Cluster of human spiral ganglion neurons : a computational model study of ephaptic coupling effects release_u7y7jfxcxnhixcoamktrh3x5g4

Abstract

Motivations of the thesis: Cochlear Implants are the medical option for people, who severe to profound hearing loss. Since my thesis related with human auditory system, considering the human auditory nerves is very important topic. Human auditory neurons show micro- anatomical peculiarities which dier considerably from other species, for instance human spiral ganglion neuron bodies are unmyelinated and often arranged in functional units covered by common satellite glial cells. Since human spiral ganglion cells are not experimentally accessible, theoretical analysis concerning single neuron response has to be performed. Nonetheless the physiology of hearing is not totally understood, e.g. speech recognition and perception in noisy environment, attenuation eects and the temporal ne structure of the neural pattern. Methods of the investigations: The anatomical data presented in the thesis are based on several human cochlea and compose the fundament of the subsequent computer simulations which provide an appropriate method for single cell analysis. The electrical activity of cochlear neurons can be deducted from solving systems of dierential equations which will enhance our understanding of action potential initiation and propagation of nerve impulses. A new model for simulating the natural spiking behavior of human cochlear neurons as well as their excitability to microstimulation by electrodes were presented in my thesis. Final results: Hierarchial cluster analysis of acquired volumetric data of unmyelinated human auditory cell somata indicates the existence of four distinct populations of auditory nerves within the human cochlea. The unmyelinated soma region reduces the safety factor of AP transmission whereas certain sensitive parameter can be identi ed leading to divergent excitation pro les. For successful ephaptic stimulation the spikes of adjacent neurons get synchronized. Some inhibiting eects can also be observed due to large current loss on the sensitive human soma region. Mathematical modeling and compute [...]
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