There are two lines of input to the cerebellar cortex and they are excitatory to the Purkinje cells: the climbing fibers and the mossy fibers. The climbing fibres are the terminal fibers of the olivocerebellar tracts. They make synaptic contacts with Purkinje cells and cerebellar nuclei. Each climbing fiber contacts one to ten Purkinje cells and each of it receives input from one single Climbing fiber. They are involved in the learning process and correct mismatches between intended and actual movement. The mossy fibers are the terminal fibers of all other cerebellar afferent tracts. They have a diffuse excitatory effect stimulating thousands of Purkinje cells through the granule cells). Each Purkinje cell receives input from approximately 200.000 granular cells and each granular cell receives input from many mossy fibers.
Phylogenetical and lobular divisions of the cerebellum are closely related to its input. The cerebrocerebellum receives corticopontine tracts through mossy fibers from somatosensory, motor, visual and cognitive areas (for visual spatial organization and memory). The spinocerebellum receives spinocerebellar tracts through mossy fibers and from brain stem nuclei through climbing fibers (for keeping muscle tone). The vestibulocerebellum receives vestibular tracts through mossy fibers and from optokinetic centers in the brain stem through climbing fibers.
 These are ipsilateral afferent fibers from the spinal cord through the dorsal spinocerebellar, the ventral spinocerebellar, the rostral spinocerebellar tracts, and from the lateral cuneate nucleus.