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At the rear of the brain is the cerebellum. The cerebellum is similar to the cerebrum in that each has hemispheres that control the opposite side of the body and are covered by gray matter and surface folds. The vermis, which is a central constricted area, connects the hemispheres.

The cerebellum is concerned with the automatic regulation of movement and posture, and the learning of new motor patterns. The cerebellum basically coordinates body movement and is located at the back of the brain beneath the occipital lobes.

The cerebellum fine tunes motor activity or movement such as the fine movements of fingers. The cerebellum controls balance or equilibrium, posture, and coordination by controlling the tone of muscles and the position of limbs. The cerebellum is important in one's ability to perform rapid and repetitive actions such as playing a video game. In the cerebellum, right-sided abnormalities produce symptoms on the same side of the body.

The cerebellum functions closely with the cerebral cortex and the brain stem. It's separated from the cerebrum by the fold of dura called the tentorium. It's divided into two lateral lobes connected by a fingerlike bundle of white fibers called vermis. The outer layer of the cerebellum consists of fine folds called folia. Three fiber bundles called cerebellar peduncles connect the cerebellum to the three parts of the brain stem: The midbrain, the pons, and the medulla oblongata.

Damage to the cerebellum or the cerebellar peduncles is very common in multiple sclerosis (MS) due to the large amount of white matter in these structures.

Some of symptoms associated with damage to the cerebellum or the nervous tracts leading to it are:
Dysdiadokokinesia (difficulty in performing rapid alternating movements)
Ataxia (difficulty in coordinating movements)
Loss of balance and vertigo
Muscle weakness
Dysarthria (loss of coordination of the muscles controlling speech)
Loss of postural tone
White Matter
The white matter regions of the central nervous system (CNS) contrast with the gray matter regions. The white matter refers to those parts of the brain and spinal cord that are responsible for communication between the various gray matter regions and between the gray matter and the rest of the body. In essence, the gray matter is where the processing is done and the white matter is the channels of communication.

The white matter is so-called because it contains many nerve fibers or neurons that are sheathed in the white fatty insulating protein called myelin. In section, myelin is white whereas the gray matter is that color due to all the gray nuclei contained in the cells that make it up.

The white matter is found in the inner layer of the cortex, the optic nerves, the central and lower areas of the brain or brainstem, and surrounding the central shaft of gray matter in the spinal cord.

MS is predominantly a disease of the white matter in the CNS. About 95% of all lesions associated with MS occur in the white matter.
Gray Matter
The gray matter regions of the CNS, the brain and spinal cord, contrast with the white matter regions. The gray matter is the areas where the actual "processing" is done whereas the white matter provides the communication between different gray matter areas and between the gray matter and the rest of the body.

The neurons in the gray matter consist of neuronal cell bodies and their dendrites. The dendrites are short protrusions that communicate with immediately neighboring neurons in the CNS. In contrast with the neurons of the white matter, gray matter neurons don't contain long axons that transmit the nerve impulses to more distant regions of the CNS.

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About 40% of the human brain is made up of gray matter and the other 60% is white matter. The gray matter, however, consumes about 94% of the total oxygen used by the brain.

The vast majority of MS lesions occur in the white matter areas but a small number, about 5%, do occur within the gray matter. Gray matter is so-called because in section it has a gray color due to all the gray nuclei in the cells that make it up.

Gray matter involvement is detected even in the earliest stages of MS, and gray matter atrophy occurs at a faster rate than white matter atrophy early in the disease course.

Studies have determined that:
Gray matter involvement and in particular cortical demyelination can be extensive in MS.
Gray matter pathology may occur in part independently of white matter lesion formation.
A primarily gray matter-related process may be the earliest manifestation of MS.
Gray matter involvement is associated with physical disability, fatigue, and cognitive impairment in MS.
Gray matter disease might help explain the observed dissociation between markers of inflammatory demyelination (relapses, white matter gadolinium enhancement, white matter lesion burden) and disease progression.

It's likely that gray matter damage is related to white matter damage. However, continued studies of gray matter pathology as well as neuronal and axonal involvement in MS and related experimental models are necessary to better understand the etiology and pathogenesis of the degenerative components.

In a recent supplement to Neurology, it was stated basically that recent studies have found that gray matter damage, which isn't effectively detected through MRI, may be more pronounced than white matter damage, especially early in the disease process, and can have considerable impact on clinico-cognitive functioning and neuro-psychological deficits. So gray matter damage is probably greater than earlier believed or seen on an MRI and because of this finding, it's felt that cognitive and psychological functions may have been impacted to a greater extent.