Brain: How It Works, Function, Parts & Conditions (2024)

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.