Cerebellum

The cerebellum (pl.: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Though usually smaller than the cerebrum, in some animals like the mormyrid fishes, it can be just as large or even larger. In humans, the cerebellum is very important for controlling movements and for mental tasks such as attention and language, as well as managing emotions like fear and pleasure. However, its best-known job is helping us move smoothly.

The human cerebellum sits at the bottom of the brain, tucked under the cerebral hemispheres. It looks like a separate part, with a surface covered in tiny parallel grooves, unlike the big folds of the cerebral cortex. These grooves show that the cerebellar surface is actually a thin layer of tissue folded like an accordion. Inside this layer are special types of neurons, especially Purkinje cells and granule cells, arranged in a very organized way. This setup lets the cerebellum process signals very well, and most of its messages pass through small groups of cells called deep nuclei inside its white matter.

Besides controlling movement, the cerebellum also helps us learn new motor skills, like adjusting to changes in how our body moves. Scientists have created theories, such as the Marr–Albus theory, to explain how the cerebellum learns these skills. These theories suggest that special signals help change the strength of connections between cells, allowing us to improve our movements over time.

Structure

Main article: Anatomy of the cerebellum

The cerebellum is part of the hindbrain in all vertebrates. It consists of a folded layer of cortex with white matter underneath and a fluid-filled ventricle at the base. Four deep cerebellar nuclei are embedded in the white matter. Each part of the cortex has the same small set of nerve cells arranged in a very organized way.

The cerebellum is located in the posterior cranial fossa. The fourth ventricle, pons and medulla are in front of it. It is separated from the overlying cerebrum by a layer of dura mater, the cerebellar tentorium; all of its connections with other parts of the brain travel through the pons. The cerebellum is divided into two cerebellar hemispheres; it also contains a narrow midline zone (the vermis). It has large folds that divide it into 10 smaller lobules. Because of its many tiny granule cells, the cerebellum contains more neurons than the rest of the brain, but takes up only 10% of the total brain volume.

The surface of the cerebellum is made up of a tightly folded layer of gray matter: the cerebellar cortex. Each ridge or gyrus in this layer is called a folium. Underneath the gray matter of the cortex lies white matter, made up largely of nerve fibers running to and from the cortex. Embedded within the white matter are four deep cerebellar nuclei, composed of gray matter.

Connecting the cerebellum to different parts of the nervous system are three paired cerebellar peduncles: the superior cerebellar peduncle, the middle cerebellar peduncle and the inferior cerebellar peduncle. The superior cerebellar peduncle is mainly an output to the cerebral cortex. The middle cerebellar peduncle is connected to the pons. The inferior cerebellar peduncle receives input from the vestibular nuclei, spinal cord and the tegmentum.

Function

See also: Motor coordination

The cerebellum helps control our movements and also plays a role in thinking and emotions. When the cerebellum is damaged, a person’s movements become shaky and uncoordinated. For example, reaching for an object might look jerky instead of smooth.

Scientists used to think the cerebellum only helped with movement. Now we know it also helps with things like language, attention, and feelings. This shows the cerebellum is more than just a movement controller—it’s involved in many brain functions.

Clinical significance

Main article: Cerebellar ataxia

When the cerebellum is damaged, it can cause problems with movement. The specific issues depend on which part of the cerebellum is affected. For example, damage to one area might make it hard to balance and walk, while damage to another area could make it difficult to make precise hand movements. Doctors can test for cerebellar problems by watching how a person walks and moves their fingers, and they might use special imaging to see if there are any changes in the brain.

There are many reasons the cerebellum might be damaged, such as strokes, tumors, or injuries. Some conditions that affect the cerebellum develop over time, and others can be present from birth. As people age, the cerebellum changes, but it seems to age more slowly than other parts of the brain.

Comparative anatomy and evolution

The cerebellum, a part of the brain, has similar circuits in all vertebrates, including fish, reptiles, birds, and mammals. It is also found in clever animals like octopuses. The size and shape of the cerebellum change across different animals. It is small in amphibians and barely noticeable in lampreys and hagfish. It grows larger in reptiles, even more in birds, and is quite large in mammals. In some fish, especially mormyrid fish, the cerebellum can be as large as or even larger than the rest of the brain.

In mammals, the cerebellum has expanded lateral lobes that work with the neocortex. As monkeys evolved into apes, these lobes grew along with the brain's frontal lobes. In human evolution, the cerebellum continued to grow, possibly contributing to better cognitive abilities. The cerebellum's growth in humans may be linked to improved motor skills and learning. Today, the lateral hemispheres of the human cerebellum are much larger than those in monkeys.

History

Even the earliest scientists could recognize the cerebellum because of its unique shape. Ancient thinkers like Aristotle and Herophilus described it, and Galen wrote detailed notes about it. It wasn’t until later, during the Renaissance, that more thorough studies began. Scientists like Thomas Willis and Jean Pierre Flourens discovered that damage to the cerebellum affects movement, making motions less smooth and coordinated.

The word cerebellum means "little brain," a term that comes from Latin and translates an even older Greek word used by Aristotle. Over time, many different names were used for this part of the brain, but cerebellum is the one we use today.