CEREBELLUM: STRUCTURE, FUNCTIONS AND ANATOMY (WITH PICTURES) - NEUROPSYCHOLOGY - 2024

The human cerebellum is one of the largest brain structures that is part of the nervous system. It represents approximately 10% of brain weight and can contain approximately more than half of the brain's neurons.

Traditionally, it has been attributed a prominent role in the execution and coordination of motor acts and the maintenance of muscle tone for balance control, due to its position close to the main motor and sensory pathways.

Cerebellum in blue color

However, over the last few decades, clinical neuroscience has considerably expanded the traditional view of the cerebellum as a mere coordinator of motor functions.

The current research interest is focused on the participation of the cerebellum in complex cognitive processes, such as executive functions, learning, memory, visuospatial functions or even contributing to the emotional sphere and the linguistic area.

This new vision of the functioning of the cerebellum is based on the detailed study of its structure, and in addition to the analysis of injury studies in both animals and humans through different current neuroimaging techniques.

Anatomy

Location

This broad structure is located caudally, at the level of the brainstem, below the occipital lobe and is supported by three cerebellar peduncles (superior, middle and inferior) through which it connects with the brainstem and the rest of the structures. encephalic.

External structure

The cerebellum, like the brain, is covered in its entire external extension by a highly folded cortex or cerebellar cortex.

With respect to the external structure, there are different classifications based on their morphology, functions or phylogenetic origin. In general, the cerebellum is divided into two main portions.

In the middle line is the vermis that divides it and connects the two lateral lobes, or cerebellar hemispheres (right and left). In addition, the lateral extensions of the vermis in turn are divided into 10 lobes numbered from I to X, being the most superior. These lobes can be grouped into:

• Anterior lobe: lobes IV.
• Upper posterior lobe: VI-VII
• Lower posterior lobe: VIII-IX
• Flocculonodular lobe: X.

In addition to this classification, recent research suggests a division of the cerebellum based on the different functions it modulates. One of the schemes is the one proposed by Timman et al., (2010), which hypothetically assigns cognitive functions to the lateral area, motor functions to the intermediate area, and emotional functions to the medial area of ​​the cerebellum.

Internal structure

Surface of the cerebellum.

Regarding the internal structure, the cerebellum cortex presents a uniform cytoarchitectural organization throughout the entire structure and is composed of three layers:

Molecular or outer layer

Stellate cells and basket cells are found in this layer, in addition to the dendritic treeizations of Punkinje cells and parallel fibers.

Stellate cells synapse with the dendrites of Punkinje cells and receive stimuli from parallel fibers. On the other hand, the basket cells extend their axons above the Purkinje cell somes, emitting branches on them and also receive stimuli from the parallel fibers. In this layer there are also the dendrites of Golgi cells whose somas are located in the granular layer.

Purkinje Cell or intermediate layer

It is formed by the somas of the Purkinje cells, whose dendrites are found in the molecular layer and their axons are directed towards the granular layer through the deep nuclei of the cerebellum. These cells are the main exit route to the cerebral cortex.

Granular or inner layer

It is composed mainly of granualar cells and some Golgi interneurons. The granule cells extend their axons into the molecular layer, where they bifurcate to form parallel fibers. In addition, this layer is a pathway for information from the brain through two types of fibers: mossy and climbing.

In addition to the cortex, the cerebellum is also made up of a white substance inside, within which four pairs of deep cerebellar nuclei are located: fastigial, globose, emboliform and dentate nuclei. Through these nuclei the cerebellum sends its projections outwards.

• Fastigial nucleus: receives projections from the medial region of the cerebellum, the vermis.
• Interposing nucleus (globose and emboliform): receives projections from the contiguous regions of the vermis (paravermal or paravermis region).
• Dentate nucleus: receives projections from the cerebellar hemispheres.

Cerebellar afferents and efferences

Information reaches the cerebellum from different points of the nervous system: cerebral cortex, brain stem and spinal cord, and also, it is accessed mainly through the middle peduncle and to a lesser extent through the lower one.

Almost all the afferent pathways of the cerebellum end in the granular layer of the cortex in the form of mossy fibers. This type of fiber constitutes the main input of information to the cerebellum and originates in nuclei of the brainstem and synapses with the dendrites of Purkinje cells.

However, the inferior olivary nucleus spreads its projections through the climbing fibers that synapse with the dendrites of the granule cells.

In addition, the main route of information exit from the cerebellum runs through the deep nuclei of the cerebellum. These extend their projections to the superior cerebellar peduncle that will project both areas of the cerebral cortex and motor centers of the brainstem.

Functions of the cerebellum

As we have noted, initially, the role of the cerebellum was highlighted due to its motor involvement. However, recent research offers different evidences on the possible contribution of this structure to non-motor functions.

These include cognition, emotion, or behavior; functioning as a coordinator of cognitive and emotional processes, since this structure has broad connections with cortical and subcortical regions that are not directed only towards motor areas.

Cerebellum and motor functions

The cerebellum stands out as a coordination and organization center for movement. Together, it works by comparing orders and motor responses.

Through its connections it receives the motor information elaborated at the cortical level and the execution of the motor plans and is in charge of comparing and correcting the development and evolution of motor acts. In addition, it also acts by reinforcing movement to maintain adequate muscle tone when changing position.

Clinical studies examining cerebellar pathologies have consistently shown that patients with cerebellar disorders have disorders that produce motor syndromes, such as cerebellar ataxia, which is characterized by lack of coordination of balance, gait, limb movement and of the eyes and dysarthria among other symptoms.

On the other hand, a large number of studies in humans and animals provide ample evidence that the cerebellum is involved in a specific form of associative motor learning, classical blink conditioning. Specifically, the role of the cerebellum in learning motor sequences is highlighted.

Cerebellum and cognition

Cerebellum in yellow color

Starting in the eighties, several anatomical and experimental studies with animals, patients with cerebellar damage, and neuroimaging studies suggest that the cerebellum has broader functions, involved in cognition.

The cognitive role of the cerebellum, therefore, would be related to the existence of anatomical connections between the brain and the regions of the cerebellum that support higher functions.

Studies with injured patients show that many cognitive functions are affected, associated with a wide spectrum of symptoms such as impaired attentional processes, executive dysfunctions, visual and spatial disturbances, learning and a variety of language disorders.

In this context, Shamanhnn et al (1998) proposed a syndrome that would encompass these non-motor symptoms that patients with focal cerebellar damage presented, called affective cognitive cerebellar syndrome (ACS), which would include deficiencies in executive function, visual-spatial skills, language skills, affective disturbance, disinhibition or psychotic characteristics.

Specifically, Schmahmann (2004) proposes that motor symptoms or syndromes appear when cerebellar pathology affects sensorimotor areas and SCCA syndrome when the pathology affects the posterior part of the lateral hemispheres (which participates in cognitive processing) or in the vermis (which participates in emotional regulation).

Cerebellum and emotional area

Due to its connections, the cerebellum can participate in neural circuits that play a prominent role in emotional regulation and autonomic functions.

Different anatomical and physiological studies have described reciprocal connections between the cerebellum and the hypothalamus, the thalamus, the reticular system, the limbic system, and areas of neocortical association.

Timmann et al. (2009) in their research found that the vermis maintained connections with the limbic system, including the amygdala and the hippocampus, which would explain its relationship with fear. This coincides with the findings raised a few years ago by Snider and Maiti (1976), which demonstrated the relationship of the cerebellum with the Papez circuit.

In sum, human and animal studies provide evidence that the cerebellum contributes to associative emotional learning. The vermis contributes to the autonomic and somatic aspects of fear, while the postero-lateral hemispheres may play a role in emotional content.

References

1. Delgado-García, JM (2001). Structure and function of the cerebellum. Rev Neurol, 33 (7), 635-642.
2. Mariën, P., Baillieux, H., De Smet, H., Engelborghs, S., Wilssens, I., Paquier, P., & De Deyn, P. (2009). Cognitive, linguistic and affective disturbances following a right superior cerebellar artery infarction: A cada study. Cortex, 45, 537-536.
3. Mediavilla, C., Molina, F., & Puerto, A. (1996). Non-motor functions of the cerebellum. Psicothema, 8 (3), 669-683.
4. Philips, J., Hewedi, D., Eissa, A., & Moustafa, A. (2015). The Cerebellum and psychiatric disorders. Frontiers in Public Heath, 3 (68).
5. Schamahmann, J. (2004). Disorders of the Cerebellum: Ataxia, Dysmetria of Thoght, and the Cerebellar Cognitive Affective Syndrome. The journal of Neurpsychiatry and Clinical Neurosciences, 16, 367-378.
6. Timan, D., Drepper, J., Frings, M., Maschke, M., Richter, S., Gerwing M., & Kolb, FP (2010). The human cerebellum contributes to motor, emotional and cognitive associative learning. To reiew. Cortex, 46, 845-857.
7. Tirapu-Ustárroz, J., Luna-Lario, P., Iglesias-Fernández, MD, & Hernáez-Goñi, P. (2011). Contribution of the cerebellum to cognitive processes: current advances. Journal of Neurology, 301, 15.