Resting membrane potential

• What is the potential difference measured across a cell membrane called?

  Membrane potential
• What is the resting membrane potential?

  The membrane potential in an excitable cell when the cell is at a resting state
• What do cell membranes contain that forms channels?

  Specialized proteins
• Why are different ion channels important?

  They are permeable to different ions
• Which ions have selective ion channels mentioned in the study material?

  K+, Na+, Ca2+, and Cl-
• How is a potential generated by selective K+ permeability?

  • Experiment with chambers separated by a membrane with only potassium channels
  • K+ crosses to compartment 1 down its concentration gradient
  • Na+ cannot move
  • Equilibrium is reached when chemical gradient is balanced by electrical gradient
• What is the concentration of K+ outside and inside the cell?

  K+ outside: 5 mM, K+ inside: 100 mM

  
• What is the concentration of Na+ outside and inside the cell?

  Na+ outside: 150 mM, Na+ inside: 15 mM
• What is the concentration of Ca2+ outside and inside the cell?

  Ca2+ outside: 2 mM, Ca2+ inside: 0.0002 mM
• What is the concentration of Cl- outside and inside the cell?

  Cl- outside: 150 mM, Cl- inside: 13 mM
• How is cellular ion distribution maintained?

  • Combination of selective permeability and ion pumps
  • Most importantly, the Na/K ATPase
  • Na-K pump exchanges 3 internal Na+ for 2 external K+ using ATP

  
• What is the equilibrium potential?

  The potential at which there is no net flow of an ion across the membrane
• How does K+ diffusion occur in astrocytes?

  K+ diffuses down its concentration gradient out of the cell

  
• What affects K+ diffusion in astrocytes?

  Electrostatic repulsion due to the negative inside and positive outside
• What is the Nernst equation used for?

  Calculating the equilibrium potential for a single ion
• What is the equilibrium potential for K+ calculated using the Nernst equation?

  $E_k =$$58 \log \frac{5 \times 10^{-3}}{100 \times 10^{-3}} =$$-75 \text{ mV}$
• What is the equilibrium potential for Na+?

  $E_{Na} =$$+$$40 \text{ mV}$
• What happens if the membrane is permeable to both K+ and Na+?

  Em will lie in-between the equilibrium potentials of K+ and Na+

  
• What is the effect of increasing external potassium on the membrane?

  It depolarizes the membrane, making it more positive

  
• What is the significance of potassium channels in neurons?

  • RMP is close to K+ equilibrium potential
  • Changes in K+ have the most effect on RMP
  • Neurons at rest are mostly permeable to K+
  • Potassium channels are called "leak" channels as they are open all the time
• What is required for a membrane potential to exist?

  • An unequal distribution of ions
  • Selective permeability for that ion via ion channels
  • The membrane potential is influenced by the equilibrium potential of the most permeable ion
• What is the resting membrane potential typically around?

  • 65 mV

  
• What is the role of ATP in the Na-K pump?

  It provides energy for the exchange of ions

  
• What happens to the membrane potential when the membrane is only permeable to K+?

  The membrane potential will be negative

  
• What happens to the membrane potential when the membrane is only permeable to Na+?

  The membrane potential will be positive
• What is the effect of changing K+ concentration on the resting membrane potential?

  It has the most significant effect on RMP

  
• What is the relationship between membrane potential and ion permeability?

  The membrane potential is most influenced by the equilibrium potential of the most permeable ion