The Cerebellum

The cerebellum is part of the hindbrain, but it is not part of the brain stem. The word cerebellum means little brain. The cerebellum appears as a lobe at the back of the brain with convolutions smaller and denser than the cerebrum.

Where is the cerebellum, and what are its functions?
What happens when the cerebellum is damaged?

Among its other duties, the cerebellum serves as a storehouse for motor memories- memories of activity sequences. When the cerebellum is damaged from a birth defect or injury, the common result is loss of fine motor coordination called spasticity. The spastic gait is a distinctive way of walking in which first one foot then the other is laboriously set forward. It is a sign of cerebellar damage.

The cerebellum also participates in error-correction and problem solving of many different types, including screening out incorrect responses by other brain systems.

The cerebellum contains spectacular cells called Purkinje cells, named after a Czech physiologist. His name (POOR-kin-yay) is almost always mispronounced "per-KIN-gee" in the United States.

Packed around the Purkinje cells in the cerebellum are smaller neurons called granule cells. They are called "granule" cells because they are so tiny they appeared as little particles (granules) when first discovered. They turned out to be complete nerve cells. There are as many as 40 billion granule cells in the cerebellum. Shepherd (1974) wrote, "It is commonly stated that the human brain contains 10 billion nerve cells, as evidence of its fantastic complexity; clearly those statements do not take into account the granule cells of the cerebellum!" Humans are, as Shepherd put it, "very cerebellar animals."

How many neurons are in the brain, according to modern estimates?

Estimates of the total number of neurons in the human brain seem to increase with time. When I was in college, textbooks usually said the brain contained 10 billion nerve cells. Shepherd, in the above quote, suggests there are far more. Some scientists estimate there are one trillion (1,000,000,000,000) neurons in a human brain.

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Copyright © 2007 Russ Dewey