Voltage-dependent ion channels mediate action potentials in excitable membranes, and play an important role in signal generation and propagation in neurons. In different neurons and different parts of neurons, voltage-dependent ion channels are distributed heterogeneously to facilitate specific functions. In my dissertation, I focus on myelinated axons and unmyelinated axons, use deterministic HH equations, stochastic HH equations and cable equations to investigate the effect of the spatial organization of ion channels on neuronal function.
The spiking behavior of a small cluster of ion channels triggered by intrinsic noise and synaptic noise was investigated using stochastic HH equations. The mechanism in neuronal spike-generation by small and large ion channel clusters is different. For large ion channel clusters, action potentials are elicited by synaptic noise. In small ion channel clusters, channel noise dominates over synaptic noise. Action potentials are generated at a frequency that is determined by single-channel kinetics.
In some cases, ion channels are distributed in clusters along unmyelinated axons. Each ion channel cluster spikes spontaneously. The synchronization of ion channel clusters along unmyelinated axons was investigated. It has been shown that two ion channel clusters exhibit maximal synchrony when they have the same size. Furthermore there is an optimal size of ion channel clusters with maximal synchrony.
Blockage of internodal potassium channels of the immature axon will induce sustained oscillation activity by a single stimulus. The mechanism underlying the oscillation activity and the function of internodal potassium channels were investigated. While the leakage current has no effect on axonal oscillations, increasing internodal sodium conductance as well as increasing internodal membrane capacitance can induce axonal oscillations. One function of internodal potassium channels is to stabilize the paranodal axolemma against nodal back-firing after a single impulse.
Experiments show that in some unmyelinated axons, ion channels are located in cluster. The effect of clustered ion channels on action potential propagation efficiency and speed was investigated. It has been shown that potassium channel localization is beneficial for increasing propagation efficiency and propagation speed of action potentials. Localization of sodium channels is advantageous to propagation efficiency only when axonal parameters are in a specific range.
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Channel / synaptic noise, Hodgkin-huxcey equations, Ion channels, Myelinated / unmyelinated axon, Synchronization|
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