Nerve Impulses and Action Potentials

Overview

• Nerve impulses are electrical signals traveling along neurons.
• Not typical electricity (electron flow); involves movement of charged particles (ions) across cell membranes.

Key Concepts

Resting State

• Sodium Ions: High concentration outside the neuron.
• Potassium Ions: High concentration inside the neuron's cytosol.
• Charge: Overall negative internal charge (-70 mV) due to ion distribution.
• Channels: Sodium and potassium channels are gated and closed.

Depolarization

• Begins the nerve impulse.
• Sodium Channels Open: Sodium rushes into the cell.
• Charge Shift: Inside becomes more positive, outside more negative.
• Sodium Gates Close.

Repolarization

• Potassium Channels Open: Potassium flows out of the cell.
• Restores negative internal charge relative to the external environment.
• Potassium Gates Close.

Refractory Period

• Neuron cannot immediately fire another impulse.
• Sodium-Potassium Pump: Uses ATP to move ions back to their resting potential positions (3 sodium out, 2 potassium in).
• Essential for ion movement down electrochemical gradients.

Action Potentials

• Direction: Only move in one direction (dendrites to axon terminals).
• Local Current: Flow of sodium through gates triggers successive action potentials.
• Threshold Potential: -55 mV needed to trigger an action potential.

Hyperpolarization

• Sometimes, the cell becomes more negative than -70 mV.
• Corrected during the refractory period by the sodium-potassium pump.

Importance

• The brain uses significant energy for the sodium-potassium pump processes.
• Action potentials are waves of ions moving in a pattern essential for nerve impulse transmission.

"Thanks for watching this episode of Teacher's Pet!" (Note: Final credits from the lecture to remind of the program's source)