Download 9-5_Neuronal connections of the cerebellar cortex excitatory

On the first picture, we can see where is the cerebral cortex, which is the grey matter. There are
three layers, the granule cell layer that is deepest, the Purkinje cell layer that is in the middle and the
molecular layer that is the most outer one.
The motor information input travels from the spinal cord, cerebral cortex and vestibular system via
mossy fibers.
And all outgoing neural impulses from the cerebellum travel via the deep cerebellar and vestibular
nuclei. Proper functioning of the neuronal pathway between mossy fibers, granular cells, parallel fibers, climbing fibers and Purkinje cells are thought to be essential for coordinated muscular movement.
The excitatory elements are the follows granule cells, mossy fibers and climbing fibers.
Granule cells are the smallest neurons in the brain. They have some small dendrites between 3 and 5,
and there are a lot of enlargement at end of the process. The granule cell axon runs toward the cortical surface, into the molecular layer where it divides in a "T". And then the axons form fascicle that
runs along perpendicular to the dendrite tree of the Purkinje cells.
Purkinje cells have thin and thick dendrites. Parallel fiber makes contact with thin dendrites, that has
a lot of spine. The little spine on it and each of these input makes a little input, but they can summate
to activate the Purkinje cell. Parallel fiber axons are also the main excitatory input to the Golgi, stellate and basket cells.
Mossy fibers contain all of the cerebellar inputs except one that belong to the climbing fiber. These
inputs derive from the spinal cord, cerebral cortex and the vestibular cortex. They are located centrally and branched apart from regular branches.
About the mossy-granule synapse (glomerulus): The cerebellar glomerulus is a small, intertwined
mass of nerve fiber terminals. It consists of post-synaptic granule cell dendrites and pre-synaptic Golgi cell axon terminals surrounding the pre-synaptic terminals of mossy fibers.
Climbing fibers arise only from the inferior olivary nucleus. They have myelinated axons, but they lost
myelin in the Purkinje layer. The non-myelinated axons are twisted around the dendrite tree of the
Purkinje cells. As I mentioned those Purkinje cells have thin and thick dendrites. Three different axons are ended on the thicker ones and one of them belongs to the climbing fibers. The Purkinje cells
have hundreds of connections with climbing fibers and one climbing fiber’s terminal make connection with 5 or 6 spines on the dendrite and that’s why the climbing fibers mean so great stimulation
input for the Purkinje cells but one fiber goes to only one Purkinje cell.
A current concept of the function of olivary from that the climbing fibers derive is a kind of error detection. When a particular action goes off target, inferior olivary nucleus neurons are activated. This
results in powerful activation of the target Purkinje cells through the climbing fibers. This powerful
activation of Purkinje cells inhibits the deep cerebellar nucleus neurons, hopefully terminating the
unwanted component of the action.
Parallel and mossy fiber release glutamate neurotransmitter while the climbing fibers release asparate.