Deep Nuclei












Deep Nuclei

Now that we know something about the inputs to the Purkinje cells, let's look at the distribution of their axons. Purkinje cells in the four different zones, MEDIAL, INTERMEDIATE, LATERAL AND FLOCCULONODULAR, project to different deep cerebellar nuclei. Three of the four deep cerebellar nuclei can be seen below in an old friend from the brain stem, level 5. You have not seen the dorsal part of this section before, but it shows three of the four sets of deep cerebellar nuclei. The most lateral deep cerebellar nucleus, the dentate, receives its Purkinje cell input from the lateral zone of the cerebellum. Remember that this lateral zone of the cerebellum receives its input from olivocerebellar and pontocerebellar fibers carrying planning information from the posterior parietal area. The interpositus nucleus (globose and emboliform) receives its Purkinje cell input from the intermediate zone of the cerebellum. The intermediate zone of the cerebellum receives its input from olivocerebellar and pontocerebellar fibers carrying information from primary motor cortex (area 4) AND from the DSCT and CCT. The Purkinje cells that innervate the medially located fastigial nucleus lie in the medial zone of the cerebellum which, as you remember, receives input from the DSCT and CCT (and the olive!).

Purkinje cells in the flocculonodular zone (or lobe) also need a deep nucleus. Gee, where is it? Well, the Purkinje cells of the flocculonodular lobe terminate in the VESTIBULAR NUCLEI, which we can consider as a "surrogate" deep cerebellar nucleus. These Purkinje cells that are destined for the vestibular nuclei travel in the inferior cerebellar peduncle (along with the fibers from the vestibular nerve and nuclei that are entering the cerebellum.)

The signals from the Purkinje cells that terminate in the deep cerebellar nuclei are inhibitory. Think of the inhibitory signal as increasing or decreasing depending upon what is happening in the cerebellum. Also remember that the deep cerebellar nuclei also receive EXCITATORY inputs from the collaterals of both mossy and climbing fibers as they pass through the deep white matter on their way to the overlying cerebellar cortex. The interplay of the inhibitory (Purkinje cell) and excitatory (mossy and climbing fiber) inputs to the deep nuclei determines their output signal to the other parts of the brain that we will discuss next.