Lecture 3: Ion Currents and Potentials II

Question 1

Why is the membrane potential at rest closer to the Nernst potential of Potassium than Sodium?

Answer 1

Even at rest, several potassium channels remain open (permeability of potassium is high), allowing potassium ions to stray in and out of them, thus bringing the membrane potential closer to its own Nernst potential

Question 2

What does membrane conductance depend on?

Answer 2

Membrane conductance highly depends on voltage and time; membrane capacitance is not much dependent on voltage and time

Question 3

What does membrane conductance refer to?

Answer 3

Membrane resistance (or its reverse, membrane conductance) refers to the ion permeation through cross-membrane proteins

Question 4

Give the characteristics of a membrane at rest

Answer 4

• Extracellular sodium concentration is greater than intracellular sodium concentration
• Extracellular chloride concentration is greater than intracellular chloride concentration
• Intracellular potassium concentration is greater than intracellular potassium concentration
• There is a net positive charge outside the membrane than inside.

Question 5

Why is there a net positive charge on the outside of the membrane when it is at rest?

Answer 5

This is because of:

• Net electrochemical gradient
• Potassium channels being open at rest, allowing potassium to leak, and thus potassium current equalizing

Question 6

What is the membrane potential at rest?

Answer 6

The membrane potential at rest is negative

Question 7

Describe depolarization and hyperpolarization

Answer 7

At rest, membrane potential is negative

• When the membrane potential gets more positive (goes towards zero), it is referred to as depolarization
• When membrane potential becomes more negative, it is called hyperpolarization

Question 8

Give the criteria for rectification

Answer 8

• If ratio of extra and intracellular concentrations is 1, the I-V curve is linear.
• Outward Rectification: If ratio of extra and intracellular concentrations is < (less than) 1, the I-V curve is non-linear. Slope increases with voltage.
• Inward Rectification: If ratio of extra and intracellular concentrations is > (greater than) 1, the I-V curve is also non-linear. Slope decreases with voltage