the cerebral white matter. The cerebellum is structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white matter (called the "arbor vitae") and aggregates of grey matter surrounded by deep cerebellar white matter (dentate nucleus, globose nucleus, emboliform nucleus, and fastigial nucleus). The fluid-filled cerebral ventricles (lateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle) are also located deep within the cerebral white matter. Myelinated axon length Men have more white matter than women both in volume and in length of myelinated axons. At the age of 20, the total length of myelinated fibers in men is 176,000 km while that of a woman is 149,000 km. There is a decline in total length with age of about 10% each decade such that a man at 80 years of age has 97,200 km and a female 82,000 km. Most of this reduction is due to the loss of thinner fibers. However, this study only included 36 participants. Function White matter is the tissue through which messages pass between different areas of grey matter within the central nervous system. The white matter is white because of the fatty substance (myelin) that surrounds the nerve fibers (axons). This myelin is found in almost all long nerve fibers, and acts as an electrical insulation. This is important because it allows the messages to pass quickly from place to place. Unlike grey matter, which peaks in development in a person's twenties, the white matter continues to develop, and peaks in middle age. Research Multiple sclerosis (MS) is the most common of the inflammatory demyelinating diseases of the central nervous system which affect white matter. In MS lesions, the myelin sheath around the axons is deteriorated by inflammation. Alcohol use disorders are associated with a decrease in white matter volume. Amyloid plaques in white matter may be associated with Alzheimer's disease and other neurodegenerative diseases. Other changes that commonly occur with age include the development of leukoaraiosis, which is a rarefaction of the white matter that can be correlated with a variety of conditions, including loss of myelin pallor, axonal loss, and diminished restrictive function of the blood–brain barrier. There is also evidence that substance abuse may damage white matter microstucture, though prolonged abstinence may in certain cases may reverse such white matter changes. White matter lesions on magnetic resonance imaging are linked to several adverse outcomes, such