CEREBELLUM

Kaan Yücel M.D., Ph.D. 28. April.2014 Monday

largest part of the hindbrain lies posterior to the fourth ventricle, pons, and medulla oblongata. situated in the posterior cranial fossa covered superiorly by tentorium cerebelli. made up of two lateral cerebellar hemispheres and a median vermis (L. “worm”). surface displays slender and parallel elevations (ridges) folia and depressions (grooves) known as sulci increase in the surface area of the cerebellar cortex.

CEREBELLUML. “little brain”

CEREBELLUM

CEREBELLUM

Though apparently smaller than the cerebral cortex, the cerebellum contains ~2X as many neurons as the cerebral cortex.

Its function is to make our movements as fast, accurate, smooth, and consistent as possible. Cerebellar damage does not cause paralysis but renders movements slow, inaccurate, inconsistent, and jerky.

Though the cerebellum sends very few fibers to the spinal cord it exerts a powerful influence on movements via projections, either direct or via one relay neuron, to the structures from which all four major descending motor tracks originate.

CEREBELLUM

Cerebellar PedunclesThe cerebellum is linked to other parts of the central nervous system by numerous efferent and afferent fibers that are grouped together on each side into three large bundles, or peduncles.

Superior cerebellar peduncles connect the cerebellum to the midbrainMiddle cerebellar peduncles connect the cerebellum to the ponsInferior cerebellar peduncles connect the cerebellum to the medulla oblongata.

On its ventral surface, near the middle cerebellar peduncle, a small, bulb-like region of each cerebellar hemisphere, known as the flocculus, is connected to a region of the vermis known as the nodulus.

CEREBELLUM

The effect of this fissuring is to give the cerebellum in section the appearance of a many branched tree which is called as arbor vitae; the tree of life.

The cerebellum has traditionally been recognized as having three anterior-posterior divisions: anterior lobe (lobules I – V) is separated from the posterior lobe by the primary fissure, and the posterior lobe (lobules VI – IX) is separated from the flocculonodular lobe (lobule X) by the posterolateral fissure (posterior fissure or uvulonodular fissure).

A deep horizontal fissure that is found along the margin of the cerebellum separates the superior from the inferior surfaces.

The anterior lobe receives its input primarily from the spinal cord and is referred to as the paleocerebellum.

The posterior lobe receives its input primarily from the cerebral cortex via relay neurons in the pontine nuclei and is called the neocerebellum.

The flocculonodular lobe receives most of its input from the vestibular system and is called the vestibulocerebellum.

CEREBELLUM

Plays a very important role in the control of posture and voluntary movements.

Unconsciously influences the smooth contraction of voluntary muscles and carefully coordinates their actions.

Each cerebellar hemisphere controls muscular movements on the same side of the body and that the cerebellum has no direct pathway to the lower motor neurons but exerts its control via the cerebral cortex and the brainstem.

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Composed of an outer covering of gray matter called the cortex and inner white matter.

Embedded in the white matter of each hemisphere are three masses of gray matter forming the intracerebellar nuclei (deep cerebellar nuclei).

CEREBELLUM

The human cerebellum contains more than 100 billion neurons, a number that represents about 80% of the total number of neurons in the brain.

The cortex of the cerebellum is deeply folded. If one looks at the human cerebral cortex,one can see about one third of it; two thirds is buried on the banks and depths of the fissures.

For the cerebellar cortex, one would see only about one tenth; 90% is buried within the fissures.

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The output from the cortex is mainly to the intracerebellar nuclei, which are buried within the white matter of the cerebellum.

The white matter consists of fibers coming into the cerebellum and the axons of the output neurons of the cerebellar cortex, Purkinje cells, coursing to terminate in the cerebellar nuclei.

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There are four nuclei on each side.

Most laterally is the dentate or lateral nucleus. Most medially is the fastigial or medial nucleus. Between the lateral and medial nuclei are the intermediate, or interpositus nuclei, the globose (more lateral) and emboliform (more medial).

CEREBELLUM

There are four nuclei on each side.

Most laterally is the dentate or lateral nucleus. Most medially is the fastigial or medial nucleus. Between the lateral and medial nuclei are the intermediate, or interpositus nuclei, the globose (more lateral) and emboliform (more medial).

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Functions of the cerebellumCerebellum makes an important contribution to the control of voluntary movement and movement coordination, as well as control of balance, gait, and posture. Functions- 3 major functional roles1. Coordination of Movement-the cerebellum controls the timing and pattern of muscle activation during movement.2. Maintenance of Equilibrium (in conjunction with the vestibular system)3. Regulation of Muscle Tone-modulates spinal cord and brain stem mechanisms involved in postural control.There is also strong evidence for a cerebellar role in cognition (memory, attention, language and executive functions), emotions, and anxiety. More @ Limbic System class!!!