Cerebellum

http://www.brainfacts.org/brain-basics/neuroanatomy/articles/2012/the-cerebellum/

The cerebellum stores learned sequences of movements, it participates in fine tuning and co-ordination of movements produced elsewhere in the brain, and it integrates all of these things to produce movements so fluid and harmonious that we are not even aware of them.

The pathologies of the cerebellum have long revealed that this part of the brain is involved in motor co-ordination. The cerebellum is divided into three regions, each of which is connected to a specific structure in the brain and involved in a specific function.

• The archicerebellum (or vestibulocerebellum) first appeared in fish. It is connected to the vestibule of the inner ear and is involved in balance.
• The palaeocerebellum is connected to the spinal cord and controls postural muscle activity by influencing muscle tonus. To play its role in maintaining body posture, a muscle must be tensed. The cerebellum therefore controls muscle tension at all times while releasing those muscles required to execute movements.
• In mammals, the neocerebellum is connected to the cortex and contributes to the co-ordination of voluntary movements. Among other functions, it ensures that when one set of muscles initiates a movement, the opposing set acts as a brake so that the body part in question arrives at its target precisely.

For the body to make any given gesture, the sequence and duration of each of the basic movements of each body segment involved must be controlled in a very precise manner. One of the cerebellum's jobs is to provide this control over the timing of the body's movements. It does so by means of a loop circuit that connects it to the motor cortex and modulates the signals that the motor cortex sends to the motor neurons. 

In humans, the cerebellum also plays a role in analyzing the visual signals associated with movement. These signals may come either from the movement of objects within the field of vision or from the sight of the moving body segments themselves. The cerebellum appears to calculate the speed of these movements and adjust the motor commands accordingly. Errors in such calculations largely account for the poor motor control observed in patients who have suffered injuries to the cerebellum.

As regards cognitive impairments, some signs of cerebellar involvement have been found in the areas of language, attention, memory, and emotions. For example, in some autistic children, cognitive delays have been partly attributed to insufficient development of certain parts of the cerebellum. 

Lastly, another important property of the cerebellum is its ability to learn and remember, which is based, among other things, on the distinctive cell architecture of the cerebellar cortex.

Cerebellar syndrome is the term used to designate manifestations of damage to the cerebellum, regardless of origin. For example, if a patient with cerebellar syndrome tries to touch an object, the movement of his hand will begin late, then accelerate beyond what is normal. Braking also will be too late, and inefficient, so that his hand ends up missing the object and going past it. This movement then ends with oscillations of the hand and arm.

People with cerebellar syndrome also appear to have some problems in co-ordinating balance and posture. These people have an uncertain gait, spreading their feet more widely apart as they strike the ground. If these people are jostled, the reflexes that compensate for the imbalance overreact, often resulting in oscillations of the entire body. These people also cannot tilt their trunks forward or backward without losing their balance.

Cerebellum A large structure located at the roof of in the hindbrain that helps control the coordination of movement by making connections to the pons, medulla, spinal cord, and thalamus.

Another part of the hindbrain is the cerebellum which, like the cerebrum, also has two hemispheres. The cerebellum’s two hemispheres help control movement and cognitive processes that require precise timing, and also play an important role in Pavlovian learning

Nondeclarative knowledge, the knowledge of how to do something, often called procedural memory, is expressed in skilled behavior and learned habits and requires processing by the basal ganglia and cerebellum. The cerebellum is specifically involved in motor tasks that involve coordinated timing. The amygdala appears to play an important role in the emotional aspects of memory, attaching emotional significance to otherwise neutral stimuli and events.

 movement control involves the interaction of the cerebellum

The cerebellum is crucial for coordinating and adjusting skilled movement. A disturbance of cerebellar function leads to poor coordination of muscle control, disorders of balance and reaching, and even difficulties in speech, one of the most intricate forms of movement control

 The cerebellum apparently acts to integrate all this information to ensure smooth coordination of muscle action, enabling us to perform skilled movements more or less automatically. The cerebellum also helps us adjust motor output to deal with changing conditions, such as growth, disability, changes in weight, and aging. It tunes motor output to be appropriate to the specific requirements of each new task. Evidence suggests that as we learn different processes detailed control information is stored within the cerebellum, where it can be called upon by commands from the cerebral cortex.