Editing Cerebellum (section)

===Gross anatomy===
[[File:Sobo 1909 653.png|thumb|right|View of the cerebellum from above and behind]]
The cerebellum is located in the [[posterior cranial fossa]]. The [[fourth ventricle]], [[pons]] and [[medulla oblongata|medulla]] are in front of the cerebellum.<ref name=Gray>{{cite book | veditors = Standring S, Borley NR |chapter=Chapter 20 |page=297 |title=Gray's anatomy : the anatomical basis of clinical practice |date=2008|publisher=Churchill Livingstone |location=London |isbn=978-0-8089-2371-8 |edition=40th |ref={{harvid|Gray's Anatomy|2008}}|display-editors=etal}}</ref> It is separated from the overlying [[cerebrum]] by a layer of leathery [[dura mater]], the [[cerebellar tentorium]]; 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 [[cerebellar hemisphere]]s; it also contains a narrow midline zone (the [[cerebellar vermis|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 cell]]s, the cerebellum contains more [[neuron]]s than the total from the rest of the brain, but takes up only 10% of the total brain volume.<ref name=SOB/> 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.<ref>{{cite journal | vauthors = Herculano-Houzel S | title = Coordinated scaling of cortical and cerebellar numbers of neurons | journal = Frontiers in Neuroanatomy | volume = 4 | pages = 12 | year = 2010 | pmid = 20300467 | pmc = 2839851 | doi = 10.3389/fnana.2010.00012 | doi-access = free }}</ref>

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 [[grey matter|gray matter]]: the '''cerebellar cortex'''. Each ridge or gyrus in this layer is called a '''folium'''. High‑resolution MRI finds the adult human cerebellar cortex has an area of 730&nbsp;square cm,<ref name="Lyu Wu Huynh Ahmad 2024 p.">{{cite journal |last1=Lyu |first1=Wenjiao |last2=Wu |first2=Ye |last3=Huynh |first3=Khoi Minh |last4=Ahmad |first4=Sahar |last5=Yap |first5=Pew-Thian |date=2024 |title=A multimodal submillimeter MRI atlas of the human cerebellum |journal=Scientific Reports |volume=14 |issue=1 |page= 5622|doi=10.1038/s41598-024-55412-y |issn=2045-2322 |pmc=10920891 |pmid=38453991|bibcode=2024NatSR..14.5622L }}</ref> packed within a volume of dimensions 6&nbsp;cm × 5&nbsp;cm × 10&nbsp;cm.<ref name=SOB/> Underneath the gray matter of the cortex lies [[white matter]], made up largely of [[myelin]]ated nerve fibers running to and from the cortex. Embedded within the white matter—which is sometimes called the ''[[arbor vitae (anatomy)|arbor vitae]]'' (tree of life) because of its branched, tree-like appearance in cross-section—are four [[deep cerebellar nuclei]], composed of gray matter.<ref name=Ghez/>

Connecting the cerebellum to different parts of the nervous system are three paired [[cerebellar peduncle]]s. These are the [[superior cerebellar peduncle]], the [[middle cerebellar peduncle]] and the [[inferior cerebellar peduncle]], named by their position relative to the vermis. The superior cerebellar peduncle is mainly an output to the cerebral cortex, carrying efferent fibers via [[thalamic nuclei]] to [[upper motor neuron]]s in the cerebral cortex. The fibers arise from the deep cerebellar nuclei. The middle cerebellar peduncle is connected to the pons and receives all of its input from the pons mainly from the [[pontine nuclei]]. The input to the pons is from the cerebral cortex and is relayed from the pontine nuclei via transverse pontine fibers to the cerebellum. The middle peduncle is the largest of the three and its afferent fibers are grouped into three separate fascicles taking their inputs to different parts of the cerebellum. The inferior cerebellar peduncle receives input from afferent fibers from the vestibular nuclei, spinal cord and the tegmentum. Output from the inferior peduncle is via efferent fibers to the vestibular nuclei and the [[reticular formation]]. The whole of the cerebellum receives modulatory input from the inferior olivary nucleus via the inferior cerebellar peduncle.<ref name=Purves/>

====Subdivisions====
[[File:CerebellumDiv.png|thumb|right|Schematic representation of the major anatomical subdivisions of the cerebellum. Superior view of an "unrolled" cerebellum, placing the vermis in one plane.]]
Based on the surface appearance, three [[Lobe (anatomy)|lobes]] can be distinguished within the cerebellum: the [[Anterior lobe of cerebellum|anterior lobe]] (above the [[Primary fissure of cerebellum|primary fissure]]), the [[Posterior lobe of cerebellum|posterior lobe]] (below the primary fissure), and the [[flocculonodular lobe]] (below the posterior fissure). These lobes divide the cerebellum from rostral to caudal (in humans, top to bottom). In terms of function, however, there is a more important distinction along the medial-to-lateral dimension. Leaving out the flocculonodular lobe, which has distinct connections and functions, the cerebellum can be parsed functionally into a medial sector called the [[spinocerebellum]] and a larger lateral sector called the [[cerebrocerebellum]].<ref name=Ghez/> A narrow strip of protruding tissue along the midline is called the [[cerebellar vermis]]. (''Vermis'' is Latin for "worm".)<ref name=Ghez/>

The smallest region, the flocculonodular lobe, is often called the [[vestibulocerebellum]]. It is the oldest part in evolutionary terms (archicerebellum) and participates mainly in [[sense of balance|balance]] and spatial orientation; its primary connections are with the [[vestibular nuclei]], although it also receives visual and other sensory input. Damage to this region causes [[balance disorder|disturbances of balance]] and [[gait (human)|gait]].<ref name=Ghez/>

The medial zone of the anterior and posterior lobes constitutes the spinocerebellum, also known as paleocerebellum. This sector of the cerebellum functions mainly to fine-tune body and limb movements. It receives [[proprioception|proprioceptive]] input from the dorsal columns of the [[spinal cord]] (including the [[spinocerebellar tract]]) and from the [[Cranial nerves|cranial]] [[trigeminal nerve]], as well as from visual and [[auditory system|auditory]] systems.<ref>{{cite journal | vauthors = Snider RS, Stowell A |title=Receiving Areas of the Tactile, Auditory, and Visual Systems in the Cerebellum |journal=Journal of Neurophysiology |date=1 November 1944 |volume=7 |issue=6 |pages=331–357 |doi=10.1152/jn.1944.7.6.331 |s2cid=146700933 |doi-access=free }}</ref> It sends fibers to deep cerebellar nuclei that, in turn, project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.<ref name=Ghez/>

The lateral zone, which in humans is by far the largest part, constitutes the cerebrocerebellum, also known as neocerebellum. It receives input exclusively from the cerebral cortex (especially the [[parietal lobe]]) via the [[pontine nuclei]] (forming cortico-ponto-cerebellar pathways), and sends output mainly to the ventrolateral [[thalamus]] (in turn connected to motor areas of the [[premotor cortex]] and [[primary motor area]] of the cerebral cortex) and to the [[red nucleus]].<ref name=Ghez/> There is disagreement about the best way to describe the functions of the lateral cerebellum: It is thought to be involved in planning movement that is about to occur,<ref>{{cite book | vauthors = Kingsley RE |title=Concise Text of Neuroscience |edition=2nd |publisher=Lippincott Williams & Wilkins |year=2000 |isbn=978-0-683-30460-2}}</ref> in evaluating sensory information for action,<ref name=Ghez/> and in a number of purely cognitive functions, such as determining the verb which best fits with a certain noun (as in "sit" for "chair").<ref>{{cite journal | vauthors = Petersen SE, Fox PT, Posner MI, Mintun M, Raichle ME | title = Positron emission tomographic studies of the processing of single words | journal = Journal of Cognitive Neuroscience | volume = 1 | issue = 2 | pages = 153–70 | year = 1989 | pmid = 23968463 | doi = 10.1162/jocn.1989.1.2.153 | s2cid = 35159122 }}</ref><ref>{{cite journal | vauthors = Timmann D, Daum I | title = Cerebellar contributions to cognitive functions: a progress report after two decades of research | journal = Cerebellum | volume = 6 | issue = 3 | pages = 159–62 | year = 2007 | pmid = 17786810 | doi = 10.1080/14734220701496448 | s2cid = 25671398 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Strick PL, Dum RP, Fiez JA | s2cid = 1066141 | title = Cerebellum and nonmotor function | journal = Annual Review of Neuroscience | volume = 32 | pages = 413–34 | year = 2009 | pmid = 19555291 | doi = 10.1146/annurev.neuro.31.060407.125606 }}</ref><ref>{{cite journal | vauthors = Buckner RL | title = The cerebellum and cognitive function: 25 years of insight from anatomy and neuroimaging | journal = Neuron | volume = 80 | issue = 3 | pages = 807–15 | date = October 2013 | pmid = 24183029 | doi = 10.1016/j.neuron.2013.10.044 | doi-access = free }}</ref>