īetween the hilus and the granule cell layer is a region called the subgranular zone which is a site of adult neurogenesis. Ī second excitatory cell type in the hilus is the mossy cell, that projects its axons widely along the septotemporal axis, (running from the septal area to the temporal lobe) with the ipsilateral projection skipping the first 1–2 mm near the cell bodies, an unusual configuration, hypothesized to prepare a set of cell assemblies in CA3 for a data retrieval role, by randomizing their cell distribution. These hilar dendrites are shorter and thinner, and have fewer side branches. Some of the basal dendrites of the granule cells curve up into the molecular layer. The granule cells are tightly packed together in a laminated manner that dampens the excitability of neurons. The granule cells of the granule layer project their axons known as mossy fibers to make excitatory synapses on the dendrites of CA3 pyramidal neurons. The granule layer is between the overlying molecular layer and the underlying hilus (polymorphic layer). The polymorphic layer is also the hilus of the dentate gyrus, (CA4, the junction of the hippocampus and dentate gyrus). (In the hippocampus the outer layer is the molecular layer, the middle layer is the pyramidal layer, and the inner layer the stratum oriens). The dentate gyrus, like the hippocampus, consists of three distinct layers: an outer molecular layer, a middle granule cell layer, and an inner polymorphic layer. Location of the dentate gyrus and relations to other structures.
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