Neuronal Activity in Cerebellar Cortex and Nuclei

Neuronal Activity in Cerebellar Cortex and Nuclei

Functions of cerebellum are executed mainly by the impulses discharged from cerebellar nuclei. However, cerebellar cortex controls the discharge from nuclei constantly via the fibers of Purkinje cells. It is done in accordance with the signals received by cerebellar cortex from different parts of the brain and body via climbing and mossy fibers. Entire process involves a series of neuronal

activity:

1. Climbing fibers excite the Purkinje cells directly and cerebellar nuclei via collaterals, by releasing aspartate. Excitatory effect of climbing fiber on Purkinje cell is very strong because each climbing fiber ends on a single Purkinje cell.

2. Mossy fibers excite the Purkinje cells indirectly. In the glomeruli, mossy fibers release glutamate and excite the granule cells and Golgi cells. Collaterals of mossy fibers activate the cerebellar nuclei also by glutamate.

3. Granule cells, which are activated by mossy fibers in turn, excite the Purkinje cells, stellate cells and the basket cells through the parallel fibers. Neurotransmitter utilized by granule cells is glutamate or aspartate. Granule cells are the only excitatory cells in cerebellar cortex, while all other cells are inhibitory in function. Each mossy fiber innervates many Purkinje cells indirectly via granule cells. So, the excitatory effect of mossy fibers on Purkinje cells is weak.

4. Stellate cells and basket cells, which are activated by granule cells, inhibit the Purkinje cells by releasing GABA. This type of inhibition is called feed forward inhibition.

5. Golgi cell that is activated by mossy fibers, in turn, provides feedback inhibition to granule cells by releasing GABA, i.e. it inhibits the transmission of impulse from mossy fiber to granule cell

6. Cerebellar nuclei are excited by collaterals from climbing and mossy fibers. In turn, the nuclei send excitatory impulses to thalamus and different nuclei in brainstem.

7. However, signals discharged from Purkinje cells inhibit cerebellar nuclei via GABA. Purkinje cells.

Thus, it is clear that the cerebellar cortex plays an important role in modulating the excitatory signals

of following pathways:

i. From cerebellar nuclei to cerebral cortex via thalamus

ii. From final common motor pathway via brainstem and spinal cord.

Because of this activity of cerebellar cortex, movements of body are well organized and

coordinated.

CEREBELLAR NUCLEI

Cerebellar nuclei are the masses of gray matter scattered in the white matter of cerebellum. There are

four nuclei on either side.

1. Fastigial Nucleus

Fastigial nucleus is also known as nucleus fastigi. Phylogenetically, it is the oldest cerebellar nucleus. It

is placed near the midline on the roof of IV ventricle.

2. Globosus Nucleus

Globosus nucleus is situated lateral to nucleus fastigi. This is also known as nucleus globosus.

3. Emboliform Nucleus

Emboliform nucleus is also called nucleus emboliformis. This nucleus is below the nucleus fastigi and

nucleus globosus.

4. Dentate Nucleus

Dentate nucleus is also called nucleus dentatus. It is the largest cerebellar nucleus. As it is crenated, it is

called dentate nucleus. It is situated lateral to all the other nuclei.