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 |
| Â | Axon curvature (Dipole Normal To Axon) |
| cos(θ) | Stationary |  |
| Â | 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 |
