Action Potential Explained

Introduction

• Memory Technique: Think of a salty banana.
• Refers to a brief electrical charge traveling down a neuron (axon).
• Terminology: Also called neural impulse, nerve impulse, or spark.
• Function: Allows neurons to communicate and transmit messages.

Neuron Structure Recap

• Parts of a Neuron: Soma (cell body), Dendrites, Axon, Axon terminal.
• Dendrites: Receive messages from sending neurons.
• Axon: Conducts the action potential away from the soma.
• Axon Terminal: Contains neurotransmitters.
• Membrane: Encloses the neuron, regulates the entry and exit of particles through channels.

Essential Ions

• Ions: Charged particles or molecules (positive or negative).
• Key Ions: Sodium (Na+), Potassium (K+).
• Salty Banana Memory Technique:
  • Inside: Potassium (K+)
  • Outside: Sodium (Na+)
  • Salt on Banana analogy helps remember concentrations of these ions when neuron is at rest.

Resting Potential

• Resting State: Neuron is at -70 millivolts (very negative inside).
• Negative Charge: Due to ions distribution (K+ inside, Na+ outside).

Exciting the Neuron

• Stimulus: Can be anything (e.g., reaching for a glass of water).
• Neurotransmitter: Example - Acetylcholine which controls muscle movement.
• Process:
  1. Stimulus induces neurotransmitters to bind to receptor sites on dendrites.
  2. Channels Open: Sodium (Na+) rushes in, making inside more positive.
  3. Threshold: If inside reaches -55 millivolts, action potential fires (all-or-none principle).

Depolarization

• Voltage Change: Inside becomes more positive due to sodium influx.
• Threshold Reached: Voltage changes dramatically from -55 to +30 millivolts.
• Depolarization: The cell becoming more positive inside (Na+ entering).

Repolarization

• Returning to Negative: Sodium gates close, potassium gates open.
• Potassium Out: Positively charged potassium (K+) rushes out.
• Voltage: Returns to negative but briefly overshoots to -90 millivolts.
• Hyperpolarized/ Refractory Period: Neuron can't fire again immediately as it recharges.

Resting Potential Restored

• Voltage: Returns to normal resting potential of -70 millivolts.
• Polarized State Restored: Negative inside and positive outside restored.
• Ready to Fire Again: Neuron can respond to new stimuli.