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2.3. Balance between excitation and inhibition at the deep cerebellar nuclei.

Both the climbing and the mossy fibers stimulate the deep nuclear cells. And the Purkinje cells inhibit
them. Normally, the balance between these two effects is slightly in favour of excitation, so that, under
quiet conditions, the output from the deep nuclear cell remains relatively constant t a moderate level
of continuous stimulation. .

When a rapid motor movement is performed, the initiating signal from the cerebral motor cortex or
brain stem increases deep nuclear cell excitation, but a few milliseconds later, inhibitory signals from
the Purkinje cell circuit arrive. So, there is first a rapid excitatory signal sent by the deep nuclear cells
into the motor output pathway to enhance the motor movement, but this is followed by an inhibitory
signal.

This inhibitory signal is effective in providing damping to avoid overshooting of the muscle and
oscillation of the movement.

2.4. Other inhibitory cells in the cerebellum.

In addition to the deep nuclear cells (the granule cells and the Purkinje cells), there are two other types
of neurons located in the cerebellum: the basket cells and the stellate cells.

 These are inhibitory cells with short axons.
 Both types are located in the molecular layer of the cerebellar cortex, lying among and
stimulated by the small parallel fibers.
 These cells (the granule cells) send their axons at right angles across the parallel fibers and
cause lateral inhibition of adjacent Purkinje cells, thus sharpening the signal.

1) Stellate cells: these are located in the superficial part, oriented transversely. They synapse with
the Purkinje cell dendrites.
2) Basket cells: these have a stronger inhibitory response. These are located in the deep part,
oriented transversely. Its axons form a basket around the Purkinje cell axon hillock.

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