Voltage-dependent gating mechanisms control channel openings.

    Synaptic Transmission - overview

    • Presynaptic terminal contains vesicles holding neurotransmitters.
    • Action potentials cause calcium influx to trigger neurotransmitter release.
    • Neurotransmitters bind to receptors on the postsynaptic membrane, causing an effect (depolarization, hyperpolarization).

    Different Types of Synapses

    • Chemical synapses use neurotransmitters.
    • Gap junctions allow direct passage of ions.

    Neurotransmitter Release Mechanisms

    • Depolarization at the presynaptic terminal triggers Calcium influx.
    • Calcium activates proteins and moves vesicles toward the membrane, and then fusion to release the neurotransmitter.

    Clustering of Presynaptic Calcium Channels

    • Clustering increases the probability of neurotransmitter release to respond to action potentials efficiently.
    • Dependency on calcium concentration is dependent on the fourth power so the release enhances the quick initiation and termination of the release mechanism.

    Synaptic Vesicle Cycle

    • Endocytosis and exocytosis cycles bring vesicles back from the plasma membrane, including clathrin-mediated endocytosis.

    Neurotransmitters - Fast Acting vs. Slow Acting

    • Fast acting neurotransmitters (e.g., glutamate, GABA) act rapidly through ion channel receptors.
    • Slow acting neurotransmitters (e.g., neuropeptides) act more slowly through G protein-coupled receptors.

    Neurotransmitter uptake and recycling

    • Different neurotransmitters use various uptake mechanisms to clear out from the synapse.

    Chloride Reversal Potential

    • GABA receptors produce chloride influx to increase negative intracellular potential, which can result in inhibition.
    • The effects of chloride depend on the membrane potential and concentration differences.

    Epileptic Seizures

    • Abnormal excitability causes neurons to generate action potentials too easily.

    Epilepsy Treatment Strategies

    • Restore balance between excitation and inhibition is the primary goal.
    • Prevent long-lasting depolarization, and prevent high-frequency, synchronous firing are important to avoid prolonged activity.

    Membrane Potential Over Time

    • The membrane potential changes over time as different ions move across the membrane.
    • The time constant determines how quickly the membrane potential changes.

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    Description

    Test your knowledge on the mechanisms of ion channels and transporters in neurophysiology. This quiz covers concepts such as voltage clamping, ligand-gated ion channels, and ion selectivity. Perfect for students studying neuroscience or related fields.

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