Notes on Action Potentials and Neuronal Communication

Introduction

• Concept of communicating thoughts and feelings with a simple app analogy.
• Neurons send impulses responsible for actions, thoughts, and emotions via electrical signals.

Action Potential

• Definition: The nerve impulse sent by a neuron.
• Characteristic: Neurons transmit signals in one uniform strength and speed but vary the frequency (pulses).
• Signals organized by the brain: location, sensation, magnitude, importance.
• Action potentials are fundamental in anatomy, physiology, and life itself.

Basic Principles of Electricity

• Body as a sack of batteries:
  • Electrostatically neutral with positive and negative charges.
  • Requires barriers (membranes) to keep charges separated until needed.
• Voltage:
  • The measure of potential energy from separated charges, expressed as millivolts in the body.
  • Resting Membrane Potential: -70 mV when neuron is at rest.
  • More sodium ions (positive) outside than potassium ions (positive) inside, leading to an overall negative interior charge.
  • Neuron is polarized at rest.

Sodium-Potassium Pump

• Critical component in maintaining charge separation:
  • Pumps 3 sodium ions out for every 2 potassium ions in.
  • Creates an electrochemical gradient (nature favors balance).

Ion Channels

• Types of Ion Channels:
  • Voltage-gated channels: Open at specific membrane potentials (e.g., sodium channels around -55 mV).
  • Ligand-gated channels: Open upon binding of specific neurotransmitters.
  • Mechanically gated channels: Open in response to physical deformation (e.g., stretching).

Graded Potentials vs. Action Potentials

• Graded Potential:
  • Small, localized changes in membrane potential.
• Action Potential:
  • Large changes in membrane potential that are all-or-nothing.
  • Triggered when the change crosses a threshold of -55 mV.

Steps of Action Potential

1. Resting State: All channels closed at -70 mV.
2. Depolarization:
   • Stimulus opens sodium channels.
   • Sodium rushes into the neuron, causing depolarization.
   • Peaks around +40 mV.
3. Repolarization:
   • Voltage-gated potassium channels open, potassium exits.
   • Cell attempts to balance charges; may lead to hyperpolarization (around -75 mV).
4. Refractory Period:
   • No new signals can be sent; prevents dual direction travel of signals.

Signaling Characteristics

• Frequency of Action Potentials:
  • Weak stimuli = lower frequency buzz
  • Strong stimuli = higher frequency buzz
• Conduction Velocity:
  • Faster in myelinated axons via saltatory conduction (jumping between Nodes of Ranvier).

Conclusion

• Neurons communicate in a single-tone buzz regardless of the stimulus intensity.
• Review of how electrical changes convert into action potentials for signaling between neurons.

Final Notes

• Mention of new initiative: Crash Course Kids:
  • Hosted by Sabrina Cruz focusing on accessible science content for younger audiences.
  • Plans to cover various topics relevant to younger students.