The cerebellum issituated in theposterior cranialfossa. It is the largestpart of the hindbrainand lies posterior tothe fourth ventricle,the pons, and themedulla oblongata.
CEREBELLUM The cerebellum is located behind the dorsal aspect of the pons and the medulla. A midline portion, the vermis, separates two lateral lobes, or cerebellar hemispheres. The cerebellum consists of the cerebellar cortex and the underlying cerebellar white matter Four paired deep cerebellar nuclei are located within the white matter of the cerebellum
The cerebellum isdivided into three mainlobes:the anterior lobethe middle(posterior)lobe the flocculonodularlobe.A deep horizontal fissure that is foundalong the margin of the cerebellumseparates the superior from theinferior surfaces; it is of nomorphologic or functional significance
Structure of the CerebellumThe cerebellum is composed ofan outer covering of gray mattercalled the cortex and inner whitematter.
A section made through the cerebellum parallelwith the median plane divides the folia at rightangles, and the cut surface has a branchedappearance, called the arbor vitae.
The gray matter of thecortex throughout itsextent may be divided intothree layers:(1) an external layer, the molecular layer(2) a middle layer, the Purkinje cell layer(3) an internal layer, the granular layer .
Functional Areas of the Cerebellar CortexClinically it is possible to divide up the cerebellar cortexinto three functional areas.1.The cortex of the vermis influences the movements ofthe long axis of the body, namely, the neck, theshoulders, the thorax, the abdomen, and the hips. 2.Immediately lateral to the vermis is a so-calledintermediate zone of the cerebellar hemisphere. Thisarea has been shown to control the muscles of thedistal parts of the limbs, especially the hands and feet. 3.The lateral zone of each cerebellar hemisphereappears to be concerned with the planning of sequentialmovements of the entire body and is involved with theconscious assessment of movement errors.
Intracerebellar NucleiFour masses of gray matter are embedded in the whitematter of the cerebellum on each side of the midline.From lateral to medial, these nuclei are the dentate, theemboliform, the globose, and the fastigial.
White MatterThere is a small amount of white matter inthe vermis; it closely resembles the trunkand branches of a tree and thus is termedthe arbor vitae . There is a large amount ofwhite matter in each cerebellarhemisphere.The white matter is made up of threegroups of fibers: (1) intrinsic,(2) afferent, (3) efferent.
Cerebellar PedunclesThe cerebellum is linked toother parts of the central nervoussystem by numerous efferent andafferent fibers that are groupedtogether on each side into threelarge bundles, or peduncles. The superior cerebellarpeduncles connect the cerebellumto the midbrain, the middle cerebellarpeduncles connect the cerebellumto the pons, andthe inferior cerebellar pedunclesconnect the cerebellum to themedulla oblongata.
CEREBELLAR FUNCTIONS The cerebellum has several main functions: coordinating skilled voluntary movements by influencing muscle activity, controlling equilibrium and muscle tone through connections with the vestibular system and the spinal cord. There is a somatotopic organization of body parts within the cerebellar cortex. In addition, the cerebellum receives collateral input from the sensory and special sensory systems.
Each cerebellar hemisphere is connected bynervous pathways principally with the sameside of the body; thus, a lesion in onecerebellar hemisphere gives rise to signsand symptoms that are limited to the sameside of the body.
Diagnosis of Cerebellar disordersThe main clinical features of cerebellar disorders includeincoordination, imbalance, and troubles with stabilizing eyemovements. There are two distinguishable cerebellar syndromes –1. midline and 2.hemispheric.1.Midline cerebellar syndromes are characterized byimbalance.Persons are unsteady, they are unable to stand in with eyesopen or closed, and are unable to well perform tandem gait.trunkal ataxia ."titubation" or a bobbing motion of the head or trunk.also often affect eye movements. There may be nystagmus, ocular dysmetria.
Hemispheric cerebellar syndromes are characterized byincoordination of the limbs.There may be decomposition of movement, dysmetria, andrebound. Dysdiadochokinesis is the irregular performance of rapidalternating movements.Intention tremors may be present on an attempt to touch anobject.A kinetic tremor may be present in motion.The finger-to-nose and heel-to-knee tests are classic tests ofhemispheric cerebellar dysfunction.