Synonyms
Medical: Cerebellum (lat.)
Introduction
The very fact that the cerebellum contains nerve cells that have an inhibitory effect allows us to understand its function to a certain extent. The cerebellum serves – to put it very succinctly at the beginning – to control movement sequences, primarily to limit movements so that they are regulated and do not become excessive.
Pontocerebellum
The cerebral cortex is responsible for planning movements. It sends information to the basal ganglia and – via a detour via the bridge (pons) – the cerebellum, which then fine-tunes these movements and coordinates the muscle groups that will be involved in the movement. This happens both before and during the execution of the movement. For example, if you are grasping a jam jar, constant feedback from the cerebellum and basal ganglia to the Coretx will ensure that at the end of the movement the hand has actually reached the jam jar and not the butter dish, which is 30cm to the left.
Vestibulocerebellum
The vestibular nuclei are the intermediate stations for information coming from the organs of equilibrium (vestibular organs: macular organ and arcade organs, which are located on both sides of the inner ear). Afferences from the vestibular nuclei into the cerebellum are used for a permanent comparison of the head position with the current position of the body in space. In addition to the coordination of head movement and head posture, the cerebellum is also involved in the coordination of eye movements, which in turn must of course be coordinated with the position and movement of the head.
Information about the position of joints and muscles (so-called proprioception of propria = own and ception = perception) reaches the cerebellum from the spinal cord. Thus, the cerebellum “knows” at all times in which position the body is currently in. For example, it is possible to tell, even with closed eyes, whether and in which direction you are currently moving a single finger.
This is only possible because there are receptors in our joints, muscles and tendons that transmit information about the position of their respective seat to the CNS via the spinal cord. Here, the cerebellum has the task of adapting the holding and supporting motor activity (i.e. the body’s motor activity during standing and walking) to the respective situation. All this information reaches the cerebellum from the spinal cord, vestibular nuclei and cerebral cortex via so-called moss fibers, which end at the granule cell layer.
The granule cells are excited by these endings and in turn excite the Purkinje cells (we have already mentioned that granule cells are the only excitatory nerve cells in the cerebellum, they use the neurotransmitter glutamate). Since the Purkinje cells have an inhibitory effect, this would mean that the Purkinje cells simply massively inhibit everything they can achieve with their cell extensions. This would not be helpful for the functionality of our movement processes.
And so the other inhibiting cell types of the cerebellum come into play. Star cells, basket cells and golgi cells have an inhibitory effect on the Purkinje cells in various ways (shown in simplified form in the diagram). So what results is an inhibition of the inhibition, which means a certain, but not too strong, excitation.
To understand what exactly is excited in this way, you need to look at the upper part of the diagram. The cerebellum sends information to the spinal cord, vestibular nuclei and cerebral cortex via the Purkinje cells. This is to do exactly what was described above.
To coordinate head and body posture, to adjust eye movements to it and to direct movements in the exact direction and not to let them be chopped off but fine-tuned. The cerebellum is essentially involved in implicit learning. Well-trained movement sequences are “stored” in the cerebellum; there is no need to think while executing them. Think, for example, about riding a bicycle or car, playing the piano or dancing.