Lecture Notes on Action Potentials and Ion Channels

Temporal and Spatial Summation

• Temporal Summation: Repeated signals over time that can lead to an action potential if threshold is reached.
• Spatial Summation: Involves different stimuli; can result in varied outcomes (e.g., combining excitatory and inhibitory signals).
• Hyperpolarization: Membrane potential becomes more negative.
• Depolarization: Membrane potential becomes less negative, moving closer to threshold.

Graded Potentials and Action Potentials

• Graded Potentials: Unable to communicate over long distances as they decay over time.
• Action Potential: Reaches threshold with sufficient graded potentials, enabling long-distance communication.

Ion Movement in Action Potentials

• Key Players: Sodium (Na+) and Potassium (K+).
• Resting Membrane Potential: Typically -70 mV.
• Depolarizing Events: Membrane potential becomes more positive.
• Repolarizing Events: Return to resting potential.
• Hyperpolarizing Events: Membrane potential becomes more negative.

Types of Ion Channels

• Leak Channels: Always open, maintain resting membrane potential.
• Ligand Gated Channels: Open/close in response to ligand binding.
• Voltage Gated Channels: Open/close in response to changes in membrane potential.

Phases of Action Potential

• Phase 1 (Depolarization): Sodium channels open; membrane potential rises.
• Phase 2 (Repolarization): Sodium channels close; potassium channels open, membrane potential decreases.
• Phase 3 (Hyperpolarization): Potassium channels remain open briefly, then close; membrane potential becomes more negative before returning to rest.

Sodium Channels

• Activation Gate: Opens at threshold.
• Inactivation Gate: Closes at peak of action potential (30 mV), stopping Na+ influx.

Potassium Channels

• Open at 30 mV, causing repolarization by allowing K+ to exit the cell.

Membrane Permeability Changes

• Phase 1: High sodium permeability.
• Phase 2: High potassium permeability.
• Phase 3: Potassium channels close, restoring resting potential.

Important Potentials

• Resting Potential: -70 mV.
• Threshold: -55 mV.
• Peak Potential: +30 mV.
• Equilibrium Potentials: Na+ (+60 mV), K+ (-94 mV).

Summary

• Graded potentials lead to action potentials if threshold is reached.
• Sodium and potassium channels regulate phases of action potentials.
• Action potentials allow for rapid communication across neurons.

Note: There was a clarification on slide content regarding sodium channel gates and the distinction between depolarization and repolarization processes.