Unipolar brush cells possess a single dendrite that ends in a cluster of branchlets resembling a brush. These cells receive stimulation from mossy fibers and inhibition from Golgi cells. It is believed that they form synapses with granule and Golgi cells, thus serving as an excitatory link in the mossy fiber-parallel fiber pathway.

Candelabrum cells, found in the Purkinje layer, are GABAergic cells with dendrites and axons that terminate in the molecular layer, forming a candelabrum-like arborization pattern.

The cerebellar nuclei are the primary targets of the cerebellar cortex. This projection follows a topographical organization, with each longitudinal strip of cortex targeting a specific region of the cerebellar nuclei. Generally, the vermis projects to the fastigial and vestibular nuclei, the paravermal region projects to the interpositus, and the lateral hemisphere projects to the dentate nucleus.

Subsequently, the cerebellar nuclear neurons relay the output from the cerebellum to the rest of the brain, except for the Purkinje cells which project to the vestibular nuclei. It is helpful to categorize the nuclear cells based on whether they are GABAergic since the GABAergic cells project back to the inferior olivary nucleus, forming a negative-feedback loop with one of the cerebellum's principal afferent sources. Importantly, GABAergic cells project to the specific part of the inferior olivary nucleus from which they receive input, and which their overlying longitudinal strip of cortex receives climbing fibers. This functional organization forms a series of closed loops between the cerebellar cortex, cerebellar nuclei, and inferior olivary nucleus. The non-GABAergic, excitatory nuclear cells project to various targets ranging from the spinal cord to the thalamus. Generally, each nucleus generates crossed ascending and descending projections that exit the cerebellum via the superior cerebellar peduncle. The fastigial nucleus also gives rise to significant uncrossed fibers and a second crossed projection known as the uncinate gyrus or hook bundle, which exits via the inferior cerebellar peduncle.

While there are differences in the specific targets of each nucleus, the ascending cerebellar projections generally target midbrain structures like the red nucleus and superior colliculus, as well as the ventral lateral nucleus of the thalamus that connects to the primary motor cortex, establishing a link between the cerebellum and motor areas of the cerebrum. It should be noted that ascending cerebellar projections, particularly from the dentate nucleus, also target nonmotor regions of the cerebrum, primarily in the frontal lobe. The descending fibers mainly target the basilar pontine nuclei, inferior olivary nucleus, and several reticular nuclei. Additionally, a minor cerebellospinal pathway originates mainly from the fastigial nucleus, and the fastigial nucleus also has significant projections to the vestibular nuclei.

Regarding motor coordination, the activity of Purkinje cells in the cerebellar cortex is influenced by mossy fiber input, which excites granule cells and subsequently triggers the discharge of single action potentials in Purkinje cells known as simple spikes.
Unipolar brush cells have only a single dendrite that ends as a tight bunch of branchlets that resemble a brush. These cells receive excitatory input from mossy fibers and inhibitory input from Golgi cells. It is thought that they synapse with granule and Golgi cells, which would make these cells an excitatory feedforward link in the mossy fiber–parallel fiber pathway.
Candelabrum cells are GABAergic cells located in the Purkinje layer. Their dendrites and axons terminate in the molecular layer, where the axonal arborization pattern resembles a candelabrum.
The cerebellar nuclei are the main targets of the cerebellar cortex. This projection is topographically organized in such a way that each longitudinal strip of cortex targets a specific region of the cerebellar nuclei. The gross pattern is that the vermis projects to the fastigial and vestibular nuclei, the paravermal region projects to the interpositus, and the lateral hemisphere projects to the dentate nucleus.
The cerebellar nuclear neurons in turn provide the output from the cerebellum to the rest of the brain (with the primary exception of Purkinje cells that project to the
CHAPTER 9 Organization of Motor Function vestibular nuclei). In discussing the output of the cerebellar nuclei, it is useful to group the nuclear cells according to whether they are GABAergic because the GABAergic cells project back to the inferior olivary nucleus and form a negative-feedback loop to one of the cerebellum’s principal afferent sources. Of importance is that GABAergic cells project to the specific part of the inferior olivary nucleus from which they receive input and from which their overlying longitudinal strip of cortex receives climbing fibers. Thus the cerebellar cortex, cerebellar nuclei, and inferior olivary nucleus are functionally organized as a series of closed loops. The non-GABAergic, excitatory nuclear cells project to a variety of targets from the spinal cord to the thalamus. In general, each nucleus gives rise to crossed ascending and descending projections that leave the cerebellum via the superior cerebellar peduncle. The fastigial nucleus also gives rise to significant uncrossed fibers, as well as a second crossed projection called the uncinate gyrus, or hook bundle, that leaves via the inferior cerebellar peduncle.
Although there are differences in the specific targets of each nucleus, in general, the ascending cerebellar projections target midbrain structures, such as the red nucleus and superior colliculus, and the ventral lateral nucleus of the thalamus, which connects to the primary motor cortex and thereby links the cerebellum to motor areas of the cerebrum. (The cerebral motor areas are likewise linked to the cerebellum by multiple pathways, including ones that relay in the basilar pons and inferior olivary nucleus.) It should also be mentioned that ascending cerebellar projections, particularly from the dentate nucleus, also target nonmotor regions of the cerebrum, particularly in the frontal lobe. The descending fibers target mainly the basilar pontine nuclei, inferior olivary nucleus, and several reticular nuclei. Lastly, a small cerebellospinal pathway arises principally from the fastigial nucleus. In addition, the fastigial nucleus has significant projections to the vestibular nuclei.
Activity of Purkinje Cells in the Cerebellar Cortex in the Context of Motor Coordination
Mossy fiber input to the cerebellar cortex, via their excitation of granule cells, causes a Purkinje cell to discharge single action potentials, referred to as simple spikes (