Cerebellum

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The cerebellum or cerebellum is a part of the brain of vertebrates . There it is deposited on the back of the brain stem and is located below the occipital lobes of the cerebrum in the posterior fossa . Together with the elongated marrow ( myelencephalon ) and the bridge ( pons ) it forms the hindbrain ( rhombencephalon ). The cerebellum and the bridge are combined as the hindbrain ( metencephalon ).

In humans, the cerebellum is the second largest part of the brain by volume, but has a significantly higher cell density than the cerebrum. In adults, the human cerebellum, at around 150 g, only makes up around a tenth of the average brain weight, but with around 70  billion nerve cells it contains around four fifths, i.e. the majority of all central nervous neurons . The surface of the cerebellar cortex is folded into fine leaf-shaped coils ( folia cerebelli ) and corresponds to about 50–75% of the cortical surface of the eight times larger cerebral hemispheres.

The cerebellum fulfills important tasks in controlling the motor skills : It is responsible for coordination, fine-tuning, unconscious planning and the learning of movement sequences . In addition, it has recently been assigned a role in numerous higher cognitive processes.

location

Sagittal section of the brain (cortical sections of the cerebellum are numbered)

The cerebellum is located in the posterior fossa . It is superimposed on the brain stem ( midbrain , the bridge and the elongated medulla ) on the back ( dorsal ) and is connected to it via three cerebellar stalks ( pedunculus cerebellaris inferior , medius and superior ) on each side through which the fiber connections run. Thin structures made of white matter stretch upwards and downwards to the brain stem, the upper and lower medullary sail ( velum medullare superius and inferius , in animals craniale and caudale ).

Between the cerebellum and the brain stem, i.e. on the ventral side ( ventral ), bounded by the medulla oblongata and pons, laterally by the cerebellar stalks, dorsally by the marrow pelvis and the cerebellum, lies one of the cerebral cavities filled with liquor , the fourth ventricle , the floor of which is a diamond pit ( Fossa rhomboidea ) is called.

The cerebellum is separated from the cerebrum upwards (forwards in animals) from the cerebellar tent ( tentorium cerebelli ), a duplication of the dura mater , the occipital lobe of which lies directly above it (in front of it in animals). The cerebellum lies in the posterior cranial fossa, where it extends ventrally with the two processes known as the cerebellar tonsils to just before the foramen magnum .

In the area between the cerebellum and the lower edge of the pons in front of it ( cerebellar bridge angle ), the two cranial nerves, facial nerve and vestibulocochlear nerve , emerge obliquely anteriorly . Here, cerebellar bridge angle tumors ( acoustic neuromas ) can develop from the cover of the vestibulocochlear nerve .

construction

Schematic representation of the anatomical structure of the cerebellum. Top view of an "outstretched" cerebellar cortex

When cerebellum as in the cerebrum, the outwardly facing, is called nerve cell-containing layer as bark ( cortex ), which lies in the interior of white substance (only fiber connections, no cell bodies) as Mark ( medulla ). The accumulations of nerve cells found in the marrow are nuclei .

Macroscopically, the cerebellum is divided into two parts:

  • The worm ( vermis ) is a structure lying in the middle, about one to two centimeters wide, sagittal once all around,
  • the two hemispheres bulge out on either side of the worm. They are larger and wider than the worm in every direction.

In addition, at the bottom front, on the side facing the brainstem, starting from the worm, there is an arm-like extension on each side that ends as if with two paws. This is the flocculus , the adjacent together with the worm part, the nodule , for both functional and evolutionary clearly definable flocculonodular lobe is summarized.

The cerebellar cortex is clearly visible at regular intervals with almost parallel furrows running through it. Like the coils ( gyri ) of the cerebrum, they serve to increase the surface area, but they always run transversely (from left to right) and give the cerebellum its characteristic appearance. In cross-section, this unfolded arrangement resembles a tree ( arbor vitae , tree of life); accordingly, a section of bark protruding between two furrows is called folium (Latin for leaf ).

Both the worm and the hemispheres can, once walking around, be divided into numerous sections, which, however, have little functional meaning. Only the transversal division into an upper anterior lobe and a larger, lower posterior lobe is used more frequently.

Human cerebellum posterior view description.JPG
Top-back view of the cerebellum
A: Anterior lobe
B: Posterior lobe
C: Vermis
D: hemispheres
Human cerebellum anterior view description.JPG
Bottom-front view of the cerebellum
7: cerebellar tonsils
10: flocculus

In the medulla of the cerebellum, there are four nuclei on each side, from the inside out:

The dentate nuclei are much larger than the other nuclei and also the most recent in phylogenetic terms . Nucleus globosus and emboliformis are also referred to together as nucleus interpositus .

Types of nerve cells in the cortex

Hematoxylin - eosin -stained paraffin section of a human cerebellum. On the left in the picture the granular layer (dark dots = nuclei), on the right the molecular layer containing the extensions of the Purkinje cells , in between the Purkinje cell bodies
Purkinje cells in a sagittal cerebellar section. They express the GFP derivative EGFP under the control of the purkinje cell-specific promoter L7 and therefore fluoresce when excited with blue light
Moss fibers and their endings in the granular layer of the cerebellum. Marking of the moss fibers with Clomeleon, a fluorescent biosensor, expressed under the control of the Thy1 promoter, scale bar 20 μm
Scheme of the interconnection within the cerebellar cortex

The cortex can be divided into three layers, each of which contains a characteristic selection of the five different cell types:

  • Molecular layer , stratum molecularulare , completely outside
  • Purkinje cell layer , stratum purkinjense
  • Granular layer, stratum granulosum , inward

The typical cerebellar cell is the Purkinje cell , which is the only one that projects out of the cerebellar cortex. It inhibits the cerebellar nuclei, which in turn represent the central starting point for the entire cerebellum. It has a classic pear-shaped cell body with a basal axon and an apical primary dendrite that branches out like a tree. The branching of this dendrite tree is strictly aligned in one plane (tangential to the longitudinal axis of the folia), which is why the arrangement of the Purkinje cells is often compared to espalier fruit. The dendrites move far into the molecular layer to just below the surface of the cerebellum. They are extremely thorny (even stronger than the pyramidal cells of the cerebral cortex) and therefore form a large number of synaptic connections with other neurons inside and outside the cerebellum. It is the only calbindin- positive cell in the cerebellum.

The other typical cell of the cerebellar cortex is the granule cell , the only excitatory cell in the cerebellar cortex. The small, round cell bodies are dense and in large numbers in the granular layer. The axon runs up into the molecular layer, where it splits in a T-shape and runs as a parallel fiber along the cerebellar convolutions and thus vertically through the dendritic trees of the Purkinje cells. The unusual shape of the granule cell axon can be explained by its migration during development, which is described below. The basal dendrites of the granular cells form small plexuses in the granular layer with the basal axons of the Golgi cells, the glomeruli cerebellares , at which the extracerebellar moss fibers (see below ) also end.

The inhibitory interneurons of the cerebellar cortex are from basal to apical:

  • The Golgi cell lies next to the granule cell in the granular layer. Their axons move to the glomerula cerebellaria , where they inhibit the granule cells. In contrast to the Purkinje cell, its thorn-covered dendrite tree is bush-shaped and also extends into the molecular layer, where connections are made with the parallel fibers.
  • The basket cells lie deep in the molecular layer near the Purkinje cells, whose cell bodies they spin with their axons in order to inhibit the Purkinje cell at the initial segment of the axon . Their dendrites are connected to the collaterals of the Purkinje cells and to the parallel fibers . Each basket cell has an immense territory, so that one basket cell can inhibit about 70 Purkinje cells.
  • The stellate cells lie apically in the molecular layer and pull with their axons to the smooth (not thorny) dendritic sections of the Purkinje cells.

In addition to the processes of the cells of the cerebellum, there are two different types of fibers in the cerebellar cortex, both of which are exciting:

  • Moss fibers come from the spinal cord and many nuclei of the brain stem . They end at the glomerula cerebellaria , where they excite the granule cells and thus indirectly the Purkinje cells . The moss fibers get their name from their connection with the glomerula cerebellaria , which make the stratum granulosum of the cerebellar cortex appear like a moss-covered lawn in a microscopic image. They use glutamate as a transmitter.
  • Climbing fibers come from the lower olive complex and “climb” (hence the name) up the dendrite trees of the Purkinje cells, where they form exciting synaptic connections with the thorns of the dendrites. Some sources speak of aspartic acid as a transmitter, others of glutamate.

Interconnection

Scheme of the internal interconnection:
(+) excitatory synapse
(-) inhibitory synapse
ZKK central cerebellar nuclei
PjZ Purkinje cell
GgZ Golgi cell, KnZ granular cell
KbZ basket cell , StZ star cell
KF climbing fiber, MF moss fiber, PF parallel fiber

Despite the many different cell types, the wiring principle of the cerebellar cortex is relatively simple. The main task of the cerebellum is to fine-tune the motor skills, in other words to inhibit excessive “gross motor skills”. The information about the movement plan is conveyed to the cerebellar cortex via the climbing fibers and moss fibers (which also release collaterals to the cerebellar nuclei). The "results" of the cerebellar work are extracted from the cerebellum via the projections of the cerebellar nuclei.

The rough movement plan is brought to the Purkinje cell by the exciting climbing and moss fibers (here indirectly via the glomerula cerebellaria and the granule cells), whose task is now to inhibit excessive motor activity. The result is an absolute inhibition, i.e. no motor skills. Because of this, the Purkinje cell is now selectively inhibited by the Golgi cells, basket cells and stellate cells, so that a fine motor movement is now sent to the cerebellar nuclei and thus out of the cerebellum. In other words, the Purkinje cell is excited from outside and inhibits the cerebellar nuclei, whereby it itself is also selectively inhibited so that movement takes place at all.

In addition to the described classic interconnections of the bark, there are also monoaminergic afferents from the reticular formation , in particular with the transmitter serotonin from the raphe nuclei and with the transmitter noradrenaline from the locus caeruleus . They seem to have more modulatory tasks.

Glial cells in the cortex

In addition to the oligodendrocytes , astrocytes and microglia that are distributed throughout the CNS, there are also three special types of glial cells in the cerebellar cortex :

  • Wing astrocytes have wing- or blade-shaped appendages with which they surround the glomerula cerebellaria .
  • The Bergmann glia lies between the Purkinje cells in the stratum purkinjense . In the development of the cerebellum, these cells serve as a guide structure for the migrating neurons. In the adult cerebellum they form the membrana gliae limitans superficialis .
  • The pinnate glia of Fañanas , which are located in the molecular and purkinjense stratum and can only be shown histologically with a special gold color . A distinction is made between 3 types according to the number of runners: Fañanas cells with one, with two and with several runners.

Lanes

The inputs and outputs of the cerebellum are closely interwoven with the respective functions, which are discussed further below.

Afferents

The information necessary for the coordination and execution of movements comes from the spinal cord and brain stem:

  • Information about acceleration and the position of the head from the brain stem nuclei of the organ of equilibrium ( vestibulocerebellar tract )
  • Directly via the spinal cord, information about the position and position of the extremities of muscle spindles , joint receptors and Golgi tendon organs (cerebellar lateral cord tract, anterior and posterior spinocerebellar tract )
  • from the olive ( tractus olivocerebellaris ) information about the impulses of the motor cortex and other areas currently running to the muscles, about impulses sent by the cerebellum itself (feedback loop via the nucleus ruber , which projects to the olive) and about various information from the brain stem.

For the planning of movements and - if the hypotheses apply - also the implementation of numerous other cognitive processes, the cerebellum receives supplying fibers from the cortex (corticopontocerebellar tract). These afferents originate mainly from the frontal and temporal lobes, and to a small extent also from the parietal and occipital lobes. They run through the pons, which they essentially form with their fiber masses, cross over there on the opposite side, are switched in the scattered pontine nuclei and run through the broad central cerebellar stalk to their destination.

Detailed consideration
Rear view of the brain stem with the cerebellum severed. The upper (13), lower (14) and middle (15) cerebellar stalk are labeled.

The pontine afferents in their entirety form the pedunculus cerebellaris medius . The only afferent pathway is the anterior spinocerebellar tract in the superior cerebellar peduncles, all other afferents mentioned run in the lower cerebellar stalk.

In the vestibulocerebellar tract there are not only secondary fibers that have been switched in the vestibular nuclei, but also direct fibers from the organ of equilibrium. In addition to the flocculonodular lobe , parts of the orbit also end in the Ncl. fastigii and the uvula , part of the worm.

The anterior and posterior spinocerebellar tracts essentially only convey information from the lower extremity. There are two analogous paths for the upper extremity. Shares of the Hinterstrangbahn , which are in part of the Ncl. cuneatus in the brain stem, the Ncl. cuneatus accessorius , run as a tractus cuneocerebellaris to the cerebellum and correspond to the posterior cerebellar lateral tract . Analogous to the anterior tract, there is also a superior spinocerebellar tract from the cervical cord . The posterior path tends to guide high-resolution proprioception, the information from the anterior path tends to come from larger receptive fields.

Proprioception from the face extends from the trigeminal nuclei in the brain stem as the trigeminocerebellar tract to the cerebellum.

Efferents

All efferents emanate from the cerebellar nuclei (with the exception of a few direct pathways from the flocculonodular lobe to the vestibular nuclei). The cerebellum sends fibers to four brain regions:

All four pathways are important for controlling motor skills: The last three brain areas mentioned send their own pathways to the spinal cord. In addition, the above-mentioned feedback loop to the olive and back to the cerebellum runs through the nucleus ruber .

Basically, all of the pathways in the thalamus that go to the cerebral cortex are switched, including those of the cerebellum. The thalamus serves as an integration center for impulses from other motor centers ( basal ganglia , cortex itself) and leads the integrated pulses to the motor cortex areas , especially the cortex primary-motor on. It could be shown, however, that the cerebellar affinities are not restricted to motor cortex areas.

Detailed consideration

The pathway to the vestibular nuclei, the excitatory fibers from the Ncll. fastigii and - the only exception - also sends inhibitory fibers directly from the cortex of the flocculonodular lobe , runs in the lower cerebellar stalk. All other efferents run in the upper cerebellar stalk, then cross ( Decussatio pedunculorum cerebellarium superiorum , Wernekinck) and split into an ascending and a descending part.

The smaller, descending part runs to the reticular formation of the brain stem. The fibers come from the NcII. fastigii and globosi . In the ascending part, the pathways described above run to the thalamus, tractus cerebellothalamicus , and the projections to the Ncl. ruber , cerebellorubral tract .

The ones from the Ncll. Globosus and emboliformis parts of the cerebellorubral tract end in a part of the Ncl. ruber ( pars magnocellularis ), which itself sends descending tracts into the spinal cord directly and indirectly via the reticular formation . The parts of the cerebellorubral tract from the Ncl. dentatus end in the area ( pars parvocellularis ), which is connected to the olive stone via the central canopy and thus forms the above-mentioned feedback loop. The cerebellothalamic tract also arises from fibers from these three nuclei, Ncll. globosus , emboliformis and dentate .

structure

Simplified structure of the cerebellum with its afferents and efferents

The cerebellum can be divided into three to four sections according to various criteria. The most obvious is the classification according to anatomical sections. The functionally most important and most common distinction is that according to the afferents, in which the cerebellum is divided into three areas according to the origin of the feeding pathways:

  • The vestibulocerebellum , anatomically the flocculonodular lobe , is connected to the vestibular nuclei, the brain stem centers of the organ of equilibrium;
  • the spinocerebellum , anatomically the worm and adjacent areas, receive u. a. Information about body position from the spinal cord;
  • the pontocerebellum , anatomically corresponding to the lateral hemispheres, receives the fibers that come from the cerebrum via the bridge ( pons ).

The division according to phylogenesis , which is based on the phylogenetic development of the cerebellum, is often used synonymously :

  • The archicerebellum (corresponds to the vestibulocerebellum) is the oldest part of the cerebellum present in all vertebrates in evolutionary terms .
  • the paleocerebellum (corresponds to the spinocerebellum), represents the next evolutionary step associated with the development of limbs while
  • the neocerebellum (pontocerebellum) is due to the demands on complex movement processes and is only present in higher mammals or is unique in the extent and extent of the fiber connections in primates and then in humans.

Another possible criterion divides the cerebellum according to the cerebellar nuclei into which the respective sections project. This divides the spinocerebellum into two functionally different areas.

Even if the above-mentioned classifications are used synonymously according to the various criteria, the areas described are almost never completely congruent. The exception is the vestibulocerebellum - archicerebellum - flocculonodular lobe , where the agreement is largely present. In the other areas one can often only find an overlap of the order of eighty percent.

Afferents phylogenesis anatomy Efferents Anatomy (other direction)
Vestibulocerebellum Archicerebellum Flocculonodular lobe Nucleus fastigii and directly to the vestibular nuclei Flocculonodular lobe
Spinocerebellum Paleocerebellum Vermis Fastigii nucleus Anterior lobe
medial hemispheres (also paravermal or intermediate zone) Nucleus globosus and Nucleus emboliformis
Pontocerebellum Neocerebellum lateral hemispheres Dentate nucleus Posterior lobe

Blood supply

The cerebellum is supplied with blood via three paired arteries, these are from dorsal to frontal the arteria cerebelli posterior inferior (PICA) , the arteria cerebelli anterior inferior (AICA) and the arteria cerebelli superior (SCA) . The arteria cerebelli posterior inferior is the only one of the three to arise from the arteria vertebralis , it is also its largest branch. The arteria cerebelli anterior inferior and the arteria cerebelli superior are branches of the arteria basilaris . This approximately 3 to 3.5 cm long artery arises on the clivus of the skull base from the merger of the right and left vertebral arteries, for example in the transition area between the medulla oblongata and the pons.

Each artery initially controls a certain part of the cerebellum: The SCA arrives on the superior surface, the PICA posterior-inferior and frontal of this, i.e. anterior-inferior, the AICA. All location designations refer to the cerebellum itself, so the caudal part is controlled by two arteries, the cranial part by one. The branches of the three arteries finally anastomose in the pia mater and thus ensure the blood supply to the cerebellum.

function

Well-studied and widely recognized is the role of the cerebellum in planning, coordinating, and fine-tuning movements, with the different sections also performing different functions. The cerebellum is also assigned an important role in learning processes. In addition, theses about the role of the cerebellum in cognitive processes have been discussed for some time.

Motor skills

Vestibulocerebellum

This cerebellar part receives information about body position and movement from the equilibrium organ. He uses this on the one hand to control the holding and supporting motor skills. On the other hand, it is responsible for the fine-tuning of almost all eye movements that are generated by the various oculomotor centers in the brain stem.

Spinocerebellum

The spinocerebellum receives the afferents from the spinal cord, which provide information about the position of joints and muscles. It also receives continuous feedback about the movement signals sent to the spinal cord and thus to the periphery. It is divided into two functionally different zones according to the efferents. The vermis itself, which projects into the nucleus fastigii , is mainly responsible for standing, walking and supporting motor skills. The adjacent Hemisphere shares (intermediate zone projection in Nucleus globose and Nucleus emboliform ) are crucially involved in the target motor skills and movement execution . These components ensure that a movement proceeds as planned, hits its target exactly, and they ensure a comparison of efferents and afferents, i.e. that the commands sent correspond to the actual current position of the extremities and are constantly fine-tuned to the new position become. This also includes the extremely fine coordination of the facial and larynx muscles involved in speaking.

Pontocerebellum

The pontocerebellum (also cerebrocerebellum) is functionally connected to the cerebral cortex. It receives signals from many areas, especially the premotor centers in the frontal lobe ( premotor cortex and supplementary motor cortex ). There movement drafts, the planning of a movement arise. These rather rough drafts are sent to the lateral cerebellar hemispheres, where they are further developed, fine-tuned, modulated, corrected, compared with internal models derived from previous experience, and the planned activity of the muscles involved is coordinated. The feedback loop via the nucleus ruber and the olive back to the cerebellum also helps here . The results of these calculations go to the thalamus, where they (with the results of the other large subcortical motor center, the basal ganglia ) are integrated and passed on to the motor cortex.

Learning processes

The cerebellum plays a key role in implicit learning and thus in procedural memory . This means that well-trained, automated movement sequences can be called up without thinking, as their repetition has led to lasting changes in synaptic efficiency patterns in the cerebellum. Examples of this are the coordination of the facial muscles when speaking and the movement of fingers when writing or playing musical instruments, but also the coordination of the entire body such as when skiing or dancing.

The cerebellum is also a place of associative learning . The best studied example of this is the conditioning of the eyelid closing reflex , which z. B. plays a role in the insertion of contact lenses.

Cognitive processes

Since the 1980s there has been increasing discussion that the cerebellum is also involved in numerous cognitive processes. The following arguments are listed, among others:

  • The hemispheres of the cerebellum are more pronounced in humans than in any other species. In evolutionary terms, the growth of the cerebrum, in which the extraordinary cognitive abilities of humans are located, is directly associated with the growth of the hemispheres and the dentate nucleus .
  • The cerebellum receives an enormous amount of information through the pontine fibers. These strands comprise 200 million nerve fibers, while the optic nerve, for example, which brings information from the retina of the eye and thus occupies good parts of the cerebrum, only comprises around 1 million nerve fibers.
  • It was possible to show that the efferents of the cerebellum not only reach motor cortex areas, but also many other areas of the cortex.
  • There are cerebellar lesions in the area of ​​the posterior lobe that do not lead to any clinical abnormalities in the coordination of movements.
  • Functional examinations with modern imaging methods showed activation of the cerebellum in cognitive tasks.

According to another hypothesis, only the anterior lobe is really responsible for coordination of movements, while the lower vermis is believed to have an influence on affect and behavior. The left hemisphere (connected to the right cerebral hemisphere) plays a role in visuospatial thinking, the right hemisphere (connected to the left, language-dominant hemisphere) is important for speech functions. In line with this, dyslexia often correlates with impaired activity in the right cerebellar hemisphere. In contrast to speaking , which requires the coordination of the speech muscles, these are higher functions for language formation such as finding words. Both hemispheres are also generally assigned a role in the executive functions .

However, it is not yet clear how important the influence of the cerebellum actually is. The problem becomes clear with a few examples: In examinations with imaging methods, it is not possible to completely rule out cerebellar activity for movement coordination. The cerebellum is particularly active when speaking, making it difficult to make statements about language functions. There were also contradicting experiments. Cognitive changes can be demonstrated in patients with cerebellar lesions. However, these are never really serious and the question remains whether the motor deficits are not the real reason. In the case of really serious cerebellar lesions, a cognitive test is again almost impossible due to the severe motor deficits.

development

Development of the external form

Lateral-posterior brain stem of a three-month-old human fetus. The cerebellar plate (labeled "Cerebellum") arches over the cut open diamond pit ("Rhomboid fossa").
Brain of a five week old human embryo. The developing diamond lips (labeled “Rhombic lip”) can be seen above the bend of the bridge.

The cerebellum arises from the metencephalon , the fourth cerebral vesicle . Between the metencephalon and myelencephalon lies the lozenge pit, which was enlarged by the lowering of the bend in the sixth week . The anlage of the cerebellum develops at this point in the rostral part of the roof of the rhombus pit facing the mesencephalon. The very dorsolateral areas of the wing plate curve medially and form the diamond lips .

Caudally, the rhombus lips on both sides are separated from the cover plate, the very thin roof of the rhombus pit, but cranially they converge and unite directly below the mesencephalon.

Through further growth movements, lowering of the bend of the bridge, growth and bulging of the diamond lips in a dorsal direction, their shape changes to a transversely positioned plate, the cerebellar plate .

In a lateral direction, after twelve weeks, the vermis can be distinguished medially and the hemispheres laterally. First, the nodule and flocculus are separated longitudinally by a gap between the vermis and hemispheres. In the course of further growth, the remaining characteristic transverse furrows gradually appear.

Development of the bark

In the early stages, the cerebellar anus, like all other sections of the neural tube, consists of an internal neural epithelium with cells that are actively dividing, a mantle layer with proneurons that have emerged from the neural epithelium and migrated to the outside, and a marginal zone that mainly contains cell processes.

In the embryonic period, the first batch of cells migrates. The cerebellar nuclei arise from some of these cells in the mantle layer. The other part reaches the marginal zone and forms the outer granular layer there . This layer is typical of the development of the cerebellum. In contrast to the development of the other parts of the brain, their cells remain capable of dividing until after birth; in fact, new nerve cells develop here until the end of the second year of life.

Two important developmental steps occur in the fourth month. A second batch of cells migrates and reaches the outer granular layer , but remains on its inside. They are the precursors of the Purkinje cells. In addition, the differentiation of the outer granular layer now begins . From this cell-rich layer, the low-cell molecular layer, the outermost layer of the cerebellar cortex, with its basket and stellate cells, emerges after birth. But the cells of the outer granular layer also give rise to the granular cells, the cells of the inner granular layer .

Cell migration in the CNS normally occurs from the inside out, with the granule cell of the cerebellum being an important exception. It migrates tangentially below the surface of the cerebellum from the rhombus lip and forms an extension on each side that is parallel to the folium and thus perpendicular to the later dendritic tree of the Purkinje cells . Now it goes into connection with the extension of the so-called Bergmann glial cell , on which the other cells migrate from the inside to the outside, and climbs under the Purkinje cell layer, whereby the two extensions of the granule cell unite into one, which now gets a T-shape . This special histogenesis explains the unusual shape of the granule cell axon, the parallel fiber (from the granule cell up and then in a T-shape parallel to the folium). In many books one finds the statement that the axon would grow out of the granule cell layer upwards, but this statement is incorrect: Axons do not grow out, but arise through a migration of the respective neurons .

Pathophysiology

If the cerebellum is damaged or dysfunctional, a number of characteristic symptoms can occur, depending on the location and extent of the affected area. The most general name and umbrella term for most cerebellar symptoms is ataxia .

In detail, there may be:

  • for lesions of the vestibulocerebellum
    • nystagmus due to disturbance of the coordination of the eye movement
    • A trunk ataxia due to a lack of support motor skills , the inability to adequately perform the unconscious corrective movements of the trunk muscles necessary for standing and sitting;
  • with lesion of the median (vermalen) zone of the spinocerebellum
    • a stand and gait ataxia , an uncertain, wavering stance and gait as when drunk.
  • In the case of a lesion of the intermediate or paravermal zone of the spinocerebellum, the lack of control and coordination of movement execution is in the foreground, which is expressed by a number of symptoms:
    • Disorders of the target motor skills: with hypermetry over the target or with dysmetry hitting the target, z. B. when trying to hit the nose with your finger.
    • Closely related to this is the occurrence of an intention tremor, i.e. a tremor that becomes stronger the closer the hand comes to the goal. It is caused by non-coordinated and therefore excessive corrective movements.
    • The inability to perform antagonistic movements in quick succession and alternating is known as dysdiadochokinesis . The classic example is trying to quickly rotate the palm outward and inward.
    • After all, the lack of fine-tuning of the complex motor skills required for speaking causes a clinical picture known as dysarthria , which is characterized by unclear, slurred, sometimes incomprehensible language. But here only the speech motor skills are disturbed, not the higher language-understanding and -forming centers of the brain. Charcot describes the typical cerebellar language as "chanting".
  • The lesion of the pontocerebellum affects movement planning.
    • There may be a asynergy come in which not matched, the use of individual muscles on each other and thus is not synergistic. To compensate for this deficit, a sequence of movements can be decomposed into individual movements, so that, for example, first the shoulder joint is brought into the correct position, then the arm is stretched and only then the hand is moved instead of doing this in parallel in a flowing sequence.

The rhombencephalosynapsis is a rare malformation in which the two cerebellar hemispheres are fused and the worm is underdeveloped.

Web links

Commons : cerebellum ( cerebellum )  - collection of pictures, videos and audio files
Wikibooks: Topographic Anatomy: Neuroanatomy: Cerebellum  - Learning and Teaching Materials
Wiktionary: cerebellum  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Suzana Herculano-Houzel: The Human Brain in Numbers: A Linearly Scaled-up Primate Brain . In: Front Hum Neurosci . tape 3 , no. 31 , November 2009, p. 1–11 , doi : 10.3389 / neuro.09.031.2009 , PMC 2776484 (free full text).
  2. ↑ Line 11, Berglund et al. 2006, Brain Cell Biology 35, 207-235.
  3. ↑ Erhard Wischmeyer: Sensomotorik . In: Michael Gekle u. a. (Ed.): Pocket textbook Physiology . Thieme Verlag, Stuttgart 2010, ISBN 978-3-13-144981-8 , p. 747 f .
  4. ↑ Michael Schünke u. a .: Prometheus Learning Atlas of Anatomy. Head and neuroanatomy . 1st edition. Thieme Verlag, Stuttgart 2006, ISBN 978-3-13-139541-2 , p. 241 .
  5. ↑ Ulrich Welsch: Sobotta textbook histology . 2nd Edition. Urban & Fischer Verlag / Elsevier GmbH, Munich 2005, ISBN 978-3-437-42421-2 , p. 626 .
  6. ↑ Karl Uwe Petersen: On the fine structure of the neuroglial cells in the cerebellar cortex of mammals . In: Journal for Cell Research and Microscopic Anatomy . December 1969, p. 613-633 .
  7. ↑ Lakomy M: Glioarchitectonics of the cerebellar cortex and medulla of cows during postnatal development . In: Pol Arch Weter . 1980, p. 433-43 .
  8. ↑ Thompson, RF, Steinmetz, JE: The role of the cerebellum in classical conditioning of discrete behavioral responses. In: Neuroscience , 2009, 162nd Jg., No. 3, pp. 732-755.