What is the cerebellum?
The cerebellum is a distinct brain structure in the lower, back
portion of the brain. Despite all the ways the brain has changed
through mammalian evolution, the cerebellum is one structure that has
remained relatively the same. This means that your cerebellum isn’t
that different from your dog’s cerebellum.
The cerebellum controls movement, balance, and posture. Within the
large realm of movement, the cerebellum’s special role is to help you
learn new movements. For example, if you try to learn a new jump in
a ballet class, your cerebellum will help you fine–tune your movement
until you get it right. Most neuroscientists agree that the cerebellum
fine–tunes movement by sending an error message when your executed
movement is inconsistent with your planned movement.
Although the cerebellum is small compared to the rest of the human
brain, the cerebellum contains more than 50% of all the neurons in
the brain. The main cells in the cerebellum are called Purkinje cells.
Purkinje cells are neurons that have exquisitely complex dendrites that
look like tree branches. Purkinje cells receive excitatory signals from
two types of neurons: granule cells and climbing fibers. Each Purkinje
cell receives large error messages that help fix incorrect movements
from just one climbing fiber. In contrast, each Purkinje cell receives
input from thousands of granule cells. Granule cells are the most
numerous neurons in the cerebellum and in the entire brain, and they
look like lentils under a microscope. All together, a properly
functioning cerebellar circuit with Purkinje cells, granule cells, and
climbing fibers, will keep you evenly balanced on your toes.