The human brain is a perfect machine because it can perform many critical functions of the body. The development of the human brain has helped individuals to be the most advanced beings on the planet. The brain is part of the Nervous System, divided into several sections, and the cerebellum is one of the most important: One of the largest brain assemblies within the Nervous System.
Picture 1: Schematic diagram of Cerebellum
Cerebellum embodies for approximately 10% of the brain weight, and it contains approximately more than half of neurons. Conventionally, cerebellum has been attributed a prominent role in the execution and coordination of motor actions, and the muscle tone for balance control preservation, due to its location close to the key motor and sensory pathways. However, over the last decades, clinical neuroscience has considerably broadened the traditional view of the cerebellum as a measly coordinator of motor functions.
Where is Cerebellum located?
The cerebellum is named the silent area of the brain. The cerebellum is a voluminous nervous mass that weighs 140 grams. It is located in the back and bottom of the cranium base. It has ovoid shape, slightly flattened, and a central recess. The cerebellum monitors and establishes corrective adjustments of motor activities triggered by other parts of the brain. The cerebellum continually receives current information from the peripheral parts of the body, to determine the instantaneous state of each area. The cerebellum compares the current physical state of each part of the body, as sensory information indicates, with the state attempting to produce the motor system.
Picture 1: Location of Cerebellum
The cerebellum is located at the level of the brainstem, under the occipital lobe. It is supported by three cerebellar peduncles (upper, middle and lower), through which Cerebellum links with the brainstem and the others encephalic structures. The peduncles are cylinders of white matter that connect the bulb, the bulge, the cerebellum and the brain.
The cerebellum is covered by a cortex, highly folded. Regarding the external structure, there are different classifications depending on the morphology, functions or phylogenetic origin. In general, the cerebellum is divided into two main regions. The vermis is in the middle line, dividing the cerebellum, and connects the two lateral lobes, or cerebellar hemispheres (right and left). In addition, the lateral extensions of vermis are divided into 10 lobes, numbered from I to X. These lobes can be grouped into: Anterior lobe: lobes I-V. Upper posterior lobe: VI-VII. Lower. Posterior lobe: VIII-IX. Flocculonodular lobe: X.
In addition to this classification, recent scientific research suggests a division of the cerebellum based on the different functions it can modulate. We talk about significant cognitive functions in the lateral area, motor functions in the intermediate area, and emotional functions in the medial area of the cerebellum.
Picture 3: Internal Structure of Cerebellum
Regarding the internal structure, the cortex of the cerebellum is organized in a uniform cytoarchitectonic way, molded by three layers:
- The molecular or outer layer, where there are star cells and basket cells, in addition to the dendritic arborizations of the Purkinje cells, and the parallel fibers. The stellate cells establish synapses with the dendrites of the Purkinje cells, and receive stimuli from the parallel fibers. On the other hand, the basket cells extend their axons above the Purkinje cellular directive, emitting ramifications, and also receive stimuli of the parallel fibers. In this layer we find also the dendrites of the Golgi cells, located in the granular layer.
- Purkinje or intermediate cell layer, is formed by the sums of the Purkinje cells, whose dendrites are in the molecular layer, and their axons are directed towards the granular layer through the deep nuclei of the cerebellum. These cells constitute the main route of exit towards the cerebral cortex.
- Granular or internal layer is composed mainly of granular cells, and some Golgi interneurons. The granular cells extend their axons towards the molecular layer, where they branch out to form the parallel fibers. In addition, this layer is a way of accessing information from the brain through climbing and mossy fibers.
In addition to the cortex, the cerebellum is also composed of a white substance inside, within which are located four pairs of deep cerebellar nuclei: fastigial nucleus, emboliform and globose nuclei, and dentate nucleus. Through these nuclei the cerebellum sends its projections outwards.
- Fastigial core: Receives projections of the medial region of the cerebellum, the vermis.
- Interposed core (globose and emboliform nucleus): It receives projections of the regions contiguous to vermis (paravermal region or paravermis).
- Toothed nucleus: Receives projections of the cerebellar hemispheres.
The function of the cerebellum is to guide and coordinate the body movement and stance. Cerebellum is located behind the right brain stem, in lower brain area. It has a large mass from the anterior cerebral cortex, and a portion of the brain stem. The cerebellum is divided into two hemispheres, and a cortex surrounding these hemispheres.
The main function of the cerebellum is to organize the complex information received by the brain. The cerebellum collects the information from the inner ear, the sensory nerves and the visual auditory structure. The cerebellum also coordinates motor movements and simple memory and learning processes. The cerebellum stands out for being a center of coordination and organization of the movement. It works by comparing orders and motor responses. Through its connections, the cerebellum receives the motor information elaborated at cortical level, comparing and correcting the development and evolution of the motor acts. In addition, cerebellum also works by strengthening the movement to maintain a proper muscular tone, adequate to the changes of posture.
Through its connections, the cerebellum participates in the neural circuits that have a prominent role in the emotional regulation and the autonomic functions. Different anatomical and physiological contrasts have succeeded in describing reciprocal connections between the cerebellum and the hypothalamus, the thalamus, the reticular system, the limbic system, and the neocortical association areas. Recent researches has shown that the vermis has connections with the limbic system, including the amygdala and hippocampus, which may explain the relation with the fear feeling.
The cognitive role of the cerebellum is related to the existence of anatomical connections between the brain and cerebellum regions that support the higher functions. Studies with injured patients show that many cognitive functions are affected, associating with a wide spectrum of symptoms, such as impairment of attentional processes, executive dysfunctions visual, and spatial alterations, learning a variety of language disorders.
Prestigious scientific research discovered a syndrome that encompassed those non-motor symptoms in patients with cerebellar focal damage: The Cerebellar Cognitive Affective Syndrome, which includes deficiencies in executive function, visual-spatial skills, language skills, affective disturbance, disinhibition or psychotic disorders. Symptoms or motor syndromes appear when cerebellar pathology affects sensory-motor areas, whereas Cognitive Affective Cerebellar Syndrome affects the posterior part of the lateral hemispheres (involved in cognitive processing) or vermis (which participates in regulation emotional).
In addition to the functions described above, the cerebellum is also responsible for coordinating voluntary motor movements, balance and muscle tone. If a traumatic brain injury, or a serious illness (such as brain cancer) occurs, the function of the cerebellum can be damaged. Damage to the cerebellum causes movements to be slow and uncoordinated. Therefore, people with cerebellar lesions sway and stagger as they walk. Cerebellar damage can lead to even greater problems in an individual. We can check some examples about it:
- Ataxic dysarthria: The advance in difficulty speaking.
- Asynergy: Problems in the coordination and motor movement.
- Dysmetria: The individual has difficulty calculating distance and when he/she should stop.
- Hypotonia: The individual suffers from weak muscles.
- The ataxic gait: The shake and the sway when individual is walking.
- The tremor of intention: Tremor in individual, that may lead to several movements.
- Nystagmus: There is an irregular eyes movement.
More recent research has shown that cerebellar pathology may be associated with damage mainly in the cognitive domain rather than motor performance. On the other hand, studies have also shown that the cerebellum is involved in many psychiatric diseases such as schizophrenia, bipolar disorder or autism.