The cells in the blood vessel walls are joined tightly, forming the blood–brain barrier which protects the brain from toxins that might enter through the blood.Tumors of the meninges are meningiomas and are often benign. Though not technically a tumor of brain tissue, they are often considered brain tumors since they protrude into the space where the brain is, causing symptoms. Since they are usually slow-growing tumors, meningiomas can be quite large by the time symptoms appear. Brain matter
The brains of humans and other vertebrates are composed of very soft tissue and have a gelatin-like texture. Living brain tissue has a pink tint in color on the outside (gray matter), and nearly complete white on the inside (white matter), with subtle variations in color. The three largest divisions of the brain are:

Cerebral cortex
Brainstem
CerebellumThese areas are composed of two broad classes of cells: neurons and glia. These two types are equally numerous in the brain as a whole, although glial cells outnumber neurons roughly 4 to 1 in the cerebral cortex. Glia come in several types, which perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development. Primary tumors of the glial cells are called gliomas and often are malignant by the time they are diagnosed.The thalamus and hypothalamus are major divisions of the diencephalon, with the pituitary gland and pineal gland attached at the bottom; tumors of the pituitary and pineal gland are often benign.The brainstem lies between the large cerebral cortex and the spinal cord.
In aviation and underwater diving, alternobaric vertigo is dizziness resulting from unequal pressures being exerted between the ears due to one Eustachian tube being less patent than the other. Signs and symptoms
Causes
This might have occurred due to barotrauma of descent, and/or the effects of nasal decongestants. It is due to unequal increase in middle ear pressures on ascent, is usually mild, and most often cleared by further ascent. When the pressures in both ears reach ambient levels, the stimulus for the dizziness stops. Although most often mild, the vertigo can persist until the diver reaches the surface continuing the unequal pressures, which can damage the inner ear or ear drum. Alternobaric vertigo is most pronounced when the diver is in the vertical position; the spinning is towards the ear with the higher pressure and tends to develop when the pressures differ by 60 cm of water or more. Ear clearing may be a remedy. A similar vertigo can also occur as a result of unequal heating stimulation of one inner ear labyrinth over the other due to diving in a prone position in cold water - the undermost ear being stimulated. Diagnosis
In terms of diagnosis for alternobaric vertigo the medical history and physical examination, are important.