Cerebellum• The cerebellum (Latin for little brain) is a region of the brain that plays an important role in motor control.• It is also involved in some cognitive functions such as attention and language, and probably in some emotional functions such as regulating fear and pleasure responses.• does not initiate movement but it contributes to coordination, precision, and accurate timing.• receives input from sensory systems and from other parts of the brain and spinal cord, and integrates these inputs to fine tune motor activity.• receives input from sensory systems and from other parts of the brain and spinal cord, and integrates these inputs to fine tune motor activity.
Structure• At the level of large scale anatomy, the cerebellum consists of a tightly folded and crumpled layer of cortex, with white matter underneath, several deep nuclei embedded in the white matter, and a fluid-filled ventricle at the base.• At the microscopic level, each part of the cortex consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry• At an intermediate level, the cerebellum and its auxiliary structures can be decomposed into several hundred or thousand independently functioning modules called "microzones" or "microcompartments".
Function• The cerebellum is comprised of small lobes and receives information from the balance system of the inner ear, sensory nerves, and the auditory and visual systems. It is involved in the coordination of motor movements as well as basic facets of memory and learning.
Subdivisionsflocculonodular lobe• The smallest region is often called the vestibulocerebellum. It is the oldest part in evolutionary terms• participates mainly in balance and spatial orientation• its primary connections are with the vestibular nuclei, although it also receives visual and other sensory input.• Damage to it causes disturbances of balance and gait.
spinocerebellum• also known as paleocerebellum.• functions mainly to fine-tune body and limb movements.• It receives proprioception input from the dorsal columns of the spinal cord as well as from visual and auditory systems.• It sends fibres to deep cerebellar nuclei that, in turn, project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.
cerebrocerebellum• also known as neocerebellum.• It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei and sends output mainly to the ventrolateral thalamus and to the red nucleus.
Cell Components• Two types of neuron play dominant roles in the cerebellar circuit:• Purkinje cells• granule cells.• Three types of axons also play dominant roles:• mossy fibers• climbing fibers (which enter the cerebellum from outside)• parallel fibers (which are the axons of granule cells).• There are two main pathways through the cerebellar circuit, originating from mossy fibers and climbing fiber limbing fibers, both eventually terminating in the deep cerebellar nuclei.
Purkinje cells• Purkinje cells are among the most distinctive neurons in the brain, and also among the earliest types to be recognized.• Purkinje cells are a class of GABAergic neurons located in the cerebellar cortex.• named after their discoverer, Czech anatomist Jan Evangelista Purkyně• -with an intricately elaborate dendritic arbor, characterized by a large number of dendritic spines.
Granule Cells• Granule cells refer to tiny neurons that are around 10 micrometres in diameter.• found within the granular layer of the cerebellum• In humans, estimates of their total number average around 50 billion, which means that about 3/4 of the brains neurons are cerebellar granule cells.• A granule cell emits only four to five dendrites, each of which ends in an enlargement called a dendritic claw. These enlargements are sites of excitatory input from mossy fibers and inhibitory input from Golgi cells.
Mossy fibers• In the human cerebellum, the total number of mossy fibers has been estimated at about 200 million.• form excitatory synapses with the granule cells and the cells of the deep cerebellar nuclei.• generates a series of enlargements called rosettes
Climbing fibers• Climbing fibers are the name given to a series of neuronal projections from the inferior olivary nucleus located in the medulla oblongata.• Climbing fiber activation is thought to serve as a motor error signal sent to the cerebellum, and is an important signal for motor timing.• carry information from various sources such as the spinal cord, vestibular system, red nucleus, superior colliculus, reticular formation and sensory and motor cortices.
Deep nuclei• These nuclei receive inhibitory (GABAergic) inputs from Purkinje cells in the cerebellar cortex and excitatory (glutamatergic) inputs from mossy fiber and climbing fiber pathways• Most output fibers of the cerebellum originate from these nuclei