Lecture Notes: Resting Membrane Potential and Action Potential
Resting Membrane Potential
- Definition: A state where the axon's membrane potential is stable and ready to conduct nerve impulses.
- Creation:
- Sodium-Potassium Pump: Uses ATP for active transport.
- Transports 3 sodium ions (Na+) out and 2 potassium ions (K+) in against their concentration gradients.
- Results in a more negative charge inside the axon due to negatively charged proteins.
- Resting Membrane Potential Value: Approximately -70 mV (may vary by species).
Action Potential
- Two Stages: Depolarization and Repolarization.
- Depolarization:
- Process:
- Stimulus causes voltage-gated sodium ion channels to open.
- Sodium ions rush into the axon down the concentration gradient (higher concentration outside to lower inside).
- Membrane potential changes from -70 mV to +30 mV.
- Key Points:
- The inside of the axon becomes positive relative to the outside.
- Voltage-gated sodium ion channels close at +30 mV.
Repolarization
- Process:
- Voltage-gated potassium ion channels open at +30 mV.
- Potassium ions rush out of the axon (high concentration inside to low outside).
- Causes the inside to become more negative again.
- Key Points:
- Membrane potential overshoots, becoming more negative than -70 mV (around -80 mV).
- Voltage-gated potassium ion channels close after overshooting.
Summary of Action Potential
- Action Potential: A rapid change in membrane potential involving depolarization and repolarization.
- Function: Allows nerve impulses to be sent along the axon by altering the charge across the axon membrane.
Conclusion
- Understanding the Process:
- The axon needs a resting membrane potential to conduct impulses.
- Depolarization and repolarization are essential for the action potential.
- This cycle allows the transmission of nerve signals effectively.
These notes highlight the mechanisms of resting membrane potential and action potential, which are crucial for nerve impulse conduction.