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 helps us control our movements and do mental tasks such as attention and language. But its best-known job is helping us move smoothly.

The human cerebellum sits at the bottom of the brain, 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 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 an organized way. This helps the cerebellum process signals 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 has a folded layer of cortex with white matter underneath and a fluid-filled area at the base. Four deep cerebellar nuclei sit inside the white matter. Each part of the cortex has the same small group of nerve cells arranged in an organized way.

The cerebellum sits in the posterior cranial fossa. The fourth ventricle, pons and medulla are in front of it. It is separated from the cerebrum by a layer of dura mater called the cerebellar tentorium. All its connections to other parts of the brain go through the pons. The cerebellum has two sides called hemispheres and a narrow middle area called the vermis. It has many folds that split it into smaller parts. Even though the cerebellum has more nerve cells than the rest of the brain, it only takes up 10% of the brain's total space.

The surface of the cerebellum is made of a tightly folded layer of gray matter called the cerebellar cortex. Each fold in this layer is called a folium. Under the gray matter is white matter, made of nerve fibers that go to and from the cortex. Inside the white matter are four deep cerebellar nuclei, made of gray matter.

The cerebellum connects to other parts of the nervous system through three pairs of structures called cerebellar peduncles: the superior cerebellar peduncle, the middle cerebellar peduncle and the inferior cerebellar peduncle. The superior cerebellar peduncle mainly sends information out to the cerebral cortex. The middle cerebellar peduncle connects to the pons. The inferior cerebellar peduncle receives information from the vestibular nuclei, spinal cord and the tegmentum.

Function

See also: Motor coordination

The cerebellum helps us control our movements. It also helps with thinking and feelings. If the cerebellum is hurt, a person's movements can look shaky and not smooth. For example, reaching for something might look jerky.

Scientists once thought the cerebellum only helped with movement. Now we know it also helps with language, attention, and feelings. This shows the cerebellum does more than just control movement—it helps in many ways in the brain.

Clinical significance

Main article: Cerebellar ataxia

If the cerebellum is hurt, it can make moving hard. The problems you might have depend on which part of the cerebellum is affected. For example, hurt in one place might make it hard to balance and walk. Hurt in another place could make it hard to do exact moves with your hands. Doctors can find these problems by watching how a person walks and moves their fingers. They might also use special pictures to look for changes in the brain.

There are many reasons the cerebellum might get hurt, like strokes, tumors, or accidents. Some problems with the cerebellum grow slowly over time. Others might be there from when a baby is born. As people get older, the cerebellum changes too, but it seems to change more slowly than other parts of the brain.

Comparative anatomy and evolution

The cerebellum is a part of the brain. It 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

Early scientists could see the cerebellum because of its special shape. Ancient thinkers like Aristotle and Herophilus talked about it, and Galen wrote notes describing it. It was during the Renaissance that scientists studied it more closely. People like Thomas Willis and Jean Pierre Flourens found that when the cerebellum is hurt, it can make movements less smooth.

The word cerebellum means "little brain." This name comes from Latin and an even older Greek word that Aristotle used. Many names were used for this part of the brain, but cerebellum is the name we use today.