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Table 3 Summary of Extracellular Field Types Far From An Axon

From: Classification of the extracellular fields produced by activated neural structures

Field Type Causes Far-Field Behavior Angular Generator Type Comment
Radiation Change in Dipole Direction Moving Dipole Through Region of Altered Electrical Properties cos(θ) -Free Particle. Complex Angular Dependence for Transition Radiation Traveling Clinically Insignificant
Dipole Change in Axon Radius (Dipole Tangent To Axon) cos(θ) Stationary Includes "Sealed End" Axons
  Axon curvature (Dipole Normal To Axon) cos(θ) Stationary  
  Localized Changes in Extracellular Electrical Properties Cos(θ) Stationary Only When Cylindrical Symmetry is Broken
Quadrupolar Impulse Travelling Along Uniform, Straight, Homogenous Axon in Isotropic Electrical Environment. 3 cos2(θ)-1 Travelling  
  Changes in Cable Properties.   3 cos2(θ)-1 Stationary  
  Localized Changes in Extracellular Electrical Properties   3 cos2(θ)-1 Stationary For Instance the Plane Conducting Boundary
Boundary Fields Generated Because of the Finite Volume In Which The Generator is Immersed Broadly Distributed Depends Critically on Boundary Shape and Size Stationary or Travelling Potentials Linear Far From Source For A Cylindrical Volume Conductor