The graincell axon runs more or less straight up through the grain cell and Purkinje cell layers and out into the molecular layer. Here, at different distances from the surface, the axon divides T-shaped and forms a 5-10 mm long, 0.5-2 μm thick, so-called parallel wire. The parallel wires run transversely in the frontal plane, perpendicular to the longitudinal axis of the brain, piercing the flattened dendrite trees of the Purkinje cells . A parallel wire contacts with excitatory dendritic tagsynapses 2000-4000, successively lined up, Purkinje cells. A Purkinje cell, in turn, is contacted by approx. 300,000 (three hundred thousand) different grain cells!
The parallel wires also pass through and excite the dendrite trees of the basket, star and Golgi cells.