Sometimes referred to as the "little brain," the cerebellum lies on top of the pons behind the brain stem. The cerebellum is comprised of small lobes and receives information from the balance system of the inner ear, sensory nerves, and the auditory and visual systems. It is involved in the coordination of motor movements as well as basic facets of memory and learning.
The cerebellum makes up approximately 10 percent of the brain's total size, but it accounts for more than 50 percent of the total number of neurons located in the entire brain. This structure is associated with motor movement and control, but this is not because the motor commands originate here. Instead, the cerebellum serves to modify these signals and make motor movements accurate and useful.
For example, the cerebellum helps control posture, balance, and the coordination of voluntary movements. This allows different muscle groups in the body to act together and produce coordinated, fluid movement.
In addition to playing an essential role in motor control, the cerebellum is also important in certain cognitive functions including language.
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Reference: Knierim, J. (1997). Chapter 5: Cerebellum. Neuroscience Online. The University of Texas Medical School. Retrieved from http://neuroscience.uth.tmc.edu/s3/chapter05.html