CEREBELLUM



WHAT IS CEREBELLUM ?

The cerebellum is a central organ for motor balance control. The main functions of the cerebellum are control of balance, posture, gait, coordination

and the regulation of muscle tone. Cerebellum lies in the fossa posterior and has got two hemispheres and the vermis. It’s connected to the brain by the three cerebellar peduncles. In superior or inferior views, the shape of the cerebellum is like a butterfly. Each hemisphere consists of 3 lobes separated by deep and distinct fissures.


ANATOMY OF CEREBELLUM

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

tentoriumcerebelli; all of its connectionswith other parts ofthe brain travelthroughthe pons. Anatomists classify the cerebellum as part of the metencephalon, which also includes the pons; the metencephalon is the upper part of the rhombencephalonor "hindbrain". Like the cerebral cortex,the cerebellumis dividedinto two cerebellarhemispheres;it also contains a narrow


midline zone(the vermis).Aset oflarge foldsis,by convention,used to dividethe overall

structure into 10 smaller "lobules".Becauseof itslarge number of tiny granulecells,the cerebellumcontains more neurons than the total from the rest of the

brain,but takes up only 10% of the total brainvolume.



The cerebellum has 3 functional parts:

Archicerebellum (vestibulocerebellum):

The central area is the vermis (“worm”). It includes the flocculonodular lobe, which is located in the medial zone. It helps maintain equilibrium and coordinate eye, head, and neck movements; it is closely connected with the vestibular nuclei.

Midline vermis (paleocerebellum):

It’s a lateral "wings" or lobes are the cerebellar hemispheres. It helps coordinate trunk and leg movements. Vermis lesions result in abnormalities of stance and gait.

Lateral hemispheres (neocerebellum):

They control quick and finely coordinated limb movements, predominantly of the arms.

Cerebellar cortex contains three layers:

The molecular layer contains stellate cells, basket cells, and the dendritic arbor of the Purkinje cells.

The Purkinje cell layer is found between the molecular and granule cell layers.

The granular layer is the inner layer overlying the white matter. It contains granule cells,

Golgi cells, and cerebellar glomeruli.


Neural pathways.

1. Afferent connections.

· The three large whitematter tracts (peduncles) of the cerebellum convey afferent input to the cerebellar cortex from the cerebral cortex, pontine nuclei, the brain stem nuclei of the trigeminal, vestibular, and cochlear nerves, and the spinal cord.

· This structure contains the major output from the cerebellum, the dentatothalamic tract, which

terminates in the ventral lateral nucleus of the thalamus. It contains one major afferent pathway, the

ventral superior cerebellar tract.

· The middle cerebellar peduncle carries fibers of pontine origin.

· The inferior cerebellar peduncle carries fibers from the vestibular nerve and nucleus to theflocculonodular lobe and fastigial nucleus, and from the contralateral inferior olive to the cerebellar hemispheres (olivocerebellar tract), as well as proprioceptive input from the posterior spinocerebellar tract and fibers from the brain stem reticular formation.


Neural Pathways

2. Efferent connections.

· The cerebellar nuclei (fastigial, globose,

emboliform, and dentate) project via the (contralateral) superior cerebellar peduncle to the red nucleus, thalamus, and reticular formation.

· The thalamus projects in turn to the premotor and primary motor cortex, whose output travels down to the pons, which projects back to the cerebellum, forming a neuroanatomical circuit.

· Cerebellar output influences (ipsilateral) spinal motor neurons by way of the red nucleus and rubrospinal tract.

· The inferior cerebellar peduncle projects to the vestibular nuclei and brain stem reticular formation (completing the vestibulocerebellar feedback loop) and influences spinal motor neurons by way of the vestibulospinal and reticulospinal tracts.


Neural Pathways.

3.Posterior and Anterior Spinocerebellar Tracts

Posterior spinocerebellar tract (Flechsig's).

•The fibers from the muscle spindles and tendon organs divide into numerous collaterals after entering the spinal cord.

•Some of these collateral fibers make synaptic contact directly onto the large α motor neurons of the anterior horn.

•Other collateral fibers arising at thoracic, lumbar, and sacral levels terminate in a column-shaped nucleus occupying the base of the posterior horn at levels C8-L2, which is named the intermediolateral cell column or thoracic nucleus, or Clarke’s column.

•The postsynaptic second neurons with cell bodies lying in this nucleus are the origin of the posterior

spinocerebellar tract, whose fibers are among the most rapidly conducting of any in the body.

•The posterior spinocerebellar tract ascends the spinal cord ipsilaterallyin the posterior portion of the

lateral funiculus and then travels by way of the inferior cerebellar peduncle to the cerebellarvermis.



Neural Pathways.

The anterior (Gowers') spinocerebellar tract (tractus spinocerebellaris anterior).

•The first neuron is common with the posterior tract. The cells of the second neurons are in the posterior

horn.

•Their axons form the anterior spinocerebellar tract and stretch in the anterior parts of the lateral white

column on their side and on the opposite side to which they cross through the white commissure.

•The tract ascends through the medulla oblongata and the pons - to the superior medullary velum where it

again crosses to the other side.

•Then the fibres enter the cerebellum through its superior peduncles and terminate in the cortex of the

vermis. Thus, this tract forms two decussations and proprioceptive sensibility is carried to the same side

from which it had gone.


SYNDROME OF CEREBELLUM

Incoordination of voluntary movements that occur as a manifestation of CEREBELLAR DISEASES.


Characteristic features include:

a tendency for limb movements to overshoot or undershoot a target (dysmetria),

a tremor that occurs during attempted movements (intention TREMOR),

impaired force and rhythm of rapidly alternating movements (adiadochokinesis), and gait ataxia.


Symptoms :

Limb motor deficits .

Increased falls .

Discoordination .

Muscle tremors .

Speech difficult.


Signs of Lesions.

Ataxia - it’s unstady, wide-based gait; decomposition of movement; it’s inability to correctly sequence fine, coordinated acts;

Static ataxia develops at vermix lesion and means standing and walking disorders.

Dinamic ataxia develops at lesion of hemispheres. The patient is asked to touch the tip of his nose with the tip of his index finger slowly with his eyes open (the finger nose test). Then this is repeated with the eyes closed.

To test the lower extremities the patient is asked to touch the knee by the opposite knee and slide it down the shin bone (the heel knee test) with the opened and closed eyes. Incoordination, not of sensory origin (cerebellar), is present with both the eyes open and closed. These tests recognize dinamic ataxia.



Signs of lesionSigns of lesion

The Romberg test recognizes static ataxia. Your patient stand with heels and toes together with open eyes and then with closed eyes. The tendency to unstable position with the eyes close provides a positive Romberg probe.


Signs of lesion

Hypermetría : Occurs when a person executes a movement and fails to interrupt it. Once the goal has been achieved, through the executed movement, these people exaggerate the movements and continue moving.

Asynergy : Lack of coordination between the related muscles in the realization of a certain movement. Babinski points out that it is not an incoordination, but a disturbance in the faculty of association of elementary movements in complex acts.

Discronometry : Affectation of the movements related to the moment of beginning and ending of the same, as well astheir total duration.

Adiadocokinesia , Inability to control certain muscle movements. This sign is notorious when it comes to stopping one impulse and replacing it with another.


Hypotonia

That is, under muscle tone. This symptom is characterized by decreased resistance to palpation or passive manipulation of muscles. Usually, hypotonia is accompanied by a decrease in Osteotendinous reflexes And pendular type. One way to determine these effects is with the Stewart Holmes test, in which

the patient is asked to flex his arm and resist. Meanwhile, the person performing the test will try to bring it to him. The effect is that, when released, the patient will hit hisface with his own arm. In the case of a person who lacks a disease that affects the

cerebellum, the triceps would stop and, in this way, the flexion of the arm would be stopped.


Intention tremor

Present Tremors which can be easily seen, in the performance of movements involving the fine musculature. That is to say, they are imprecise movements, for example: to fasten the buttons, to write.


Reflex disorders

They present reflexes for a longer time. In the case of osteotendinous reflex, there is a pendular movement of the knee after having Patellar tendon .


Nystagmus

Ocular movement disorder, similar to ataxia of these muscles. This symptom is a rhythmic oscillation of the eyes which is most easily demonstrated by diverting the eyes in a horizontal direction. It may occur that the oscillation has the same velocity in both directions (peduncular nystagmus) or that it is faster in one direction than in another (jerking nystagmus).


Dysarthria

The Dysarthria Is produced by ataxia in the muscles of the larynx. The articulation of words occurs in jolts and the syllables are normally emitted from each other.


Causes :

Bilateral frontoparietal polymicrogyria .

Hypoparathyroidism .

Joubert syndrome .

Arsenic trioxide .

Ataxia telangiectasia.



Test used for evaluation of cerebellum system

1. Heel shin test .

2. Rebound test or stewart .

3. Finger to finger or finger to nose test.

4. Babinski asynergia test.

5. Romberg test,

6. Tendon gait .

7. Flank gait.



Important Features of Cerebellar Pathways

Vestibulo-cerebellar tract

•Receives inputs from the vestibular system and visual areas;

•Output to vestibular nuclei;

•Controls equilibrium (balance) and eye movements;


Spino-cerebellar tract

•Is medially placed and it consists of the vermis and the intermediate zones;

•Input from spinal interneurons, sensorimotor cortex, auditory, visual and vestibular Systems.

•Output from the vermis to fastigial nucleus and then to vestibular nucleus and reticular formation in

brainstem;

•Output from intermediate zone to interposed nucleus and then to red nucleus of brainstem andventrolateral nucleus of thalamus;

•Fastigial nucleus is important in posture and locomotion;

•Interposed nucleus acts to control stretch reflexes and other somatosensory reflexes and damp tremor;


Cerebro-cerebellar pathway

• Input from cerebral cortex

•Output to dentate nucleus and then to ventrolateral thalamus to motor cortex and

premotor cortex

•Important for planning and initiation of volitional movement.



TREATMENT

In the case of this syndrome, the most widespread treatment and likely to yield better results is the treatmet of main (primarily) disease. In order to be successful, it is necessary to carry out an evaluation first and see which aspects to work on.


In this way, you can make a work plan adapted to the needs of the patient. Normally, the therapy is aimed at improving the coordination of movements, reinserting the functional automatisms, as well as re- educating the balance and gait.


The need for further medical treatment and / or prescribing will be determined by the health care provider and is probably determined by the

etiology of the cerebellar syndrome depending on the patient, as well as their needs and the manifestations of the disease.

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