The cerebellum is one of the smaller parts of the brain but has a role to play in many different mental and physical processes. This part of the brain is chiefly responsible for managing, but not directly initiating, certain types of movement. The ability to balance and facility in maintaining posture are both among the most important functions of the cerebellum. Parts of it are also responsible for or tangentially involved in a wide variety of other neural processes. These include learning and related cognitive functions as well as focus and response to some environmental stimuli.
Structurally, the cerebellum resembles a secondary brain mounted at the base of the brain. One widely-accepted way of thinking about the cerebellum envisions it as a sort of parallel processing device that handles certain key tasks, but in a relatively linear and subordinate fashion. This part of the brain is made up of many segments of nerves that all share a basic configuration. Each segment accepts a wide variety of input, processes that input in a thorough and complicated fashion, and then passes on a relatively simple output. This type of computation and processing facilitates the semi-autonomous handling of many routine but crucial tasks.
One of the functions of the cerebellum that falls into this category has to do with balance. The human body must constantly make many small adjustments in order to remain upright. These are largely handled by a portion of the cerebellum, which processes balance without the need for active thought.
Moving a human body efficiently and safely is also a very complicated task. Another of the functions of the cerebellum is to aid in the process of movement. The cerebellum does not begin movements but serves as a sort of assistant to make movement happen more smoothly when it is initiated by other portions of the brain.
The process of movement involves constant attention to the current position of the body and its direction of movement. A healthy cerebellum allows for smooth and straight muscular movements. A damaged one produces awkward and jerky motions as the higher brain tries to direct movement, a task for which it is ill-suited.
Other functions of the cerebellum tend to make use of its ability to sort and process certain types of information and then send output to areas of the brain or nervous system where that information is useful. The cerebellum is involved in several types of learning and seems to be especially important in learning that requires small adjustments to patterns of motion. Additional functions of the cerebellum are the transmission of data to areas such as the digestive system or the eyes in response to environmental stimuli or other neural responses.