Psych Explained: Understanding Action Potential

Introduction

• Action potential: a brief electrical charge traveling down a neuron.
• Also known as neural impulse, nerve impulse, or spark.
• Enables neuron communication.

Memory Technique: Salty Banana

• Salty Banana: A memory aid.
  • Potassium (K⁺) inside the neuron.
  • Sodium (Na⁺) outside the neuron, like salt on a banana.

Neuron Structure

• Neuron Parts:
  • Soma/cell body: Central part.
  • Dendrites: Receive messages.
  • Axon: Carries action potential away from soma.
  • Axon terminal: Contains neurotransmitters.

Neuron Membrane and Ions

• Neuron is surrounded by ions: Sodium (Na⁺) and Potassium (K⁺).
  • Resting State:
    • K⁺ inside the neuron.
    • Na⁺ outside the neuron.
    • Inside charge: -70 millivolts (very negative).

Stimulating Neurons

• Stimulus example: Reaching for a glass of water.
  • Acetylcholine, a neurotransmitter, controls muscles.
  • Stimulus excites the neuron by binding acetylcholine to receptors.
  • Sodium channels open, allowing Na⁺ to enter, making neuron more positive.

Threshold and Action Potential

• Threshold: -55 millivolts.
  • Neuron fires if threshold is reached (All-or-none principle).
• Positive Feedback:
  • Sodium gates open along the axon, allowing more Na⁺ in, increasing positivity.
  • Charge rises from -55 to +30 millivolts.

Depolarization

• Depolarization: When the neuron's inside becomes more positive.
  • Na⁺ ions rush in, triggering the action potential.
  • Outside becomes negative as inside becomes positive.

Repolarization and Hyperpolarization

• Repolarization:
  • Neuron returns to resting state.
  • Sodium gates close, potassium gates open.
  • K⁺ flows out, making inside negative, down to -90 millivolts.
• Hyperpolarization (Refractory Period):
  • Neuron recharges, can't fire again immediately.
  • Returns to -70 millivolts (resting potential).

Final Summary

• Action Potential Phases:
  • Initial Resting State.
  • Threshold and Depolarization.
  • Repolarization and Hyperpolarization.
  • Return to Resting Potential, ready to fire again.