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Diseases & Conditions A - Z
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Brain Health Overview

The brain is the most important part of the body. It controls almost all body processes, including heartbeat, breathing, digestion, muscle movement, and speech, as well as all five senses. The brain is also responsible for memory, emotion, and reasoning.

Brain Structure

The brain is an extremely complex structure, but it can be summarized by four main parts:

Brain Stem

The brain stem is at the bottom of the brain, attached directly to the spinal cord. It controls the many involuntary, but necessary, processes that take place in the body, including breathing, pulse, and blood pressure. Many of the cranial nerves that control facial movements, swallowing, the tongue, shoulder shrugging, and heart rate emerge from the brain stem.


The cerebellum is behind and on top of the brain stem. It is responsible for movement and balance. Many of the higher brain functions that emerge from the cerebrum pass through the cerebellum before being executed by the body.

Limbic System

The limbic system is a collection of several structures at the center of the brain that controls emotion and memory.


The cerebrum is the largest part of the brain and sits atop the others. It is divided into left and right halves, called hemispheres. The left hemisphere controls the right side of the body, and the right hemisphere controls the left side of the body. Each hemisphere is subdivided into four lobes:

  • frontal lobes are responsible for logical reasoning and problem solving
  • parietal lobes for spatial orientation, integrating sensory information, and motor function
  • occipital lobes for vision
  • temporal lobes for hearing and speech

When Things Go Wrong

One unfortunate consequence of the brain's complexity and responsibility for so many functions is that many different things can go wrong with it, which can cause symptoms all over the body.

Brain Trauma

Brain trauma happens suddenly and usually requires immediate treatment.


A concussion is a sharp blow to the head that causes the brain to collide against the inside of the skull. Symptoms usually last for a few days and up to two week and can include:

  • drowsiness
  • severe headache
  • confusion
  • memory loss
  • nausea

Anyone who suffers a blow to the head needs to seek medical attention. This is especially true if the person loses consciousness at any time. It is not uncommon to suffer a sharp blow to the head, lose consciousness, and then wake up and feel fine. However, there could be bleeding in the brain that, if not detected by imaging of the brain, may be fatal.


A brain aneurysm is a bulge in an artery in the brain. Common symptoms include:

  • pain behind the eyes
  • numbness or weakness in the face
  • double or blurry vision

If untreated, an aneurysm can rupture and cause a sudden, extremely severe headache. A ruptured aneurysm can be deadly if not treated quickly.


A stroke is an interruption of blood flow to part of the brain caused by bleeding in the brain or by a blood clot clogging an artery. Stroke symptoms come on suddenly and may include:

  • confusion
  • trouble speaking
  • dizziness
  • headache
  • numbness or weakness on one side of the body

If you experience symptoms of a stroke, it is essential to seek medical attention as soon as possible. When a stroke occurs, time is critical. Prompt treatment can save areas of brain from permanent damage.

Degenerative Brain Diseases

Degenerative brain diseases cause progressive damage to the parts of the brain that control cognition and emotion. The damage tends to accumulate and increase over a long period of time.


The most common form of degenerative brain disease is dementia. People with dementia undergo a gradual loss of intellectual and cognitive abilities over time. The initial signs and symptoms of dementia may be subtle at first but may progress from lapses in memory to include:

  • trouble dealing with numbers and directions
  • difficulty speaking and understanding language
  • personality changes
  • an inability to perform even basic tasks

Dementia can rob an individual of their independence and personality. This disease is very difficult for the patients as well as their caregivers.

Alzheimer’s disease is the most common form of dementia, accounting for 50 to 70 percent of all dementia cases. Other types of dementia include vascular dementia, Lewy body dementia, and fronto-temporal dementia. There is also a type of dementia associated with Parkinson’s disease, though this is much rarer than other types of dementia. The onset of dementia is most common in people who are in their 70s and 80s and is rare before age 40. Both the incidence (the number of new cases per year in the population) and the prevalence (the fraction of the population that has the disorder) rise steeply with age.

Alzheimer’s Disease

Although Alzheimer’s disease is the most common type of dementia, the precise cause of Alzheimer's disease is still unknown. However, there is convincing evidence that the slow, irreversible destruction of brain cells is caused when abnormal proteins collect in the brain. Like all forms of dementia, Alzheimer’s most common among older people; symptoms are rarely seen in people under 60. Medicines for Alzheimer’s disease act to increase the amount of brain chemicals called neurotransmitters. These medicines may be marginally useful in mild to moderate Alzheimer’s but show no benefit in advanced cases of Alzheimer’s disease.

Other Causes of Dementia

Other causes of dementia include strokes, Parkinson’s disease, Huntington’s disease, multiple sclerosis, and imbalances in micronutrients. While each of these diseases has unique pathology, prognosis, and treatments, the ‘end game’ for all can be dementia. If you are concerned that a member of your family is beginning to show signs of dementia, it is important that the individual be evaluated by a physician. Several basic tests can help your physician determine whether any of the symptoms are reversible and how to support the patient as they begin to deal with any new diagnosis.


Epilepsy is a disease that causes abnormal electrical discharges in the brain. The main symptom of epilepsy is repeated seizures, which are episodes of disturbed brain function. A seizure can manifest as one or more of the following symptoms:

  • temporarily altered perception of sounds, smells, sights, and tastes
  • uncontrollable jerking of the muscles
  • staring or repeated motions
  • complete loss of consciousness

Depending on the type of seizure, individuals may lose bladder and bowel function during a seizure.

Having one seizure alone does not mean a person has epilepsy; epilepsy is only diagnosed when an individual has had more than one seizure without an underlying cause like a fever or toxin. 

Content licensed from:

Written by: the Healthline Editorial Team
Published on: Sep 21, 2010
Medically reviewed : Jennifer Monti, MD, MPH

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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