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What is the brain?

The brain is an organ that’s made up of a large mass of nerve tissue that’s protected within the skull. It plays a role in just about every major body system.

Some of its main functions include:

  • processing sensory information
  • regulating blood pressure and breathing
  • releasing hormones

Anatomy and function


The cerebrum is the largest part of the brain. It’s divided into two halves, called hemispheres. The two hemispheres are separated by a groove called the interhemispheric fissure. It’s also called the longitudinal fissure.

Each hemisphere of the cerebrum is divided into broad regions called lobes. Each lobe is associated with different functions:

  • Frontal lobes. The frontal lobes are the largest of the lobes. As indicated by their name, they’re located in the front part of the brain. They coordinates high-level behaviors, such as motor skills, problem solving, judgment, planning, and attention. The frontal lobes also manage emotions and impulse control.
  • Parietal lobes. The parietal lobes are located behind the frontal lobes. They’re involved in organizing and interpreting sensory information from other parts of the brain.
  • Temporal lobes. The temporal lobes are located on either side of the head on the same level as the ears. They coordinate specific functions, including visual memory (such as facial recognition), verbal memory (such as understanding language), and interpreting the emotions and reactions of others.
  • Occipital lobes. The occipital lobes are located in the back of the brain. They’re heavily involved in the ability to read and recognize printed words, along with other aspects of vision.


The cerebellum is located in the back of the brain, just below the occipital lobes. It’s involved with fine motor skills, which refers to the coordination of smaller, or finer, movements, especially those involving the hands and feet. It also helps the body maintain its posture, equilibrium, and balance.


The diencephalon is located at the base of the brain. It contains the:

The thalamus acts as a kind of relay station for signals coming into the brain. It’s also involved in consciousness, sleep, and memory.

The epithalamus serves as a connection between the limbic system and other parts of the brain. The limbic system is a part of the brain that’s involved with emotion, long-term memory, and behavior.

The hypothalamus helps maintain homeostasis. This refers to the balance of all bodily functions. It does this by:

  • maintaining daily physiological cycles, such as the sleep-wake cycle
  • controlling appetite
  • regulating body temperature
  • controlling the producing and release of hormones

Brain stem

The brain stem is located in front of the cerebellum and connects to the spinal cord. It consists of three major parts:

  • Midbrain. The midbrain helps control eye movement and processes visual and auditory information.
  • Pons. This is the largest part of the brain stem. It’s located below the midbrain. It’s a group of nerves that help connect different parts of the brain. The pons also contains the start of some of the cranial nerves. These nerves are involved in facial movements and transmitting sensory information.
  • Medulla oblongata. The medulla oblongata is the lowest part of the brain. It acts as the control center for the function of the heart and lungs. It helps regulate many important functions, including breathing, sneezing, and swallowing.

Brain diagram

Use this interactive 3-D diagram to explore the brain.

Brain conditions

There are hundreds of conditions that can affect the brain. Most of them fall within one of five main categories:

Learn more about the different types of brain conditions.

Symptoms of a brain condition

The brain is one of your most important body parts, so it’s important to know how to recognize signs that there may be a problem.

Brain injury symptoms

Brain injury symptoms depend on the type and severity of the injury. While they sometimes appear immediately after a traumatic event, they can also show up hours or days later.

General brain injury symptoms may include:

  • headache
  • nausea or vomiting
  • feeling confused or disoriented
  • dizziness
  • feeling tired or drowsy
  • speech problems, including slurring
  • sleeping more or less than usual
  • dilation of one or both pupils
  • fluid draining from your nose or ears
  • seizures
  • sensory problems, such as blurry vision or a ringing in your ears
  • trouble remembering things or difficulty concentrating
  • mood swings or unusual behavior

Cerebrovascular injury symptoms

Symptoms tend to come on suddenly and include:

  • severe headache
  • loss of vision
  • inability to speak
  • inability to move or feel a part of the body
  • drooping face
  • coma

Brain tumor symptoms

Brain tumor symptoms depend on the size, location, and type of tumor.

General brain tumor symptoms may include:

  • headache
  • nausea or vomiting
  • loss of motor coordination, such as trouble walking
  • feeling sleepy
  • feelings of weakness
  • appetite changes
  • convulsions or seizures
  • issues with your vision, hearing, or speech
  • difficulty concentrating
  • mood swings or behavior changes

Neurodegenerative symptoms

Neurodegenerative diseases cause damage to nervous tissue over time, so their symptoms may get worse as time goes on.

General neurodegenerative symptoms include:

  • memory loss or forgetfulness
  • changes in mood, personality, or behavior
  • issues with motor coordination, such as difficulty walking or staying balanced
  • speech issues, such as slurring or hesitation before speaking

Psychological symptoms

Symptoms of psychological conditions can be very different from person to person, even when they involve the same condition.

Some general symptoms of a psychological condition include:

  • excessive feelings of fear, worry, or guilt
  • feeling sad or dejected
  • confusion
  • difficulty concentrating
  • low energy
  • extreme stress that gets in the way of daily activities
  • extreme mood swings
  • withdrawal from loved ones or activities
  • delusions or hallucinations
  • suicidal ideation

Tips for a healthy brain

Follow these tips to keep your brain in good health and to reduce your risk of certain brain conditions:

Use it or lose it

Improve your mental fitness by regularly reading, learning, or doing activities that make you think, such as crossword puzzles. All of these help stimulate your nerve cells, and may even lead to the development of new brain cells.

Protect your head

Always wear a helmet when playing contact sports. Be sure to buckle up when you get in the car. Both of these can go a long way when it comes to avoiding brain injuries.


Doing regular cardio workouts stimulates blood flow throughout your body, including your brain.

Quit smoking

While smoking is bad for your overall health, it can also lead to cognitive decline.

Listen to your thoughts

Try to check in from time to time with your thoughts or feelings. Keeping a diary is a good way to get into this habit. Look for any thought patterns or emotions that seem to be impacting your day-to-day life. They could be a sign of an underlying, treatable psychological condition.