Cerebellum

Cross references:     Posterior Horn of the Spinal Cord     
Cerebellar Afferent Pathways   
 
 
Cerebellar Efferent Pathways      
Cerebellum Tonic Inhibition       Deep Cerebellar Nuclei   

Cerebellar Neurotransmitters     Motor Programs         Dictionary  


Cerebellum (Wiki)   
    "The cerebellum (Latin for little brain) is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses,[1] but its movement-related functions are the most solidly established.  
    The cerebellum does not initiate movement, but it contributes to coordination, precision, and accurate timing. It receives input from sensory systems and from other parts of the brain and spinal cord, and integrates these inputs to fine tune motor activity.[2]  
    Because of this fine-tuning function, damage to the cerebellum does not cause paralysis, but instead produces disorders in fine movement, equilibrium, posture, and motor learning.[2]
"  
    Summary
"It receives input from sensory systems and from other parts of the brain and spinal cord, and integrates these inputs to fine tune motor activity.[2]   "  

Gray677.png
Drawing of the human brain, showing cerebellum and pons facing to the right. 



Part of Metencephalon

Cerebellum and surrounding regions;
sagittal view of one hemisphere facing to the left.

Click the links for much more info. 

A: Midbrain.
B: Pons.
C: Medulla.
D: Spinal cord.
E: Fourth ventricle.
F: Arbor vitae.
G: Tonsil.
H: Anterior lobe.
 I: Posterior lobe.

    "In terms of anatomy, the cerebellum has the appearance of a separate structure attached to the bottom of the brain, tucked underneath the cerebral hemispheres.  
    The surface of the cerebellum is covered with finely spaced parallel grooves, in striking contrast to the broad irregular convolutions of the cerebral cortex. These parallel grooves conceal the fact that the cerebellum is actually a continuous thin layer of tissue (the cerebellar cortex), tightly folded in the style of an accordion.  
    Within this thin layer are several types of neurons with a highly regular arrangement, the most important being Purkinje cells and granule cells.  
    This complex neural network gives rise to a massive signal-processing capability, but almost all of its output is directed to a set of small 
Deep Cerebellar Nuclei  lying in the interior of the cerebellum."  
    "In addition to its direct role in motor control, the cerebellum also is necessary for several types of motor learning
"  
    "
Anatomists classify the cerebellum as part of the metencephalon, which also includes the pons; the metencephalon is the upper part of the rhombencephalon or "hindbrain".  
    Like the cerebral cortex, the cerebellum is divided into two hemispheres; it also contains a narrow midline zone called the vermis. A set of large folds is, by convention, used to divide the overall structure into 10 smaller "lobules". Because of its large number of tiny granule cells, the cerebellum contains more neurons than the rest of the brain put together, but it takes up only 10% of total brain volume.[4]
"  
    "
Underneath the gray matter of the cortex lies white matter, made up largely of myelinated nerve fibers running to and from the cortex. Embedded within the white matter — which is sometimes called the arbor vitae (Tree of Life) because of its branched, tree-like appearance in cross-section — are four   Deep Cerebellar Nuclei  , composed of gray matter.[3]
"  
    "
Based on surface appearance, three lobes can be distinguished in the cerebellum, called the flocculonodular lobe, anterior lobe (above the primary fissure), and posterior lobe (below the primary fissure). These lobes divide the cerebellum from rostral to caudal (in humans, top to bottom).  
    In terms of function, however, there is a more important distinction along the medial-to-lateral dimension. Leaving out the flocculonodular part, which has distinct connections and functions, the cerebellum can be parsed functionally into a medial sector called the spinocerebellum and a larger lateral sector called the cerebrocerebellum.[3]
    A narrow strip of protruding tissue along the midline is called the vermis (Latin for "worm").[3]
"  
  
Schematic representation of the major anatomical subdivisions of the cerebellum. Superior view of an "unrolled" cerebellum, placing the vermis in one plane. 
                                                                                                                        
NOTE:  In the diagram, above, the dotted lines indicate the boundary between the
spinocerebellum
, along the midline, and the cerebrocerebellum, along the sides. 

    "
The smallest region, the flocculonodular lobe, is often called the vestibulocerebellum. It is the oldest part in evolutionary terms (archicerebellum) and participates mainly in balance and spatial orientation; its primary connections are with the vestibular nuclei, although it also receives visual and other sensory input. Damage to it causes disturbances of balance and gait.[3]
"  
    "
The medial zone of the anterior and posterior lobes constitutes the spinocerebellum, also known as paleocerebellum. This sector of the cerebellum functions mainly to fine-tune body and limb movements. It receives proprioception input from the dorsal columns of the spinal cord (including the spinocerebellar tract) and from the trigeminal nerve, as well as from visual and auditory systems. It sends fibres to 

Deep Cerebellar Nuclei   that, in turn, project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems.[3]
"  
    "
The lateral zone, which in humans is by far the largest part, constitutes the cerebrocerebellum, also known as neocerebellum. It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming cortico-ponto-cerebellar pathways), and sends output mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus.[3]
"  
    "
There is disagreement about the best way to describe the functions of the lateral cerebellum: It is thought to be involved in planning movement that is about to occur,[5] in evaluating sensory information for action,[3] and in a number of purely cognitive functions as well.[6]
"  
    "
There is considerable evidence that the cerebellum plays an essential role in some types of motor learning. The tasks where the cerebellum most clearly comes into play are those in which it is necessary to make fine adjustments to the way an action is performed. There has, however, been much dispute about whether learning takes place within the cerebellum itself, or whether it merely serves to provide signals that promote learning in other brain structures.[17]
"  
    Important points
1.  "
This complex neural network gives rise to a massive signal-processing capability, but almost all of its output is directed to a set of small   Deep Cerebellar Nuclei   lying in the interior of the cerebellum.
2. 
"The medial zone ... sends fibres to deep cerebellar nuclei that, in turn, project to both the cerebral cortex and the brain stem ... " 
3. 
"The lateral zone receives input exclusively from the cerebral cortex ... and sends output mainly to the ventrolateral thalamus ...
4.  Doesn't specify either the efferent path or the efferent neurotransmitter, so they could be either excitatory or inhibitory. 


Anatomy of the cerebellum - Wikipedia   
https://en.wikipedia.org/wiki/Anatomy_of_the_cerebellum  
    "
The anatomy of the cerebellum can be viewed at three levels. At the level of gross anatomy, the cerebellum consists of a tightly folded and crumpled layer of cortex, with white matter underneath, several deep nuclei embedded in the white matter, and a fluid-filled ventricle in the middle. At the intermediate level, the cerebellum and its auxiliary structures can be broken down into several hundred or thousand independently functioning modules or "microzones". At the microscopic level, each module consists of the same small set of neuronal elements, laid out with a highly stereotyped geometry.

Contents





    "The cerebellum can also be divided in three parts based on both phylogenetic criteria (the evolutionary age of each part) and on functional criteria (the incoming and outgoing connections each part has and the role played in normal cerebellar function). From the phylogenetically oldest to the newest, the three parts are:"  



Functional denomination (phylogenetic denomination) Anatomical parts         Role

Vestibulocerebellum (Archicerebellum)

Flocculonodular lobe (and immediately adjacent vermis)

The vestibulocerebellum regulates balance and eye movements. It receives vestibular input from both the semicircular canals and from the vestibular nuclei, and sends fibres back to the medial and lateral vestibular nuclei. It also receives visual input from the superior colliculi and from the visual cortex (the latter via the pontine nuclei, forming a cortico-ponto-cerebellar pathway). Lesions of the vestibulocerebellum cause disturbances of balance and gait.

Spinocerebellum (Paleocerebellum)

Vermis and intermediate parts of the hemispheres ("paravermis")

The spinocerebellum regulates body and limb movements. It receives proprioception input from the dorsal columns of the spinal cord (including the spinocerebellar tract) and the trigeminal nerve, as well as from visual and auditory systems. It sends fibres to deep cerebellar nuclei which in turn project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems. The spinocerebellum contains sensory maps as it receives data on the position of various body parts in space: in particular, the vermis receives fibres from the trunk and proximal portions of limbs, while the intermediate parts of the hemispheres receive fibres from the distal portions of limbs. The spinocerebellum is able to elaborate proprioceptive input in order to anticipate the future position of a body part during the course of a movement, in a "feed forward" manner.

Cerebrocerebellum (Neocerebellum, Pontocerebellum)

Lateral parts of the hemispheres

The neocerebellum is involved in planning movement and evaluating sensory information for action. It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming cortico-ponto-cerebellar pathways), and sends fibres mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus (in turn connected to the inferior olivary nucleus, which links back to the cerebellar hemispheres). The neocerebellum is involved in planning movement that is about to occur[4] and has purely cognitive functions as well.


Deep cerebellar nuclei - Wikipedia 
https://en.wikipedia.org/wiki/Deep_cerebellar_nuclei    
    "The cerebellum has four deep cerebellar nuclei embedded in the white matter in its center.  
The four deep nuclei of the cerebellum are the dentate, emboliform, globose, and fastigii nuclei and they act as the main centers of communication, sending and receiving information to and from specific parts of the brain. In addition, these nuclei receive both inhibitory and excitatory signals from other parts of the brain which in turn affect the nuclei's outgoing signals.[5](The globose and the emboliform nuclei make up the interposed nucleus).

    1 Inputs

    These nuclei receive inhibitory (GABAergic) inputs from Purkinje cells in the cerebellar cortex and excitatory (glutamatergic) inputs from mossy fiber and climbing fiber pathways. Most output fibers of the cerebellum originate from these nuclei. One exception is that fibers from the flocculonodular lobe synapse directly on vestibular nuclei without first passing through the deep cerebellar nuclei. The vestibular nuclei in the brainstem are analogous structures to the deep nuclei, since they receive both mossy fiber and Purkinje cell inputs.[citation needed]

    2 Specific nuclei

    From lateral to medial, the four deep cerebellar nuclei are the dentate, emboliform, globose, and fastigii. Some animals, including humans, do not have distinct emboliform and globose nuclei, instead having a single, fused interposed nucleus. In animals with distinct emboliform and globose nuclei, the term interposed nucleus is often used to refer collectively to these two nuclei. 
    See:   Deep Cerebellar Nuclei 

    3 Topography
   
In general, each pair of deep nuclei is associated with a corresponding region of cerebellar surface anatomy. 


Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+) and inhibitory synapses by (-). 

File:CerebCircuit.png

MF: Mossy fiber.
DCN: Deep cerebellar nuclei.
IO: Inferior olive.
CF: Climbing fiber.
GC: Granule cell.
PF: Parallel fiber.
PC: Purkinje cell.
GgC: Golgi cell.
SC: Stellate cell.
BC: Basket cell

  • The dentate nuclei are deep within the lateral hemispheres,
  • the interposed nuclei are located in the paravermal (intermediate) zone,
  • and the fastigial nuclei are in the vermis.
These structural relationships are generally maintained in the neuronal connections between the nuclei and associated cerebellar cortex, with the dentate nucleus receiving most of its connections from the lateral hemispheres,
  • the interposed nuclei receiving inputs mostly from the paravermis,and the fastigial nucleus receiving primarily afferents from the vermis. 


  • Differential GABAergic and glycinergic inputs of inhibitory interneurons and Purkinje cells to principal cells of the cerebellar nuclei.
    https://www.ncbi.nlm.nih.gov/pubmed/25009273
        "
    The principal neurons of the cerebellar nuclei (CN), the sole output of the olivo-cerebellar system, receive a massive inhibitory input from Purkinje cells (PCs) of the cerebellar cortex. Morphological evidence suggests that CN principal cells are also contacted by inhibitory interneurons, but the properties of this connection are unknown.  
        Using transgenic, tracing, and immunohistochemical approaches in mice, we show that CN interneurons form a large heterogeneous population with GABA/glycinergic phenotypes, distinct from GABAergic olive-projecting neurons. CN interneurons are found to contact principal output neurons, via glycine receptor (GlyR)-enriched synapses, virtually devoid of the main GABA receptor (GABAR) subunits α1 and γ2. Those clusters account for 5% of the total number of inhibitory receptor clusters on principal neurons.  
        Brief optogenetic stimulations of CN interneurons, through selective expression of channelrhodopsin 2 after viral-mediated transfection of the flexed gene in GlyT2-Cre transgenic mice, evoked fast IPSCs in principal cells. GlyR activation accounted for 15% of interneuron IPSC amplitude, while the remaining current was mediated by activation of GABAR. Surprisingly, small GlyR clusters were also found at PC synapses onto principal CN neurons in addition to α1 and γ2 GABAR subunits. However, GlyR activation was found to account for <3% of the PC inhibitory synaptic currents evoked by electrical stimulation.  
        This work establishes CN glycinergic neurons as a significant source of inhibition to CN principal cells, forming contacts molecularly distinct from, but functionally similar to, Purkinje cell synapses. Their impact on CN output, motor learning, and motor execution deserves further investigation. "  
       
    Free full text   
    http://www.jneurosci.org/content/34/28/9418.long   
          


    The cerebellum 
    http://bio.sunyorange.edu/updated2/comparative_anatomy/anat.html2/n_CEREBELLUM.htm  
        Long article with many pictures available online for free.  Click on the link above to see it all. 

    "

         The cerebellum is the second largest region of the human brain.  It coordinates motor output, measures body position and balance, and may have a variety of additional roles as well.  The most primitive cerebellums evolved in the first vertebrates.

         The existence of a cerebellum in hagfish and lampreys has been debated.   Some conclude that hagfish possess a very poorly developed cerebellum while others feel that this brain region is completely absent (Butler, 1996; Nieuwenhuys, 2002).  Lampreys possess a simple cerebellum, although they lack Purkinje fibers and cerebellar nuclei.  The cells of the cerebellar cortex are organized in a way similar to those of higher vertebrates with an outer layer of large cells, which may be the precursors to the Purkinje cells of gnathostomes and an inner layer of small cells (Ariens, p. 707; Murakami, 2005).  Lampreys possess a number of cerebellar connections which are also present in gnathostomes including bulbocerebellar, crossed and uncrossed tectocerebellar, cerebellotectal, cerebellotoral, and bello-tegmental connections and the tractus lobo-cerebellaris.   The vestibular nerve projects to the cerebellum in lampreys; in higher vertebrates this nerve enables the cerebellum to measure balance (Ariens, p. 708).


    LAMPREY

    LAMPREY CEREBELLUM






    DRAWING
    "  

       
      

    From:  THE BRAIN FROM TOP TO BOTTOM 
    http://thebrain.mcgill.ca/flash/d/d_06/d_06_cl/d_06_cl_mou/d_06_cl_mou.html    
    http://thebrain.mcgill.ca/flash/a/a_06/a_06_cl/a_06_cl_mou/a_06_cl_mou.html  
    http://thebrain.mcgill.ca/flash/a/a_06/a_06_cr/a_06_cr_mou/a_06_cr_mou.html   


    From: 
    Brain of the Tiger Salamander     

    XII. Cerebellum    
       
    Figure Descriptions    
       
    Figure Abbreviations   
       
    Figure Labels    


    See also: 
       
    Neuroscience  and  Human Neuroanatomy   

     

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