Healthy people possess levels of brain chemicals that lie within a certain normal range. When internal or external factors either deplete the brain of these chemicals or stimulate it to produce excess amounts, a chemical imbalance occurs.

Brain swelling, known in medical terminology as cerebral edema, is a manifestation of various brain injuries such as cancer or trauma, and is dangerous because it raises the pressure inside the skull. The skull is a thick chamber that is not compliant, which means it does not stretch.

Sudden short-term memory loss is often as frightening for loved ones as it is for the sufferer. The fact that it comes on suddenly yields clues to its possible causes. New cases of confusion or sudden memory loss for no apparent reason should be evaluated by a medical professional immediately.

Memory lapses happen to everyone at times. Your teen may forget where he placed homework or what time you told him to go to his doctor's appointment. These lapses are normal glitches that occur within his brain because it's busy sorting, storing and recalling other details.

The cerebellum is located in the posterior fossa along with the fourth ventricle and brain stem. Approximately 15 to 20 percent of tumors arise in the posterior fossa, according to New York Presbyterian Hospital.

Dopamine and dobutamine are both substances that have important actions on our bodies. Both act at specific cell receptors and produce significant changes in those cells. Dobutamine is a drug that acts on the sympathetic nervous system. Physicians use it to treat heart failure and cardiogenic shock.

Alpha when we are in a state of physical and mental relaxation, although aware of what is happening around us, its frequency are around 7 to 13 pulses per second.

A brain aneurysm is a bulge or dilation in an artery in the brain. Aneurysms occur in areas where the walls of the artery are thin or weak. Aneurysms develop in approximately one in 20 people, according to the Merck Manual.

Gabapentin is an anticonvulsant medication used in the treatment of epileptic seizures. Gabapentin is also used to relieve the pain of postherpetic neuralgia (PHN; the burning, stabbing pain or aches that may last for months or years after an attack of shingles), reports Medline Plus.

Brain tumors that begin in the brain are called primary brain tumors, and they may or may not be cancerous. Other brain tumors arise when cancer from another location in the body spreads, or metastasizes, to the brain. These metastatic brain tumors are 4 to 5 times more common than primary brain tumors.

Concussions are one of the most common types of minor head injuries. Each year, 300,000 Americans suffer concussions related to sports and recreation activities, according to the Franklin Institute.

No matter how vigilant you are, accidents happen, and babies sometimes sustain bumps on the head. When these incidents occur, worry about a possible concussion or more serious brain injury often follows. A concussion refers to a mild brain injury that temporarily disrupts normal brain function.