These axons pass through the pons and enter the cerebellum where they form synapses with the deep cerebellar nuclei and Purkinje cells. Each climbing fiber will form synapses with 1-10 Purkinje cells.
Early in development, Purkinje cells are innervated by multiple climbing fibers, but as the cerebellum matures, these inputs gradually become eliminated resulting in a single climbing fiber input per Purkinje cell.
These fibers provide very powerful, excitatory input to the cerebellum which results in the generation of complex spikes in Purkinje cells.
Climbing fiber activation is thought to serve as a motor error signal sent to the cerebellum, and is an important signal for motor timing.