Graduation Year

2017

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Salvatore D. Morgera, Ph.D.

Committee Member

Wilfrido Moreno, Ph.D.

Committee Member

Ghanim Ullah, Ph.D.

Committee Member

Mark Jaroszeski, Ph.D.

Committee Member

Arthur D. Snider, Ph.D.

Keywords

synchronization, coupling, ephaptic, neurons, bioelectricity

Abstract

In this dissertation, we investigate coupling between axons in a tract, when the tract has an arbitrary cross-section, with the coupling being mediated by currents as well as electric fields. Under the current mediated setting, we develop a new master equation which captures the relative axonal geometry, specifically, the axon inclinations θi and the inter-axon distances Wip and perform a number of simulations. We observe synchronization in our simulations of axons with differing diameters and separation-dependent coupling delays in the case of non-trivial tract geometries. For the field-mediated interaction setting, we determine the electric near-field of a firing axon’s node of Ranvier - its strength and direction - by a volume conduction approach as well as a more microscopic, dipole-based approach. We obtain field strengths of about 105V/m at a few hundred micron distance from the source at the node. With the field levels having been found significant enough to cause 100 mV voltage drops across 1 micron-diameter axons, we develop an alternate, field-mediated model for synchronization between axons based on the dipole fields generated during action potential propagation. This model shows that synchronization between action potentials on differing axons depends on the phases of the synchronizing action potentials and not merely their separation. Since synchronization takes place in both settings, but currents are generated by fields, when constrained to a specific direction, we find that the field picture is a generalization of the presently prevalent current mediated picture for interaction between axons.

Download

Share

COinS