Action Potential: A Brief Overview

Introduction

• Action potential: A momentary reversal of membrane potential.
• Basis for electrical signaling within neurons.

Membrane Potential

• Resting membrane potential: ~-70 millivolts.
• Depolarization: Membrane potential becomes less negative.
• Threshold membrane potential: ~-55 millivolts for neurons at rest.

Phases of Action Potential

Rising Phase

• Triggered when threshold is reached.
• Sodium channels open.
  • Sodium ions (Na⁺) flow into the cell.
  • Causes massive depolarization.
  • Membrane potential becomes positive.

Falling Phase

• Sodium channels close.
• Potassium channels open.
  • Potassium ions (K⁺) flow out of the cell.
  • Promotes repolarization.
  • Membrane returns to resting potential.
  • Overshoot causes hyperpolarization.

Refractory Period

• Time during which neuron is hyperpolarized.
• Difficult to initiate another action potential.

Signal Propagation

• The action potential travels down the neuron.
• Can cause release of neurotransmitter at axon terminals.
• Passes the signal to the next neuron.

Conclusion

• The action potential is crucial for neuron communication.
• Involves a sequence of voltage changes across the neuron's membrane.