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C. Wenger:
"Analysis of the cluster functions in the human cochlea";
Supervisor: F. Rattay; E101, 2008; final examination: 2008-10.

Although the somatic region of afferent human cochlear neurons is quite unique, our contemporary knowledge on the neural coding principles in mammalian cochlear neurons is primarily based on animal experiments. Firstly many of the cochlear neurons are gathered to clusters with 2-4 (Tylstedt et al. 1997) neurons having a common insulation by myelin. Secondly 94% of human spiral ganglion cells are mostly surrounded by only one to several layers of satellite cells (Ota and Kimura 1980), whereas in cats 95% of spiral ganglion cells are firmly myelinated (Spoendlin 1971), which represents almost a reverse proportion between man and cat.
Both human particularities are expected to affect essentially the neural pattern resulting in a specifc human physiologic hearing performance. For example, Tylstedt and Rask-Andersen (2001) speculate whether unique formations between human spiral ganglion cells, which have not been observed in other species, may constitute interactive electrotonic or ephaptic transmission pathways.
Two mathematical models are presented to account for the morphological differences which are of major relevance for the propagation of an action potential. The first model was used to simulate the nonmyelinated soma region of human cochlear neurons. The results revealed a strong effect on the excitation pattern of the neuron after small changes in certain sensitive geometrical and electrical parameters. Furthermore an extended mathematical model including the human neuron cluster was developed. With this initial approach, the performed computer simulations for the theoretical case of a single neuron in addition to multiple neuron clusters demonstrated the influence of the cluster on the spiking behavior of the enclosed cochlear neurons.