Overview of Action Potential

Introduction

• Action Potential: Momentary reversal of membrane potential, crucial for electrical signaling within neurons.
• Membrane Potential: Essential concept linked to action potential.
  • Resting Membrane Potential: Typically around -70 millivolts in neurons.

Key Stages of Action Potential

Depolarization

• Triggered when neurotransmitters bind to receptors on neuron dendrites.
• Causes membrane potential to become less negative, moving closer to 0 (depolarization).
• When repeated depolarization occurs, the neuron reaches the threshold membrane potential.
  • For a neuron with -70 mV, threshold is around -55 mV.

Rising Phase

• Sodium Channels Open: Large influx of positively charged sodium ions into the cell.
• Massive depolarization occurs as membrane potential hits 0, then becomes positive.
• Action Potential Signal: Created as an electrical signal traveling down the neuron.

Falling Phase

• Peak of Action Potential: Sodium channels close, potassium channels open.
• Potassium ions exit the cell, promoting repolarization.
• Membrane potential returns towards the resting level but overshoots, causing hyperpolarization.

Refractory Period

• During hyperpolarization, neuron becomes less excitable.
• Refractory Period: Difficult to stimulate neuron to fire another action potential.
• Eventually, potassium channels close, restoring the resting membrane potential.

Conclusion

• The action potential enables the transmission of electrical signals down the neuron.
• Causes neurotransmitter release at axon terminals, passing the signal to subsequent neurons.