ANATOMIE
Pathologies that affect to us are mainly associated to the cerebellum and the cerebro spinal fluid. It is important to make a brief summary of its localization and physiologic functions in the organism.
THE CEREBELLUM
The cerebellum is called encephalom`s quiet area, mainly because the electrical excitation of this structure does not cause any sensation and rarely any motor movements. The cerebellum is vital for the dynamic muscular activity control like running, typewriting, playing the piano an speaking.
Cerebellum functions
How the cerebellum can have as much importance if it does not have direct control on the muscular contractions?
The cerebellum watches and establishes correctors adjustments to all the motor activities triggered by other parts of the encephalon. It receives present information of the peripheral parts of the body, to determine the instantaneous state of each one of these areas (its position, movement rates, the forces that act on him, etc.)
If the cerebellum and encephalon are not compared favorably, suitable corrector signals are transmitted immediately towards the motor system, to increase or to diminish the activity of specific muscles.
Therefore each point of the cerebellum represents a specific muscle or a certain joint; simultaneously it receives direct information from the motor outward to activate the muscle or the joint.
The cerebellum only acts in association with other motor parts of the Central Nervous System (SNC). This activity may come from the spinal cord, reticular formation, basal ganglions or motor areas in the cerebral outward.
It is seen that this feedback circuit is complicated and begins and finishes in the motor outward. In other words the cerebellum compares the outward intentions with corporal parts performances, in case that these do not agree each other. It calculates the "error" between both of them to be able to carry out the appropriate correction immediately.
The cerebellum appreciates the speed of movement automatically and calculates the time that is needed to reach the wished point.
Example. If the outward transmits a signal to move the hand towards a particular point, but the hand begins to move too much quickly, the hand will move beyond the wished point, the cerebellum can trigger restrained impulses that impede the movement of the hand and they will stop it in the precise point.
In the patients with important cerebellum damage the activation of the antagonistic muscles does not appear at the desirable moment, but that always happens too much late.
Damping function
The cerebellum cushions the muscular movements. ALL THE MOVEMENTS OF THE BODY ARE PENDULAR. All the pendular movements due to inertia have tendency to go of the initial project.
If a person has a cerebellum sickness, the conscious centers of the brain finishes realizing it and initiates a movement in opposite direction; but again the arm, due to inertia, go beyond the correct position and it will have to return to emit signals that tend to correct the error. Therefore the arm oscillates around the right point during several cycles before reaching it. This process is called action tremor.
The cerebellum damping mechanism, sometimes maintains the damping system as a traction reflect and sometimes it inhibits it, which demonstrates that the cerebellum system has a great amplitude of control that allows him to adapt to motor activities more complex than the traction reflection.
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The cerebellum predicting function
Another function of the cerebellum system is to help the SNC to predict the future positions of all the movable parts of the body.
It deduces the afferent signals, the rapidity with which the member moves and can predict the probable evolution of the movement of the time. This allows to the cerebellum, acting through the cerebral outward, to inhibit antagonistic muscles and to activate them when the movement approaches the wished point.
One of the characteristics of the normal motor function is the capacity to go from a movement to another one in an ordered succession. When the function of the cerebellum is altered and the subconscious capacity to recognize in advance how quickly the different parts from the body are going to move, is lost, also it becomes impossible to control the beginning of the following movement. The result is that the successive movements can begin too much soon or too much late. Therefore the movements become totally uncoordinated, such as those you need to write, to run, and to speak, not being able to follow one another in order.
Cerebellum predicting motor extra functions
The cerebellum can predict the intensity of progression of auditory or visual phenomena. It is very possible that the cerebellum supplies a basal time. It has been stated that the cerebellum has particularly importance to interpret space and temporal relations in the sensorial information.
Cerebellum function in the involuntary movements
The same type of error control is obtained for the involuntary and voluntary movements
Cerebellum function in the spinal reflected movements control
Trough a cerebellum-reticular feedback system increases considerably the spinal reflection power
Balance function
The semicircular conduits allow the SNC to anticipate that the rotator movements of the body might destroy the balance, and this prediction function causes contractions of corresponding muscles to even correct the disturbance before it happens.
Clinical anomalies of the cerebellum
The destruction of small portions of the cerebellum outward does not cause demonstrable anomalies of the motor function. In fact some months after destroying until half of the cerebellum outward, the motor functions will return to be almost normal but only if the person carry out all the movements slowly. In order to cause serious upheavals of the cerebellum, the injury must alter the deep cerebellum nucleus.
1. Disymmetry and Ataxia
They are both the most important symptoms of the cerebellum anomalies
In the disymmetry the movements are not corrected and usually they go of the wished point
Ataxia is uncoordinated movements.
2.Hypermetry=Past Pointing
It is an asymmetry manifestation. The cerebellum cannot inhibit the movement. Therefore the movement goes beyond of the wished point.
3Lack of progression
The movement can begin too much soon or later. There is no progression of the movement. Confused movements take place.
4.Disartria
Lack of progression in the speech. The formation of words depends on a fast and ordered succession of the isolated muscular movements of the larynx. The lack of coordination among them and the incapacity to predict the intensity and the duration of the sounds are accompanied by a disordered speech, being some syllable intense, other ones weak, some ones long, other ones short and resulting a totally intelligible speech.
5.Temblor of action
It happens that the cerebellum cannot inhibit the motor effects. If a person has a cerebellum sickness, the conscious centers of the brain finishes realizing it and initiates a movement in opposite direction; but again the arm, due to inertia, go beyond the correct position and it will have to return to emit signals that tend to correct the error. . Therefore the arm oscillates around the right point during several cycles before reaching it.
6.Cerebellum nistagmo
Is an ocular globes tremor, usually it happens when it is wanted to fix a scene located to a side. This fixation of off-center type produces very fast movements in the eyes.
7.Rebote
When an arm is contracted and you hold on it. Once you release it, it will continue moving until something stop it (like a pendulum) the cerebellum when it is not altered, usually activates instantaneously and powerfully the reflection mechanisms of the spinal cord whenever a part of the body begins to move, in unexpected form and in an inadequate direction. If the cerebellum is altered, this activation of the antagonistic muscle does not take place and the member moves too much.
8.Hipotonía
Lost of motor tone of the peripheral muscle in the place of the injury.
LCR (cerebro spinal fluid)
Where the LCR is?.-- The LCR is in the ventricles of the brain, the cisterns that surround it, and in the subarachnoid space of the encephalo and the spinal cord. All these cavities are connected to each other and the pressure of the LCR is regulated to a constant pressure.
LCR function.-- Its function is to cushion the encephalon within its solid continent. Without the LCR any blow in the head would have repercussions in the encephalon and it could injure it seriously.
Where the LCR is formed? The LCR it is born constantly in the plexus surface. The plexus cells secrete actively NA's ions, which develop a load + in the LCR. This one attracts ions of charges-, especially ions of chloride. This way there is an excess of ions in the liquid of the ventricles. In consequence the osmotic pressure of the ventricular liquid rises up to approximately 160 mm of Hg higher than the one of the plasma and this osmotic force makes that big quantities of water and dissolved substances cross the membrane towards the LCR. Since the glucose is not dissolved with the water, its concentration is a little lower.
The low concentration of K depends on the transport of K in opposite direction across the ephitelial cells
The secretion intensity is almost 840 ml, which is approximately 5 times the total volume of the liquid of the whole cerebro spinal cavity
The surfaces of the ventricles are redressed in an epithelium called ependimo, and the LCR is in contact with all its points. Besides the LCR fills the subaracnoidal space between the pia mater who covers the encephalon and the subarachnoid membrane,
Therefore the LCR have a constant diffusion with the cerebral substance below the ependimo and also between (among) the LCR and the blood vessels of the meninges, specially the subarachnoid vessels.
LCR absorption.-- Almost the whole LCR formed every day is re-absorbed towards the blood following (continuing) special structures named hairinesses or aracnoideal granulations and often also in the veins of the spinal conduit.
LCR traffic.-- is formed in the lateral ventricles, goes towards the third ventricle crossing Monro's holes and circulates later for Silvio's aqueduct towards the fourth ventricle where produce more liquid. Then it continues up to the Magnum cistern crossing Luschaka's lateral holes and the hole of Magendie placed in the average line. From there it continues throughout the subaracnoideal spaces up to reaching the brain, where almost all the aracnoideal hairinesses are and empty in the venous bosoms.
LCR pressure. When a person is horizontally in bed, the LCR pressure is 130 mm of water (10 mm of Hg) though it can be as low as 70 mm of water and so high as 180 mm of water. LCR pressure is regulated by the intensity and resistance to the absorption of the aracnoideal hairinesses. When one of these factors increases, the pressure rises and when some factor diminishes pressure decrease.