Overview
This lecture introduces the resting membrane potential, focusing on how ion gradients and membrane transporters establish the electrical conditions necessary for action potentials in neurons.
Resting Membrane Potential
- Resting membrane potential refers to the steady voltage across a cell's membrane when the cell is not actively transmitting signals.
- The sodium-potassium ATPase pump exchanges three sodium ions (Na⁺) out of the cell for two potassium ions (K⁺) into the cell.
- The pump requires ATP (cell energy) and converts it to ADP and inorganic phosphate during this process.
- Pumping out more positive ions than are brought in causes the outside of the cell to become positively charged relative to the inside.
- This results in a net negative charge inside the cell, creating an electrical potential difference (voltage) across the membrane.
- Some ions can leak through the membrane, allowing a steady state to be reached where the voltage remains constant.
- The typical resting membrane potential in neurons is approximately -70 millivolts (mV).
Ion Gradients and Concentrations
- There is a higher concentration of sodium ions outside the cell and a higher concentration of potassium ions inside the cell.
- Sodium ions want to move into the cell down their concentration gradient but are blocked by the membrane.
- Potassium ions want to move out of the cell down their concentration gradient but are also blocked by the membrane.
- These concentration gradients and the separation of charges across the membrane contribute to the resting membrane potential.
Membrane Voltage Recording
- Measuring voltage across the cell membrane over time shows a constant value during the resting state.
- This stable voltage is different from what occurs during an action potential, which will be discussed later.
Key Terms & Definitions
- Resting membrane potential — the steady voltage across a cell's membrane when the cell is inactive, usually around -70 mV in neurons.
- Sodium-potassium ATPase — a membrane protein that uses ATP to pump 3 Na⁺ out and 2 K⁺ into the cell.
- ATP (Adenosine Triphosphate) — the main energy source for cellular processes.
- Concentration gradient — the difference in ion concentration across the cell membrane.
Action Items / Next Steps
- Review upcoming material on voltage-gated ion channels and action potentials.
- Access the PDF or additional tutorials at the mentioned website.