<P> In addition to its direct role in motor control, the cerebellum is necessary for several types of motor learning, most notably learning to adjust to changes in sensorimotor relationships . Several theoretical models have been developed to explain sensorimotor calibration in terms of synaptic plasticity within the cerebellum . These models derive from those formulated by David Marr and James Albus, based on the observation that each cerebellar Purkinje cell receives two dramatically different types of input: one comprises thousands of weak inputs from the parallel fibers of the granule cells; the other is an extremely strong input from a single climbing fiber . The basic concept of the Marr--Albus theory is that the climbing fiber serves as a "teaching signal", which induces a long - lasting change in the strength of parallel fiber inputs . Observations of long - term depression in parallel fiber inputs have provided support for theories of this type, but their validity remains controversial . </P> <P> At the level of gross anatomy, the cerebellum consists of a tightly folded layer of cortex, with white matter underneath and a fluid - filled ventricle at the base . Four deep cerebellar nuclei are embedded in the white matter . Each part of the cortex consists of the same small set of neuronal elements, laid out in a highly stereotyped geometry . At an intermediate level, the cerebellum and its auxiliary structures can be separated into several hundred or thousand independently functioning modules called "microzones" or "microcompartments". </P> <P> The cerebellum is located in the posterior cranial fossa . The fourth ventricle, pons and medulla are in front of the cerebellum . It is separated from the overlying cerebrum by a layer of leathery dura mater, the tentorium cerebelli; all of its connections with other parts of the brain travel through the pons . Anatomists classify the cerebellum as part of the metencephalon, which also includes the pons; the metencephalon is the upper part of the rhombencephalon or "hindbrain". Like the cerebral cortex, the cerebellum is divided into two hemispheres; it also contains a narrow midline zone (the vermis). A set of large folds is, by convention, used to divide the overall structure into 10 smaller "lobules". Because of its large number of tiny granule cells, the cerebellum contains more neurons than the total from the rest of the brain, but takes up only 10% of the total brain volume . The number of neurons in the cerebellum is related to the number of neurons in the neocortex . There are about 3.6 times as many neurons in the cerebellum as in the neocortex, a ratio that is conserved across many different mammalian species . </P> <P> The unusual surface appearance of the cerebellum conceals the fact that most of its volume is made up of a very tightly folded layer of gray matter: the cerebellar cortex . Each ridge or gyrus in this layer is called a folium . It is estimated that, if the human cerebellar cortex were completely unfolded, it would give rise to a layer of neural tissue about 1 meter long and averaging 5 centimeters wide--a total surface area of about 500 square cm, packed within a volume of dimensions 6 cm × 5 cm × 10 cm . Underneath the gray matter of the cortex lies white matter, made up largely of myelinated nerve fibers running to and from the cortex . Embedded within the white matter--which is sometimes called the arbor vitae (tree of life) because of its branched, tree - like appearance in cross-section--are four deep cerebellar nuclei, composed of gray matter . </P>

Where is the cerebellum located in the brain