Lecture Notes: Neuron Action Potentials and Nervous System Function

Overview

• Neurons communicate via electrical impulses akin to a simple app sending signals.
• Neurons send uniform impulses, varying only in frequency.
• The brain interprets these signals, recognizing different sensations and actions.

Concept of Action Potential

• Action Potential: The key impulse responsible for actions, thoughts, and emotions.
• Neurons fire electrical signals (action potentials) down their axons to neighboring neurons.
• Signals are uniform but vary in frequency and are decoded by the brain.

Electricity Basics in the Nervous System

• Body as a Battery: Electrically neutral overall but with localized charge differences.
• Membrane Potential: Voltage difference across the cell membrane due to separated charges.
• Voltage: Measure of potential energy created by separated charges.
• Current: Flow of electricity (ions) across cell membranes.
• Resistance: Insulators (high resistance) vs. Conductors (low resistance) in the flow of current.

Resting Neuron and Membrane Potential

• Resting Membrane Potential: Neuron's inside more negative than outside (~-70 mV).
• Sodium-Potassium Pump: Maintains charge gradient by pumping ions in and out.
• Polarization: Negative membrane potential when neuron is at rest.

Ion Channels and Their Roles

• Ion Channels: Pathways for ions to move across membranes.
  • Voltage-Gated Channels: Triggered by changes in membrane potential.
  • Ligand-Gated Channels: Open when specific neurotransmitters bind.
  • Mechanically-Gated Channels: Respond to physical membrane changes.
• Gradient Drive: Ions move to balance concentrations and charges.

Action Potential Generation

• Stimulus: Environmental changes can trigger ion channel opening.
• Threshold: Action potential requires a charge change to ~-55 mV (all-or-nothing response).
• Depolarization: Influx of sodium ions makes internal membrane potential positive (~40 mV).
• Repolarization: Potassium ions exit to restore negative charge (overshoots to hyperpolarization).
• Refractory Period: Temporary unresponsiveness to prevent backward signal transmission.

Action Potential Properties

• Signal Strength: Uniform strength; varies only in frequency.
• Signal Frequency: Intensity of stimulus or action reflected in frequency.
• Conduction Velocity: Influenced by myelin sheath and axon characteristics.
  • Myelinated Axons: Faster signal transmission (saltatory conduction via nodes of Ranvier).

Conclusion

• The nervous system's uniform voltage signaling is a fundamental communication method.
• Future Topic: What happens when an action potential reaches the end of an axon.
• Supplementary Info: Introduction to Crash Course Kids for younger audiences, focusing on educational content for children.