PEx 3 Activity 1

Review Sheet Results
1. Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels.
Your answer:
Because outside a typical cell, the concentration of K+ is about 5mM and the concentration of Na+ is about 150 mM. When you increase the concentration of K+ from 5 to 25 mM and reduce concentration of Na+ from 150 to 130 mM, the outside has more concentration of K+. The membrane is permeable to a particular ion, that ion will diffuse down its concentration gradient from a region of higher concentration to a region of lower concentration.
2. Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value. How well did the results compare with your prediction?
Your answer:
Because outside has more K+, the rate of diffusion is less. The resting membrane potential will become less negative.
3. Explain why a change in extracellular Na+ did not significantly alter the membrane potential in the resting neuron? Your answer:
Because it did not effect the resting membrane potential.
4. Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.
Your answer:
The resting membrane potential is really a potential difference between the inside of the cell (intracellular) and the outside of the cell (extracellular) across the resting permeability of the membrane to ions and on the intracellular and extracellular concentraions of those ions to which the membrane is permeable. Na+ and K+ are the most important ions, and the concentrations of these ions are established by transport protein, such as the Na+ -K+ pump, so that the intracellular Na+ concentration is low and the intracellular K+ concentraion is high. The ions will diffuse down its concentration gradient from a region of higher concentration to a region of lower concentration.
5. Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
Your answer:
The resting period potential is a potential difference between the inside of the cell and the outside of the cell across the membrane. It depends on the resting permeability of the membrane to ions and on the intracellular and extracellular concentrations of those ions to which the membrane is permeable.