Membranes and Receptors Module, Lecture 3.1
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Questions and Answers

What is the primary factor that determines the resting membrane potential in nerves and muscles?

  • Cl- concentration outside the cell
  • K+ concentration across the cell membrane (correct)
  • Na+ concentration inside the cell
  • Organic anions trapped inside the cell

    • What occurs at the Nernst potential for an ion?

  • Net movement of ions across the membrane reaches maximum
  • Net diffusion of ions across the membrane stops (correct)
  • Electrical gradients are equal to chemical gradients
  • Concentration gradient dominates electrical gradient

    • Which statement describes the relationship between electrical and chemical gradients for K+?

  • Chemical gradient favors K+ to enter the cell
  • Both gradients favor K+ to leave the cell
  • Electrical gradient moves K+ into the cell while the chemical gradient favors K+ to leave (correct)
  • Electrical gradient favors K+ to stay out of the cell

    • What is the impact of the cell membrane acting as an insulator?

    <p>Facilitates the separation of electrical charges</p> Signup and view all the answers

    At what temperature is the Nernst equation typically used for calculations related to K+ equilibrium potential?

    <p>37 ºC</p> Signup and view all the answers

    What does Vm represent in the context of membrane potential?

    <p>Membrane potential difference</p> Signup and view all the answers

    Which of the following ions is primarily responsible for establishing the electrical disequilibrium across the cell membrane?

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

    How does the electrical force affect K+ ions in relation to the negative charges within the cell?

    <p>It attracts K+ ions into the cell</p> Signup and view all the answers

    What is the typical range of resting membrane potentials in animal cells?

    <p>-20 to -90 mV</p> Signup and view all the answers

    Which characteristic describes the selectivity of ion channels in cell membranes?

    <p>Only permits specific ion species</p> Signup and view all the answers

    How is membrane potential specifically measured?

    <p>As the potential inside the cell relative to the outside</p> Signup and view all the answers

    What does the Nernst equation calculate?

    <p>The equilibrium potential for an ion</p> Signup and view all the answers

    Which ion has a valency of +1 in the Nernst equation?

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

    What effect does selective permeability have on the resting membrane potential?

    <p>It allows specific ions to influence the potential difference</p> Signup and view all the answers

    At a temperature of 37°C, what value is commonly used for the conversion in the Nernst equation?

    <p>63 mV</p> Signup and view all the answers

    What happens during the gating of ion channels?

    <p>Channels can open or close based on conformational changes</p> Signup and view all the answers

    Why are ion channels critical in cellular signaling?

    <p>They facilitate movement of ions down their electrochemical gradient.</p> Signup and view all the answers

    What is the equilibrium potential for K+ calculated when the outside concentration is 4.0 mEq/L and inside concentration is 140 mEq/L?

    <p>-94 mV</p> Signup and view all the answers

    Which of the following ions is NOT typically selective for ion channels?

    <p>Mg2+</p> Signup and view all the answers

    How does the resting membrane potential of skeletal muscle compare to EK?

    <p>It is close to but not equal to EK</p> Signup and view all the answers

    What happens to Na+ at the equilibrium potential when the inside of the cell becomes positively charged?

    <p>Na+ flows out of the cell</p> Signup and view all the answers

    How does the extracellular ion concentration influence equilibrium potential?

    <p>Higher extracellular concentration leads to higher equilibrium potential.</p> Signup and view all the answers

    Which of the following processes is NOT primarily dependent on changes in membrane potentials?

    <p>Cell division</p> Signup and view all the answers

    What is the role of K+ channels during the resting membrane potential?

    <p>They are open to stabilize the potential</p> Signup and view all the answers

    Which ion has a higher concentration inside a typical mammalian cell compared to outside?

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

    What is the main reason for the negative charge inside the cell during resting potential?

    <p>Presence of negatively charged A- ions inside the cell</p> Signup and view all the answers

    Which ions primarily contribute to the resting membrane potential?

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

    What occurs when K+ channels are open at rest?

    <p>K+ diffuses out of the cell</p> Signup and view all the answers

    What is the approximate extracellular concentration of Na+ in mM?

    <p>145 mM</p> Signup and view all the answers

    How does the presence of large intracellular proteins affect the membrane potential?

    <p>They contribute to the negative charge inside the cell.</p> Signup and view all the answers

    What happens to the membrane potential when K+ reaches equilibrium?

    <p>The net movement of K+ stops.</p> Signup and view all the answers

    Which of the following statements is true regarding ion distribution in a resting mammalian cell?

    <p>A- ions are predominantly found inside the cell.</p> Signup and view all the answers

    Study Notes

    Membranes and Receptors Module, Session 3, Lecture 3.1: The Resting Cell Membrane and Potential

    • The lecture covers the resting membrane potential in cells.
    • The membrane potential is an electrical potential difference across the plasma membrane of a normal living cell.
    • Electrical potential is measured in millivolts.
    • Animal cells typically have a negative resting membrane potential ranging from −20 to −90 mV.
    • Membrane potentials are expressed as the potential inside the cell relative to the extracellular solution.
    • The resting membrane potential is crucial for signaling in the nervous system and many other cell types.

    Objectives of the Lecture

    • To understand the membrane potential in cells.
    • To outline how membrane potentials are established and modified by cellular signaling mechanisms.
    • To explain equilibrium potential for an ion, and calculate its value from ionic concentrations on either side of the membrane.

    Objective 1: Understanding Membrane Potential

    • All cells possess an electrical potential (voltage) difference across their plasma membrane.
    • This membrane potential is the basis of signaling in the nervous system and other cells.
    • The resting membrane potential is the electrical potential difference across the plasma membrane of a living cell under normal conditions.

    Objective 2: Establishing and Modifying Membrane Potentials

    • Membrane potentials arise from selective permeability of the cell membrane.
    • The membrane is selectively permeable to specific ions.
    • Permeability to ions occurs through channel proteins (ion channels).
    • Ion channels are characterized by:
      • Selectivity: allowing only specific ions to pass.
      • Gating: opening and closing due to conformational changes in the protein.
      • High rate of ion flow down their electrochemical gradient.

    Setting up the Resting Potential: Ionic Concentrations

    • Intracellular ion concentrations (millimolar):
      • Na⁺: 10 mM
      • K⁺: 160 mM
      • Cl⁻: 3 mM
      • A⁻: 167 mM
    • Extracellular ion concentrations (millimolar):
      • Na⁺: 145 mM
      • K⁺: 4.5 mM
      • Cl⁻: 114 mM
      • A⁻: 40 mM
      • A⁻ represents anions other than chloride (e.g., phosphate ions, charged protein groups).

    Maintaining Electrical Disequilibrium

    • The asymmetric distribution of ions across the membrane creates an electrical disequilibrium resulting in a membrane potential difference.
    • The unequal charge separation is essential for cellular function.
    • The cell membrane acts as an insulator.

    Electrochemical Gradient

    • Both electrical gradients and chemical ones contribute to the movement of ions across the cell membrane.
    • An electrical force drives ions toward areas of opposite charge.
    • Concentration gradient (chemical gradient) leads to movement from high to low concentrations.

    Membrane Potential (Objective 1)

    • The resting membrane potential for nerves & muscles is from -40 to −90 mV.
    • The resting membrane potential is primarily determined by the potassium (K⁺) ion.

    Objective 3: Equilibrium Potential

    • The equilibrium potential for an ion is the membrane potential at which the net flow of that ion across the membrane is zero due to the balance of electrical and chemical gradients.
    • The Nernst equation calculates the equilibrium potential of an ion.

    Nernst Equation

    • The Nernst equation, used for calculation: Eion = (RT/ZF) × ln ([ion]out/[ion]in)

    • Constants:

      • R = gas constant
      • T = temperature (in Kelvin)
      • Z = valence of the ion
      • F = Faraday's constant

    • Important Considerations:

      • The values of the constants are usually pre-calculated for a specific temperature (e.g., 37°C).
      • log₁₀ is generally used instead of ln.

    Equilibrium Potential Calculation Examples

    • A specific example provides the equations and the results to determine the equilibrium potential given cell and extra-cellular concentration of the relevant ions and charges.
    • The example calculations are for K⁺ and Na⁺.

    Changing Membrane Potentials

    • Changes in membrane potential are fundamental in many cellular processes like nerve signaling and muscle contraction.
    • These changes can occur from action potentials and triggering muscle contraction to controlling hormone and neurotransmitter secretion to sensory transduction.

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    Related Documents

    Lec 3-1 THE RESTING CELL MEMBRANE POTENTIAL PDF

    Description

    This lecture focuses on the resting cell membrane potential, an essential electrical difference across the plasma membrane of living cells. It discusses how this potential influences signaling in the nervous system and details the factors that establish and modify membrane potentials. Attendees will learn to calculate the equilibrium potential for specific ions based on their concentrations.

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