Neuroscience: Resting Membrane Potential & Action Potential

Study Notes

The RMP is the difference in potential across the cell membrane, usually around -70mV in neurons
Caused by a combination of factors:
- Potassium efflux: Potassium ions are more permeable and move out of the cell, making the inside more negative.
- Sodium-potassium pump: Actively pumps 3 sodium ions out of the cell for every 2 potassium ions pumped in, contributing to the negative charge inside.
- Non-diffusible anions: Negatively charged molecules within the cell that can't cross the membrane, contributing to the negative charge.
RMP magnitude varies between cells:
- Skeletal and cardiac muscles: -90mV
- Nerve cells: -70mV
The Goldman-Hodgkin-Katz equation calculates RMP based on ion concentrations and permeabilities.

Characterized by rapid changes in membrane potential in excitable tissues like muscles and nerves.
Components:
- Polarization: Resting state where the inside is negative compared to the outside.
- Depolarization: Inside becomes more positive than the outside due to sodium influx.
- Repolarization: Inside becomes more negative than the outside due to potassium efflux, returning towards RMP.

Voltage-gated sodium and potassium channels are responsible for the action potential events:
- Threshold potential: The depolarization level that triggers opening of both sodium and potassium channels.
- Fast sodium channels: Open rapidly and close quickly, allowing rapid sodium influx.
- Slower potassium channels: Open slowly and close with a delay, allowing potassium efflux.

Potassium channels open, allowing potassium efflux.
Potassium leaves the cell, making the inside more negative and causing repolarization.

Slow closing of potassium channels leads to hyperpolarization because potassium continues to leave the cell.
The membrane gradually returns to RMP as potassium permeability returns to normal.

The Na+/K+ ATPase pump doesn't play a role in depolarization, repolarization, or returning to RMP.
However, it maintains ion concentration gradients that are essential for the action potential:
- Sodium influx during depolarization increases intracellular sodium.
- Potassium efflux during repolarization decreases intracellular potassium.
- The Na+/K+ ATPase pump restores these ions to their normal intracellular concentrations, ensuring the action potential can happen repeatedly.