Resting Membrane Potential (RMP) in Excitable Cells
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Questions and Answers

What is the primary reason for the unequal distribution of ions in the ECF and cytosol?

  • The Na/K ATPases pump out sodium ions but not potassium ions.
  • The plasma membrane has more K leak channels than Na leak channels. (correct)
  • The ECF has a higher concentration of potassium ions than sodium ions.
  • The cytosol has a higher concentration of sodium ions than potassium ions.

    • What would be the effect on the resting membrane potential if the plasma membrane had more Na leak channels than K leak channels?

  • The resting membrane potential would remain unchanged.
  • The inside of the membrane would become more negative.
  • The inside of the membrane would become more positive. (correct)
  • The outside of the membrane would become more negative.

    • Why do anions not follow potassium ions out of the cell?

  • Anions are not affected by the concentration gradient.
  • Anions are attached to non-diffusible molecules such as ATP and large proteins. (correct)
  • Anions are positively charged and repel each other.
  • Anions are unable to diffuse through the plasma membrane.

    • What is the function of the Na/K ATPases in maintaining the resting membrane potential?

    <p>To pump out sodium ions as fast as they leak in and bring in potassium ions.</p> Signup and view all the answers

    Why are the Na/K ATPases considered electrogenic?

    <p>Because they pump out more positive charges than they bring into the cell.</p> Signup and view all the answers

    What is the net effect of the Na/K ATPases on the resting membrane potential?

    <p>It becomes more negative.</p> Signup and view all the answers

    What is the ratio of sodium ions pumped out of the cell to potassium ions pumped into the cell by the Na/K ATPases?

    <p>3:2</p> Signup and view all the answers

    What is the main factor that contributes to the inside-negative resting membrane potential of a cell?

    <p>The unequal distribution of ions in the ECF and cytosol.</p> Signup and view all the answers

    What is the primary cause of the resting membrane potential?

    <p>Unequal distribution of ions in the ECF and cytosol</p> Signup and view all the answers

    What is the typical value of the resting membrane potential in neurons?

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

    What is the purpose of the reference electrode in measuring the resting membrane potential?

    <p>To provide a point of reference for the recording microelectrode</p> Signup and view all the answers

    What is the significance of the minus sign in the resting membrane potential?

    <p>It indicates that the inside of the cell is negative relative to the outside</p> Signup and view all the answers

    What is the main cation in the cytosol?

    <p>Potassium (K)</p> Signup and view all the answers

    What is the instrument used to detect the electrical difference across the plasma membrane?

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

    What is the term used to describe a cell that shows a membrane potential?

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

    What is the dominant anion in the cytosol?

    <p>All of the above</p> Signup and view all the answers

    What is the main reason for the stimulus artefact in the action potential curve?

    <p>Leakage of current from the stimulating electrode to the recording electrode</p> Signup and view all the answers

    What is the duration of the latent period in the action potential curve?

    <p>0.5-1 ms</p> Signup and view all the answers

    What is the value of the resting membrane potential in the given action potential curve?

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

    What is the charge at the anode in the given action potential curve?

    <p>-ve charge</p> Signup and view all the answers

    What is the direction of ion movement during depolarization in the given action potential curve?

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

    What is the phase of the action potential curve that occurs between points c and d?

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

    What is the value of the reversal of polarity (over shoot) in the given action potential curve?

    <p>+35 mV</p> Signup and view all the answers

    What is the phase of the action potential curve that occurs between points e and f?

    <p>After hyperpolarization</p> Signup and view all the answers

    What is the potential at which depolarization occurs very rapidly?

    <p>-55 mV</p> Signup and view all the answers

    What is the duration of the spike potential in an axon?

    <p>1 ms</p> Signup and view all the answers

    What is the term for the phase of rapid rise of potential in depolarization and a rapid fall in repolarization phase?

    <p>Spike potential</p> Signup and view all the answers

    What is the primary reason why Na+ cannot enter the cell during the resting membrane potential?

    <p>The membrane is impermeable to Na+</p> Signup and view all the answers

    What is the term for the phase of slow repolarization that follows the rapid fall in spike potential?

    <p>Phase of negative after potential</p> Signup and view all the answers

    What is the resting membrane potential due to?

    <p>Distribution of more cations outside the cell membrane and more anions inside the cell membrane</p> Signup and view all the answers

    What is the term for the phase of rapid fall in potential after the spike potential?

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

    What is the reason for the rapid increase in permeability for Na+ ions during the depolarization phase?

    <p>Opening of voltage-gated Na+ channels</p> Signup and view all the answers

    What is the primary mechanism by which the membrane potential changes rapidly during an action potential?

    <p>Rapid influx of Na+ ions into the cell</p> Signup and view all the answers

    What is the role of calcium ions in the development of action potential?

    <p>Calcium ions have a dual role, where low extracellular Ca2+ concentration increases excitability and high concentration stabilizes the membrane</p> Signup and view all the answers

    During the rapid repolarization phase, which of the following occurs?

    <p>K+ channels open up and Na+ channels remain closed</p> Signup and view all the answers

    What is the role of the Na+-K+ ATPase pump in the restoration of the resting membrane potential?

    <p>The pump results in the efflux of three Na+ and influx of two K+ ions</p> Signup and view all the answers

    What is the effect of low extracellular Ca2+ concentration on the excitability of nerve and muscle?

    <p>It increases the excitability of nerve and muscle</p> Signup and view all the answers

    During the depolarization phase, which of the following occurs?

    <p>Na+ channels open up and K+ channels remain closed</p> Signup and view all the answers

    What is the role of the slow calcium channels in the development of action potential?

    <p>They open up and admit Ca2+ ions during the development of action potential</p> Signup and view all the answers

    What is the Hodgkin cycle?

    <p>A positive feedback spiral that results in rapid change in membrane potential</p> Signup and view all the answers

    Study Notes

    Resting Membrane Potential (RMP)

    • RMP is an electrical potential difference (voltage) across the membrane in excitable cells
    • Occurs due to the buildup of negative ions in the cytosol and an equal buildup of positive ions in the extracellular fluid (ECF) along the outside surface of the membrane
    • Separation of positive and negative electrical charges creates potential energy, measured in volts or millivolts (1 mV = 0.001 V)
    • Greater difference in charge across the membrane results in a larger membrane potential (voltage)

    Measurement of RMP

    • Measured using a recording microelectrode inserted inside the cell and a reference electrode placed outside the cell in the ECF
    • Both electrodes are connected to a voltmeter, which detects the electrical difference (voltage) across the plasma membrane

    RMP in Neurons

    • Ranges from 40 to 90 mV, with a typical value of 70 mV
    • Minus sign indicates that the inside of the cell is negative relative to the outside
    • A cell with a membrane potential is said to be polarized

    Factors Contributing to RMP

    • Unequal distribution of ions in the ECF and cytosol (major factor)
      • ECF is rich in Na and Cl- ions, while cytosol is rich in K ions and anions such as phosphates and amino acids
      • Plasma membrane has more K leak channels than Na leak channels, resulting in a greater number of potassium ions diffusing out of the cell and more positive ions entering the cell
    • Inability of most anions to leave the cell
      • Most anions inside the cell are attached to non-diffusible molecules, preventing them from leaving the cell
    • Electrogenic nature of Na/K ATPases
      • These pumps help maintain the RMP by pumping out Na and bringing in K, contributing to the negativity of the RMP

    Action Potential

    • Recording of action potential of a large mammalian myelinated nerve fiber has several components:
      • Stimulus artifact
      • Latent period
      • Firing level
      • Overshoot
      • Spike potential
      • Repolarization
      • After depolarization
      • After hyperpolarization

    Role of Voltage-Gated Na+ and K+ Channels

    • Development of action potential was studied by Hodgkin and Huxley using the voltage clamp technique
    • According to the Hodgkin-Huxley theory, the sequence of events is:
      • Polarization phase
      • Depolarization phase
      • Repolarization phase
      • After depolarization and hyperpolarization phases
    • Ionic basis of action potential:
      • Depolarization phase: increase in permeability of the membrane for Na+ ions, leading to rapid influx of Na+ ions into the cell
      • Repolarization phase: rapid efflux of K+ ions from the cell

    Role of Calcium Ions

    • Ca2+ ions also play a role in the development of action potential
    • Concentration of Ca2+ in ICF is very low compared to ECF
    • When Na+ channels are open, some Ca2+ ions move inside the cell through these channels
    • Separate class of slow calcium channels also exists in the cell membrane, which open up during the development of action potential

    Important Note

    • Low extracellular Ca2+ concentration increases the excitability of nerve and muscle by decreasing the amount of depolarization necessary for initiating changes in Na+ and K+ conductance required for action potential
    • Increase in Ca2+ concentration stabilizes the membrane by decreasing excitability

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    Description

    Learn about the electrical potential difference across the membrane in excitable cells, caused by the buildup of ions on either side of the membrane.

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