Brain

Overview

What is the brain?

Your brain is an essential organ. All of your emotions, sensations, aspirations and everything that makes you uniquely individual come from your brain. This complex organ has many functions. It receives, processes and interprets information. Your brain also stores memories and controls your movements.

Your brain is one component of your central nervous system (CNS). It connects to your spinal cord, the other part of your CNS.

Function

What is the brain’s function?

Your brain receives information from your five senses: sight, smell, sound, touch and taste. Your brain also receives inputs including touch, vibration, pain and temperature from the rest of your body as well as autonomic (involuntary) inputs from your organs. It interprets this information so you can understand and associate meaning with what goes on around you.

Your brain enables:

  • Thoughts and decisions.
  • Memories and emotions.
  • Movements (motor function), balance and coordination.
  • Perception of various sensations including pain.
  • Automatic behavior such as breathing, heart rate, sleep and temperature control.
  • Regulation of organ function.
  • Speech and language functions.
  • Fight or flight response (stress response).

Anatomy

What are the main parts of the brain?

Your brain’s structure is complex. It has three main sections:

  • Cerebrum: Your cerebrum interprets sights, sounds and touches. It also regulates emotions, reasoning and learning. Your cerebrum makes up about 80% of your brain.
  • Cerebellum: Your cerebellum maintains your balance, posture, coordination and fine motor skills. It's located in the back of your brain.
  • Brainstem: Your brainstem regulates many automatic body functions. You don’t consciously control these functions, like your heart rate, breathing, sleep and wake cycles, and swallowing. Your brainstem is in the lower part of your brain. It connects the rest of your brain to your spinal cord.

What are the lobes that make up your brain?

Each side of your brain has different lobes (sections). While all the lobes work together to ensure normal functioning, each lobe plays an important role in some specific brain and body functions:

  • Frontal lobes: The frontal lobes are in the front part of your brain, right behind your forehead. This is the largest lobe and it controls voluntary movement, speech and intellect. The parts of your frontal lobes that control movement are called the primary motor cortex or precentral gyrus. The parts of your brain that play an important role in memory, intelligence and personality include your prefrontal cortex as well as many other regions of your brain.
  • Occipital lobes: These lobes in the back of your brain allow you to notice and interpret visual information. Your occipital lobes control how you process shapes, colors and movement.
  • Parietal lobes: The parietal lobes are near the center of your brain. They receive and interpret signals from other parts of your brain. This part of your brain integrates many sensory inputs so that you can understand your environment and the state of your body. This part of your brain helps give meaning to what's going on in your environment.
  • Temporal lobes: These parts of the brain are near your ears on each side of your brain. The temporal lobes are important in being able to recall words or places that you've been. It also helps you recognize people, understand language and interpret other people’s emotions.
  • Limbic lobes: The limbic lobe sits deep in the middle portions of your brain. The limbic lobe is a part of your temporal, parietal and frontal lobes. Important parts of your limbic system include your amygdala (best known for regulating your “fight or flight” response) and your hippocampus (where you store short-term memories).
  • Insular lobes: The insular lobes sit deep in the temporal, parietal and frontal lobes. The insular lobe is involved in the processing of many sensory inputs including sensory and motor inputs, autonomic inputs, pain perception, perceiving what is heard and overall body perception (the perception of your environment).

What is the difference between the left and right brain hemispheres?

Your cerebrum divides into two halves: the left and right cerebral hemispheres. The two halves of the brain are connected by nerve fiber bundles (white matter) called your corpus callosum. The right side of your cerebrum controls movement on the left side of your body and vice versa.

Your left brain hemisphere is often the “dominant” hemisphere — but this doesn’t apply to everyone. Most people who are right-handed are usually left hemisphere dominant. Some patients who are left-handed are right hemisphere is dominant. Typically, the dominant hemisphere is responsible for your speech and language functions. Your non-dominant (which is the right hemisphere in most individuals) is responsible for your spatial awareness and processing of what you see.

About 1 in 10 right-handed people and about 1 in 3 left-handed people have dominance in the right hemisphere. This means that their speech functions are mostly centered in the right side of their brains. Many times this is a normal variant but in some people with brain tumors or epilepsy, the dominance can be shifted through a process called brain plasticity.

What are the bones and tissues that protect your brain?

A bony structure called your cranium surrounds your brain. Your cranium is part of your skull. All the bones of your skull protect your brain from injury.

Between your brain and skull, you have three layers of tissue called the meninges:

  • Dura mater: The outermost layer lines your entire skull. Parts of the dura mater form folds that separate the right half of your brain from the left.
  • Arachnoid: The middle layer of the meninges is a thin, fragile layer of tissue that covers your entire brain.
  • Pia mater: The innermost layer contains blood vessels that run into your brain’s surface.

Between your arachnoid and pia mater tissue is a clear substance called your cerebrospinal fluid (CSF). CSF also surrounds your spinal cord, which runs through the vertebrae (bones of your spine). CSF cushions and protects these vital nervous system organs.

What is the gray and white matter in the brain?

Substances called gray and white matter make up your central nervous system. In your brain, gray matter is the outermost layer. It plays a significant part in your day-to-day function.

White matter is your deeper brain tissue. It contains nerve fibers that help your brain send electric nerve signals more quickly and efficiently.

Which nerves send signals to and from your brain?

Your brain contains several types of nerves. Nerves carry messages by sending electrical impulses back and forth between your brain, organs and muscles. The nerves in your brain are called cranial nerves. You have 12 pairs of cranial nerves from the brain to parts of your head and face. These nerves are responsible for specific sensations, such as hearing, taste or sight. White matter is the fiber bundles that connect brain cells. There are numerous white matter tracts that connect one area of your brain to another, as well as structures deep in your brain. These white matter tracts can also travel to your brainstem and spinal cord so that information can be relayed from your brain to communicate with the rest of your body and information from your body can travel to your brain.

What other parts of the brain send and receive signals?

Although most brain cells reside on the surface of your brain (called gray matter) and the cabling (white matter) is deep and connects various parts of your brain, there are some nuclei (collection of brain cells) that reside deep in your brain. They include:

  • Thalamus: Your thalamus is a structure residing deep in your cerebrum and above your brainstem. This structure is sometimes referred to as the switchboard of the central nervous system. It relays various sensory information, like sight, sound or touch, to your cerebral cortex from the rest of your body.
  • Hypothalamus: Your hypothalamus sits below your thalamus. It's important in regulating various hormonal functions, autonomic function, hunger, thirst and sleep. Your hypothalamus and pituitary gland are important structures involved in the control of your hormonal system.
  • Pituitary gland: Your pituitary gland sends out hormones to different organs in your body.
  • Basal ganglia: Your basal ganglia are a group of nuclei deep in your cerebrum that is important in the control of your movement, including motor learning and planning.
  • Brainstem nuclei: There are a number of nuclei situated in your brainstem involved in a variety of different functions including cells that give rise to a number of important cranial nerves, normal sleep function, autonomic functions (breathing and heart rate) and pain.
  • Reticular formation: Your reticular formation is a part of your brainstem and thalamic nuclei. These are a part of your reticular activating system (nuclei plus the white matter connecting these nuclei), which lies in your brainstem, hypothalamus and thalamus. The reticular activating system (RAS) mediates your level of awareness, consciousness and focus. They also help control your sleep-wake transitions and autonomic function.

How many brain cells does a human have?

For many years, scientists thought the human brain had 100 billion nerve cells (neurons). Today, we know the actual number is closer to 86 billion.

Your brain contains two types of cells:

  • Neurons send and receive electric nerve signals.
  • Glial cells help maintain your brain, form myelin (a fatty, protective substance found in white matter) and provide nutrition to your brain.

How does your brain relate to hormone production?

Within your thalamus sits a small structure called your hypothalamus. Your hypothalamus is part of your limbic system, which controls your emotions. It sends nerve signals to your pituitary gland. It helps control functions such as:

  • Appetite.
  • Body temperature.
  • Emotions.
  • Hormone production.
  • Sleep and wake cycles.

In your brain, you also have a pineal gland, which secretes the hormone melatonin. Melatonin controls how melanin gives your skin pigment. Melatonin also plays a role in regulating your sleep and wake cycles.

Conditions and Disorders

What conditions or disorders can affect the brain?

About 1 in 6 people have some type of brain condition. There are many types of brain disorders and conditions that vary in severity, including:

  • Alzheimer’s disease and dementia: Progressive loss of cognitive (brain) functions, such as memory, problem-solving or language.
  • Amyotrophic lateral sclerosis (ALS): A neuromuscular disorder where the nerve cells in your brain break down.
  • Autism spectrum disorder (ASD): A developmental disorder that can affect your ability to communicate, regulate behavior or interpret social cues.
  • Brain tumor: Irregular mass of cells that starts in your brain and grows uncontrollably.
  • Epilepsy: A brain disorder that disrupts the activity of your brain’s nerve cells, leading to seizures.
  • Parkinson’s disease: A progressive nervous system disease that often starts with tremors (uncontrollable shakes).
  • Stroke: An interruption of blood supply to your brain, either because of an artery blockage or artery rupture (burst).

Can you be born with a brain condition?

Some babies are born with a brain condition. Inherited conditions, genetic differences or injuries in the womb or at birth can cause these conditions.

Can a head injury cause a brain condition?

Injuries can lead to brain damage. When you experience a blow to your head, you may suffer a traumatic brain injury (TBI) or concussion.

Rarely, severe brain injuries may lead to a condition like epilepsy or dementia. Many people heal from a concussion or brain injury. Repeated head injuries can lead to chronic traumatic encephalopathy (CTE), a condition that causes progressively worsening thinking problems.

Care

What are some tips to keep my brain healthy?

Some lifestyle habits can keep your brain healthier. To support your brain health, you may:

  • Sleep at least seven to eight hours each night.
  • Exercise consistently.
  • Drink alcohol in moderation only.
  • Eat a diet full of vegetables, fruits, whole grains, lean protein and healthy fats.
  • Practice puzzles, such as jigsaw puzzles, crosswords or word searches.
  • Quit smoking.

A strong social network can also improve your brain health. Healthy relationships can help decrease stress, lower your blood pressure and increase your life span.

What should I ask my doctor about my brain health?

You may also want to ask your healthcare provider:

  • What are the signs or symptoms that tell me something could be wrong with my brain?
  • What tests will I have to diagnose a brain condition or injury?
  • What lifestyle changes should I make to improve my brain health?

Frequently Asked Questions

How much does the human brain weigh?

When you're born, your brain weighs about 1 pound. Throughout childhood, your brain grows to about 2 pounds. As an adult, your brain weighs around 2.7 to 3 pounds, depending on your sex and body size.

When does the brain stop developing?

Most brain development happens between birth and your teenage years. But your brain continues developing throughout your 20s. Brain development typically peaks by middle age.

A note from Cleveland Clinic

Your brain is an essential organ that allows you to perceive and interact with the world around you. It receives and interprets all the sensory information you encounter. A range of conditions can affect your brain. You can support your brain health by sleeping well, eating a healthy diet, exercising and making other healthy lifestyle choices. If you suspect that you or a loved one has symptoms related to a brain condition, speak with a healthcare provider.

Last reviewed by a Cleveland Clinic medical professional on 03/30/2022.

References

  • Ackerman S. Discovering the Brain. Washington (DC): National Academies Press (US); 1992. 2, Major Structures and Functions of the Brain. (https://www.ncbi.nlm.nih.gov/books/NBK234157/) Accessed 3/30/2022.
  • American Association of Neurological Surgeons. Anatomy of the Brain. (https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Anatomy-of-the-Brain) Accessed 3/30/2022.
  • American Brain Foundation. Brain Disease. (https://www.americanbrainfoundation.org/diseases/) Accessed 3/30/2022.
  • Johnson SB, Blum RW, Giedd JN. Adolescent Maturity and the Brain: The Promise and Pitfalls of Neuroscience Research in Adolescent Health Policy. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892678/) J Adolesc Health. 2009 Sep; 45(3): 216–221. Accessed 3/30/2022.
  • Mercadante AA, Tadi P. Neuroanatomy, Gray Matter. (https://www.ncbi.nlm.nih.gov/books/NBK553239/) In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Accessed 3/30/2022.
  • Society for Neuroscience. How Many Neurons Are in the Brain? (https://www.brainfacts.org/in-the-lab/meet-the-researcher/2018/how-many-neurons-are-in-the-brain-120418) Accessed 3/30/2022.

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