Unipolar brush cells occur only in the granular layers of the cerebellum. They are excitatory with glutamate as a transmitter substance and are counted among the nerve cell types of the cerebellar cortex. The cell body of the brush cell is the size of a small Golgi neuron.
The unipolar brush cell emits a single short and thick dendritic stem that ends in a bristle/brush-like bundle of very thin and short protrusions, so-called dendrioles. The cell membrane of the dendriol bundle forms a coherent postsynaptic membrane section to which an excitatory moss filament connects with its end ends. The so formed synaptic complex is one of the largest observed in the nervous system of vertebrates.
The large volume of the very extensive synaptic cleft means that the amount of transmitter substance released when the moss filament sends in action potentials does not have time to disappear as quickly as in a normal - more limited - synaptic complex, but affects the postsynaptic membrane for a relatively long time; for 10s of milliseconds. The brush cell responds by delivering a lengthy intense series of action potentials.
The dendriol bundles of brush cells also receive inhibitory Golgi neurons end endings whose activity is thought to modulate the effect of a moss wire stimulus.
The axon of the brush cell is short. It divides into a pair of end branches that have moss wire appearance and moss wire characteristics. The end branches form typical moss wire end ends. These contact both nearby brush cells and grain cells.
The incidence of bristle cells is particularly high in the vestibulocerebellum.