Neurophysiology Study Guide
Neurophysiology Study Guide 1. Define "equilibrium potential". Why is the resting potential closer to the potassium equilibrium potential (EK+) than the sodium potential (ENa+)?
The equilibrium potential is the point at which the force exerted on an ion by electrostatic and concentration gradient forces are balanced, and there is no net movement of that ion. The resting potential is closer to EK+ than ENa+ because the cell membrane is more permeable to potassium than sodium. 2. How would ENa+ change following an increase in the external concentration of sodium? Would the resting potential be affected significantly? If the external concentration of sodium was increased, the concentration gradient driving the movement of sodium would be increased more sodium would diffuse into the cell and would reduce some of the negative charge on the inner surface of the lipid bilayer. This would serve to decrease (make less negative) the resting potential, but would not affect it significantly since the membrane is much more permeable to K.
3. Does any net Ionic current flow at the resting potential? What are the relationships among “passive" and “pump”ionic currents at the resting potential?
There is no net ionic current flow at the resting potential. However, since neither Na+ nor K+ is at equilibrium, there is a net flow of each across the membrane. The Na-K pump generates the concentration difference that sustains the resting potential: but it is the passive ionic flow that creates the resting potential. Pump currents balance passive currents (diffusion) at the resting potential.
3. Define "electrogenic" and "neutral” pumps. What role does the Na-K pump play in the resting potential?
An electrogenic pump creates a potential difference across the membrane - positive and negative charges are not transported across the membrane in equal amounts.
The equilibrium potential is the point at which the force exerted on an ion by electrostatic and concentration gradient forces are balanced, and there is no net movement of that ion. The resting potential is closer to EK+ than ENa+ because the cell membrane is more permeable to potassium than sodium. 2. How would ENa+ change following an increase in the external concentration of sodium? Would the resting potential be affected significantly? If the external concentration of sodium was increased, the concentration gradient driving the movement of sodium would be increased more sodium would diffuse into the cell and would reduce some of the negative charge on the inner surface of the lipid bilayer. This would serve to decrease (make less negative) the resting potential, but would not affect it significantly since the membrane is much more permeable to K.
3. Does any net Ionic current flow at the resting potential? What are the relationships among “passive" and “pump”ionic currents at the resting potential?
There is no net ionic current flow at the resting potential. However, since neither Na+ nor K+ is at equilibrium, there is a net flow of each across the membrane. The Na-K pump generates the concentration difference that sustains the resting potential: but it is the passive ionic flow that creates the resting potential. Pump currents balance passive currents (diffusion) at the resting potential.
3. Define "electrogenic" and "neutral” pumps. What role does the Na-K pump play in the resting potential?
An electrogenic pump creates a potential difference across the membrane - positive and negative charges are not transported across the membrane in equal amounts.