The structure of the cerebellum

The term cerebellum is from the Latin meaning "the little brain". If we look beneath the back of the large wrinkled surface of what we typically think of as the brain (the cerebral cortex), we see a smaller, even more tightly wrinkled portion: the cerebellum.

The cerebellum (shaded pink) sits beneath the back of the cerebral cortex.

Inside, the cerebellum is divided into distinct layers.
If we look inside the cerebellum, we see that it is divided into distinct layers. The innermost layer consists of white matter (W). These are the nerve fibers carrying information in and out of the cerebellum. You can think of the white matter like the phone lines carrying calls in and out of a switchboard. The outermost layer of the cerebellum is called the molecular layer. This is where the fibers from different nerve cells communicate with each other. In between is the layer packed with small, purple nerve cells, the granule cell layer. These cells function like the computer that will decide what to do with all the information coming in.

The Purkinje cells are critical for normal function of the cerebellum
Lined up at the border between the two outer layers of the cerebellum is a single row of very large cells, the Purkinje cells, named after the famous neuroanatomist who first described them. These are the cells that communicate the decision about how to best fine-tune the movements back to the rest of the brain and the muscles. Without the Purkinje cells, all the work of the cerebellum is for naught because the results do not get communicated to where that information is needed.
Since balance is an important part of movement, the cerebellum works very closely with the part of the brain that controls balance, the vestibular system. Deep within the skull benath the eardrum, there are a series of fluid filled spaces. Some of these spaces are circular canals. When an animal moves its head, the fluid in these canals flows and sensors use that information to detect movement of the head. Other spaces contain tiny granules. The pressure from those granules on sensors allows the dog to sense the pull of gravity.
Information from the inner ear about movement & pull of gravity is shared with the cerebellum to control balance