cerebellum

enUK

cerebellum

(sĕr'əbĕl`əm), portion of the brainbrain,
the supervisory center of the nervous system in all vertebrates. It also serves as the site of emotions, memory, self-awareness, and thought. Anatomy and Function
..... Click the link for more information. that coordinates movements of voluntary (skeletal) muscles. It contains about half of the brain's neurons, but these particular nerve cells are so small that the cerebellum accounts for only 10% of the brain's total weight. The cerebellum operates automatically, without intruding into consciousness; motor impulses from the cerebrum are organized and modulated before being transmitted to muscle. As the muscle tissue responds, its sensory nerve cells return information to the cerebellum. Thus, throughout periods of muscular activity, the cerebellum adjusts speed, force, and other factors involved in movement. The overall effect is a smooth, balanced muscular activity. If the cerebellum is injured, an activity like walking becomes spasmodic: the muscles involved contract too much or too little and operate out of sequence. Maintaining muscle tone is also a function of the cerebellum. Filling most of the skull behind the brain stem and below the cerebrum, the human cerebellum approximates an orange in size and consists of two hemispherical lobes. The grooved surface of the cerebellum is gray matter, composed chiefly of nerve cells. The interior, dense with nerve fibers, makes up the white matter. Five different nerve cell types make up the cerebellum: stellate, basket, Purkinje, Golgi, and granule cells. The Purkinje cells are the only ones to send axons out of the cerebellum. Three main nerve tracts link the cerebellum with other brain areas. Injury to the cerebellum usually results in disruption of eye movements, balance, or muscle tone.

Cerebellum

in vertebrates and man, the division of the brain responsible for the coordination of movement and the maintenance of the body’s posture, tone, and balance and functionally involved in the regulation of autonomic, sensory, adaptive, tropic, and conditioned reflexive activities.

The cerebellum develops from a thickening of the dorsal wall of the neural tube. Evolutionarily, it first appears in cyclostomes, such as lampreys and hagfish, as “auricles” (the archicerebellum) that receive information primarily from the vestibular apparatus and lateral line organs. In addition to the archicerebellum, rays and sharks have a paleocerebellum that receives impulses chiefly from receptors of the muscles, tendons, joints, and sense organs. Mammals, unlike the lower classes of vertebrates, have a cerebellum with distinct hemispheric structures (the neocerebellum) that receives information primarily from the cerebral cortex and the visual and acoustic receptors. The degree of cerebellar development varies mainly with the level of development of motor activity. Therefore, in mobile animals such as birds, the cerebellum is comparatively large.

In man, the cerebellum is situated in the posterior cranial fossa under the occipital lobes of the cerebrum and above the medulla oblongata. It has two hemispheres connected by a median section called the vermis. The bodies of nerve cells form its gray surface layer (the cerebellar cortex). Paired nuclei of the gray matter are distributed in the cerebellum’s white matter, which consists of nerve fibers. Three pairs of cerebellar peduncles connect the cerebellum to the higher and lower divisions of the brain (the corpora quadrigemina, the pons, and the medulla oblongata).

The cortex of the cerebellum is more or less the same in all vertebrates. It consists of three layers made up of five types of cells, of which four are inhibitory. The surface (molecular) layer covers the Purkinje (gangliar) layer, which, in turn, covers the granular (deep) layer. Neural impulses reach the cortex mainly along the mossy fibers and, to some extent, along the climbing fibers. The axons of the Purkinje cells originating in the ganglionic layer are the only exit from the cortex, and they end at the cerebellar nuclei.

Data on cerebellar functions have been obtained primarily by complete or partial removal of the cerebellum, by cerebellar stimulation, and, in recent years, by electrophysiological methods. In man, congenital developmental anomalies or injuries disrupt equilibrium, decrease muscle tone, and impair the coordination of the force, degree, and rate of muscle contractions. They may cause tremors when voluntary movements are performed, or they may cause the patient to tire easily. These disturbances are less pronounced in mammals than in other animals. Mammals also compensate for the loss or impairment of these functions more quickly and more completely than other animals.

Removal of the cerebellum alters conditioned reflexive activity. Electric stimulation of certain regions of the cerebellum elicits motor reactions in different muscle groups of the eyes, head, and extremities and decreases the tone of the extensor muscles. It also produces shifts in physiological processes associated with the autonomic nervous system. These shifts are manifested by changes in the activities of the alimentary canal and the cardiovascular and respiratory systems, as well as by changes in thermoregulation and metabolism.

The bioelectric activity of the cerebellum is characterized by rapid and slow potentials. The slow rhythms are associated with the cerebral cortex; the rapid rhythms are an internal property of the cerebellum. Bioelectric potentials arise in certain regions of the cerebellar cortex in response to the stimulation of various regions of the cerebrum; the proprioreceptors of the muscles, the tendons and ligaments; and the receptors of the viscera, skin, eyes, and ears. All of these phenomena are indications of the complex and varied functions of the cerebellum, which may be regarded as a universal regulator of the body’s somatic and autonomic functions.

REFERENCES

Grigor’ian, R. A., and V. V. Fanardzhian. “Mozzhechok.” In Obshchaia i chastnaia fiziologiia nervnoi sistemy. Leningrad, 1969.
Fiziologiia cheloveka. Moscow, 1972.
Dow, R. S., and G. Moruzzi. The Physiology and Pathology of the Cerebellum. Minneapolis, Minn., 1958.
Eccles, J. C, M. Ito, and J. Szentagothai. The Cerebellum as a Neuronal Machine. Berlin, 1967.

I. V. ORLOV

cerebellum

[‚ser·ə′bel·əm] (cell and molecular biology) The part of the vertebrate brain lying below the cerebrum and above the pons, consisting of three lobes and concerned with muscular coordination and the maintenance of equilibrium.

cerebellum

one of the major divisions of the vertebrate brain, situated in man above the medulla oblongata and beneath the cerebrum, whose function is coordination of voluntary movements and maintenance of bodily equilibrium

cerebellum

enUK

cerebellum

[ser″ĕ-bel´um] the part of the metencephalon situated on the back of the brainstem, to which it is attached by three peduncles on each side (the peduncles" >cerebellar peduncles); it consists of a median lobe (vermis) and two lateral lobes (the hemispheres" >cerebellar hemispheres). See also brain.

cer·e·bel·lum

, pl.

ce·re·bel·la

(ser'e-bel'ŭm, -bel'ă), [TA] The large posterior brain mass lying posterior (dorsal) to the pons and medulla and inferior to the tentorium cerebelli and posterior portion of the cerebrum; it consists of two lateral hemispheres united by a narrow middle portion, the vermis. [L. dim. of cerebrum, brain]

cerebellum

(sĕr′ə-bĕl′əm)n. pl. cere·bellums or cere·bella (-bĕl′ə) The trilobed structure of the brain, lying posterior to the pons and medulla oblongata and inferior to the occipital lobes of the cerebral hemispheres, that is responsible for the regulation and coordination of complex voluntary muscular movement as well as the maintenance of posture and balance.

cer′e·bel′lar (-bĕl′ər) adj.

cer·e·bel·lum

, pl. cerebella, pl. cerebellums (serĕ-belŭm, -ă, -ŭmz) [TA] The large posterior brain mass lying dorsal to the pons and medulla and ventral to the posterior portion of the cerebrum; it consists of two lateral hemispheres united by a narrow middle portion, the vermis. [L. dim. of cerebrum, brain]

cerebellum

The smaller sub-brain lying below and behind the CEREBRUM. The cerebellum has long been thought to be concerned only with the coordination of information concerned with posture, balance and fine voluntary movement. Recent studies have shown, however, that the cerebellum functions to assist in many cognitive and perceptual processes. The cerebellum may also have a role to play in coordinating sensory input, and even in memory, attention and emotion.

cerebellum

the anterior dorsal (and largest) part of the HINDBRAIN which controls balance, muscle tone and the coordination of voluntary muscle. It is best developed in birds and mammals; in the latter there is a cortex of grey matter and the surface is complexly folded. The folds are lined with PURKINJE CELLS. Removal of the cerebellum unbalances an animal and affects the accuracy of voluntary movements such as walking, swimming, knitting.

Cerebellum

The part of the brain involved in coordination of movement, walking, and balance.Mentioned in: Alcohol-Related Neurologic Disease, Ataxia-Telangiectasia, Progressive Supranuclear Palsy

cer·e·bel·lum

Patient discussion about cerebellum

Q. can you recover after a cerebellar stroke? A. You can recover after a cerebellar stroke but the process takes time and rehabilitation. With the right kind of rehab people reach great results, supposing of course the initial injury allows it.

Q. Is there any problem, if an arachnoid cyst ,2cmx1.5cm size, rostral to cerebellar region left untreated? symptoms: repeated headaches, twitching of muscles, tirednessA. An arachnoid cyst that leads to symptoms usually needs treatment. Mild symptoms as you suggested are ok to left untreated however gradual onset of new symptoms may arise such as seizures, paralysis and other complications, therefore once symptoms occur one should consider treatment.

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noun a major division of the vertebrate brain

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