Lecture 5

Question 1

What is equilibrium potential?

Answer 1

• membrane potential with no net movement of ions
• EP is equal to the Reverse potential

Question 2

What is the Reverse potential?

Answer 2

• Membrane potential at which ions change direction through the channel
• where the I-V curve crosses the X-axis

Question 3

As the electrical gradient shifts what happens to the ion flow?

Answer 3

• flow slows down as it reaches its equilibrium potential or reverse potential

Question 4

what is the resting membrane potential range?

Answer 4

-65 to -75 mV

Question 5

Is the Nernst Equation concentration dependent?

Answer 5

YES
- at 20 degrees celcius, (RT/ZF) is roughly equal to 25mV
- Multiply that by the ln of (conc. outside)/(conc. inside)

Question 6

How is the voltage of a neuron’s membrane measured?

Answer 6

• Voltage is measured for the inside of the neuron relative to the outside of the neuron by convention

Question 7

When the neuron is not firing, what happens?

Answer 7

• maintains a negative resting membrane potential (Vm) compared with its extracellular space

Question 8

Why were squid axons the best model to observe action potentials?

Answer 8

• Axon is visible to the naked eye
• Large in diameter
• Internal and external ion compositions can be controlled

Question 9

What would happen to the membrane if it was only permeable to K+?

Answer 9

• membrane potential would sit at around -93mV instead of -65 to -70 mV

Question 10

What percentage of permeability is Na+ compared to K+?

Answer 10

• Na+ is less than 10% permeable ot Na+ compared to K+

Question 11

How is the current for an ion determined?

Answer 11

• Determined by the difference between the membrane potential and the equilibrium potential for that ion
• I(k) = [Vm - Ek] (driving force)
  I(k) = current or flow of K+ ions

Question 12

Why is the Nernst equation not an accurate representation of actual membrane potential?

Answer 12

The Nernst equation only takes one ion species into account

Question 13

What does the constant field equation tell us?

Answer 13

The Goldman equation tells us that Vm depends on the relative permeabilities of the membrane to ions AND the equilibrium potential of those ions

Question 14

At rest, which ions flow in which direction?

Answer 14

• Na+ and Cl- flow in
• K+ flows out

Question 15

What are the five factors that determine the voltage of the membrane?

Answer 15

• Equlibrium potential of K+
• Equilibrium potential of Na+
• Conductances of Na+
• Conductance of K+
• Pump ratios

Question 16

which ion has relatively little effect on the Vm?

Answer 16

• Cl-

Question 17

What happens if the Vm becomes more positive without affecting the conc.?

Answer 17

• K+ no longer in chemical equilibrium
• More Positive Vm, K+ ions will move out of the cell

Question 18

What happens if the Vm becomes more negative?

Answer 18

• Negative Vm attracts positive charges of the K+
• More K+ will flow into the cell