Understanding Action Potential Propagation

Oct 11, 2024

Lecture Notes: Propagation of Action Potentials

Introduction

  • Action Potential Propagation: Unlike graded potentials, action potentials are regenerated at each point along the axon, allowing them to maintain strength over distance.
  • All-or-None Law: Action potentials either occur fully or not at all, contributing to their consistent propagation.

Directionality of Action Potentials

  • Unidirectional Flow:
    • Action potentials move in one direction due to the refractory period, where the recently depolarized area cannot generate a new action potential.
    • This prevents reverse travel toward the soma and dendrites.
  • Backpropagation: While an action potential doesn’t typically travel backward to the soma and dendrites, these areas register the electrical event passively.

Mechanism of Action Potential Propagation

  • Local Currents: Depolarization from the action potential generates local currents that depolarize adjacent membrane sections.
  • Refractory Period: Ensures action potential moves in one direction as it prevents new action potentials from being initiated in the depolarized area.

Speed of Propagation

  • Variability in Speed:
    • Thinnest axons: ~1 meter/second
    • Large diameter axons: ~30 meters/second
  • Comparative Speeds: Humans have faster propagation than larger animals due to differences in axon size and myelination.

Role of Myelination

  • Myelin Sheath: Enhances speed by insulating parts of the axon.
  • Nodes of Ranvier: Action potentials jump from node to node via saltatory conduction, increasing speed significantly up to 120 meters/second.
    • Latin "saltare" means to jump.
  • Saltatory Conduction:
    • Occurs only at nodes of Ranvier where action potentials regenerate.
    • Conserves energy as sodium ions are required only at these nodes.

Conclusion

  • Key Concepts Covered: Resting potential, action potential, and propagation.
  • Further Reading: Encouragement to review the textbook for deeper understanding.

Visual Aids

  • Video and Picture Descriptions:
    • Video illustrates unidirectional propagation of action potentials.
    • Picture A shows myelinated axon structure and node of Ranvier interactions.

End of Lecture: Ensure comprehension by revisiting textbook materials. Thank you for your attention.