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The 3 Major Parts of the Brain and What They Do

Posted by Brittany Logan | Dec 26, 2019 2:00:00 PM

General Education

 

Brain Illustration- Edited

Mission control. Command center. Control tower. No, I’m not talking about space or your laptop hard drive, or even airport flight control. I’m talking about the human brain—the most complex and essential organ our bodies have. What is the brain structure? What part of the brain controls emotions?

Whether you’re studying it in class, preparing for an AP exam, or just curious about brain structure, in this article, you’ll learn about the main parts of brain anatomy and their functions and as well as get a general overview of the brain’s supporting cast.

 

What Is the Brain and Why Does It Matter?

The brain is a three-pound organ that serves as headquarters for our bodies. Without it, we wouldn’t be able to process information, move our limbs, or even breathe. Together with the spinal cord, brain structure and function helps control the central nervous system—the main part of two that make up the human nervous system. (The other part, the peripheral nervous system, is made up of nerves and neurons that connect the central nervous system to the body’s limbs and organs.) The human nervous system is responsible for helping us think, breathe, move, react and feel.

 

Body-Brain Connection

Like any good command center, there is a structure to the brain and its operations that help it carry out its basic functions.

 

What Are the Main Parts of the Brain?

There are three main parts of the brain: the cerebrum, cerebellum and the brain stem.

Parts of Brain Diagram- 3 parts

Denise Wawrzyniak/Wikimedia Commons

 

What Is the Cerebrum?

Cerebrum_animation_small- Was A Bee

Was I A Bee/Wikimedia Commons

 

The cerebrum is the largest part of the brain. Located in the front and middle part of the brain, it accounts for 85% of the brain’s weight. Of the three main parts of the brain, the cerebrum is considered the most recent to develop in human evolution. The cerebrum is responsible for all voluntary actions (e.g.: motor skills), communication, emotions, creativity, intelligence and personality.

 

What Are the Main Parts of the Cerebrum?

The cerebrum’s structure is made up of:

Table- cerebrum structure Eqtn

What Are the Layers of the Cerebrum?

The cerebrum has two layers: one inner and one outer. The outer layer is known as the cerebral cortex (represented in red in the spinning image above). Most times, whenever you see photos of the brain, you are looking at the cerebral cortex. This area houses the brain’s “gray matter,” and is considered the “seat” of human consciousness. Higher brain functions such as thinking, reasoning, planning, emotion, memory, the processing of sensory information and speech all happen in the cerebral cortex. In other words, the cerebral cortex is what sets humans apart from other species.

Table- Cerebrum Cortex Functions

The cerebral cortex is referred to as “gray matter,” due to its color and is responsible for several vital functions, such as those listed above.

 

What Is the Corpus Callosum?

The cerebrum’s inner core houses the brain’s “white matter.” The major part of the inner core is known as the corpus callosum. The corpus callosum is a thick tract of fibrous nerves that serve as a kind of switchboard enabling the brain’s hemispheres to communicate with one another. Whereas the cerebral cortex is the cerebrum’s outer layer made up of gray matter, and is responsible for thinking, motor function and information processing; the corpus callosum is the cerebrum’s inner core, made up of white matter, with four parts of nerve tracts connecting to different parts of the hemispheres.

Corpus_callosum- Life Sciences Wiki

Home of the white matter: corpus callosum./Life Sciences Database/Wikimedia Commons

 

The corpus callosum’s nerve fibers (or axons) are coated with myelin. This fatty substance helps increase the transmission of information between the next part of the cerebrum: the two hemispheres.

 

The Cerebrum's Left and Right Hemispheres

In addition to two layers, the cerebrum also has two halves, or hemispheres: the left hemisphere and the right hemisphere. Although each hemisphere is known for managing different functions, it is important to note that both handle most processes of the brain structure.

The existence of the hemispheres is vital to our body’s functions. The relationship between our brain and body is contralateral. This means, generally speaking, that the left side of the brain (left hemisphere) controls the right side of the body, and the right side of the brain (right hemisphere) controls the left side of the body. Because the hemispheres carry out different tasks, they need to “talk” to one another in real time to coordinate our movements, thoughts, etc.

The left hemisphere is responsible for controlling the right side of the body. It handles language, reasoning, logic and speech. If the left hemisphere were a set of classes in school, it would be your math, science, and English classes.

The right hemisphere is responsible for controlling the left side of the body. It handles spatially-related tasks and visual understanding. In terms of classes, the right hemisphere would be your arts, music, and creative writing classes. 

 

Left Brain RIght Brain Functions

            The deep groove separating the hemispheres is called the longitudinal fissure (or, cerebral fissure).

 

The longitudinal fissure is prevented from completely splitting the cerebrum in half by the corpus callosum. Thanks to the corpus callosum (our brain’s speedy switchboard), the left side of your brain can chat instantaneously with the right side of your brain.

 

Longitudinal_fissure_of_cerebrum

The red line down the center of the cerebrum is the longitudinal fissure./Life Sciences Database/Wikimedia Commons

 

All this hemisphere talk brings us to the final part of the cerebrum: the four lobes.

 

What Are the 4 Lobes of the Brain?

 

Lobes- four

Database Center for Life Sciences/Wikimedia Commons

 

The cerebrum’s left and right hemispheres are each divided into four lobes: the frontal, parietal, occipital and temporal lobes. The lobes generally handle different functions, but much like the hemispheres, the lobes don’t function alone. The lobes are separated from each other by depressions in the cortex known as sulcus (or sulci) and are protected by the skull with bones named after their corresponding lobes.

 

Lobes 2- Cancer Rsrch UK

Cancer Research UK/Wikimedia Commons

 

The frontal lobe is located in the front of the brain, running from your forehead to your ears. It is responsible for problem-solving and planning, thought, behavior, speech, memory and movement. The frontal lobe is separated from the parietal lobe by the central sulcus and is protected by a singular frontal skull bone.

The parietal lobe picks up where the frontal lobe ends and goes until the mid-back part of the brain (about where a ponytail would be). It is responsible for processing information from the senses (touch, sight, hearing, smelling and sight), as well as language interpretation and spatial perception. It is separated from the other lobes on all four sides: from the frontal lobe by central sulcus; from the opposite hemisphere by the longitudinal fissure; from the occipital lobe by parieto-occipital sulcus; and from the temporal lobe below by a depression known as the lateral sulcus, or lateral fissure. Because each hemisphere has a parietal lobe, there are two parietal skull bones—one on the external side of each hemisphere.

The occipital lobe is located in the back of the brain. It is considered the brain’s “visual processing center” because it’s where the bulk of information our eyes take in gets analyzed and sorted. It is separated from the parietal lobe by the parieto-occipital sulcus; from the temporal lobe by the lateral occipital sulcus; and from the cerebellum (the second part of the brain, coming up soon) by what is called the cerebellar tentorium (or tentorium cerebelli). It is protected by the skull’s singular occipital bone.

The temporal lobe is located in behind and below the frontal lobe (and beneath the parietal lobe), under the lateral fissure. It is responsible for our memory, emotions, language and speech, and auditory and visual processing. It is separated from the parietal and frontal lobe by the lateral sulcus (lateral fissure); from the occipital lobe by the lateral occipital sulcus and occipitotemporal sulcus; and is adjacent to the corpus callosum. Similar to its parietal neighbor, the temporal lobe is protected by two bones—one temporal bone on the external side of each hemisphere.

Lobes 1

The brain’s lobes serve as a map for understanding where brain functions happen./Denise Wawrzyniak/Wikimedia Commons

 

What Is the Cerebellum?

Cerebellum_animation_small- Was a bee

Was I A Bee/Wikimedia Commons

 

The cerebellum stands for “little brain” in Latin. It looks like a separate mini-brain behind and underneath the cerebrum (beneath the temporal and occipital lobes) and above the brain stem. The cerebellum (along with the brain stem) is  considered evolutionarily to be the oldest part of the brain.

Where the cerebrum makes up 85% of the brain’s mass, the cerebellum takes up only 10%. However, the cerebellum accounts for more than half of the brain’s neurons. The cerebellum is responsible for voluntary movements, coordination, balance, posture, muscle tone, and cognitive functions.

 

What Are the Main Parts of the Cerebellum?

The cerebellum’s structure is made up of:

Table- Cerebellum Structure Eqtn

The Cerebellum's Inner and Outer Layers

Like the cerebrum, the cerebellum has two layers: one inner and one outer. The outer layer is called the cerebellar cortex. Like the cerebral cortex, it is full of gray matter. Functions such as movement, motor learning, balance and posture happen here.

Underneath the cortex lies the cerebellum’s white matter. Called “arbor vitae” ("tree of life") for its appearance, the cerebellum’s white matter contains cerebellar nuclei. These neurons are vital because they relay information between the cerebral cortex and the peripheral nervous system to assist in learning and cognitive functions, motor control, balance and coordination. (In a very loose parallel, both the cerebellar nuclei of the cerebellum and the corpus callosum of the cerebrum are responsible for internal communications: The corpus callosum relays messages between there cerebrum’s hemispheres, and the cerebellar nuclei relays messages between the body and cerebrum.)

 

The Cerebellum's Left and Right Hemispheres

The cerebellum also has two hemispheres: the left cerebellar hemisphere and the right cerebellar hemisphere. Just as the longitudinal fissure divides the cerebrum’s hemispheres, the “vermis” (Latin for “worm”) separates the cerebellum’s hemispheres.

 

Cerebellar hemisphere 1- spinning animation

The Database Center for Life Science/Wikimedia Commons

 

Cerebellar hemisphere 2- animation       Cerebellar hemisphere 3- animation

Cerebellar hemispheres seen from front (r) and back (l)/ The Database Center for Life Science/Wikimedia Commons

 

What Are the Three Lobes of the Cerebellum?

The cerebellum’s hemispheres are each divided into three lobes: the anterior lobe, posterior lobe, and the flocculonodular lobe. These lobes are split up by two fissures (grooves), called the primary fissure and the posterolateral fissure.

 

Cerebellum- 3 Lobes- Animation         Cerebellum- 3 Lobes- Non-Animation

The three lobes of the Cerebellum, where purple is the anterior lobe, green is the posterior lobe and orange is the Flocculonodular lobe./Database Center for Life Science/Wikimedia Commons

 

Unlike the cerebral cortex, there are no clear separation of functions in the cerebellar cortex. The best way to identify the tasks are by the information each section processes.

 

Spinocerebellum

Cerebellar hemisphere-Anterior_lobe animation spinning 1

The Database Center for Life Science/Wikimedia Commons

 

The anterior lobe and the vermis together are known as the spinocerebellum. The spinocerebellum helps regulate muscle tone and body movement. It’s also responsible for our sense of our body’s position in relation to our surroundings, and in relation to other parts of our body (a.k.a.: proprioceptive information). This area receives input from our spinal cord, auditory and visual systems.

 

Cerebrocerebellum

Cerebellar hemisphere-Posterior_lobe animation spinning 2

The Database Center for Life Science/Wikimedia Commons

 

The posterior lobe (the cerebellar hemispheres at large, not including the vermis and anterior lobe) is called the cerebrocerebellum. This area is responsible for planning movements that are about to happen, managing sensory information to determine action and motor learning. It receives information from the cerebral cortex (the parietal lobe).

 

Vestibulocerebellum

 

Cerebellum-Flocculonodular_lobe_-_animation- WIki LSDB         Cerebellum-Flocculonodular_lobe_still WIki LSDB

The Database Center for Life Science/Wikimedia Commons

 

The flocculonodular lobe is referred to as the vestibulocerebellum. This area is responsible for managing our eye movement and balance. Unlike the other two areas, this one gets data directly from a sensory nerve, the vestibular nerve. (The vestibular nerve is connected to the vestibular system, which is responsible for our sense of balance and spatial orientation.) This area receives information from the visual cortex.

 

What Are the Four Nuclei of the Cerebellum?

As the three lobes take in information from the cerebrum, spinal cord and body, the cerebellum also has a way of sending out information. This is done through what are called nuclei—a bundle or neurons embedded deep in the cerebellum’s white matter.

Rounding out cerebellum’s composition are the four nuclei that pass information between the cerebrum and the body. These nuclei are: dentate, emboliform, globose, and fastcgi. They receive on the body and give information from the cerebellum through Purkinje cells (neurons) and mossy fibers. 

 

What Is the Brain Stem?

Brainstem_animation- Wiki Life Sciences Databases

Life Sciences Database/Wikimedia Commons

 

The final section of the brain is a mass of tissue and nerves called the brain stem. Located underneath the cerebrum and cerebellum, the brain stem connects the brain to the spinal cord. All information that goes from the brain to the body (or vice versa), must pass through the brain stem to reach its destination. The brain stem accounts for the remaining 5% of the brain’s mass, and is (along with the cerebellum), the oldest part of the brain. The brain stem is responsible for regulating the heart and lungs, communications between the brain and the peripheral nervous system (the nerves of the body), our sleep cycle, and coordinating reflexes.

Spinal Cord as Plug to Brain

The brain stem plugs the brain (central nervous system) into the rest of the body through the spinal cord (peripheral nervous system).

 

Running throughout the brain stem is an area known as the “reticular formation.” This collection of nuclei plays a vital role in managing our consciousness (e.x.: sleep and alertness) and connecting with the various motor nerves to help us move our heads and faces, regulate our involuntary actions, and to help us chew, eat, breathe and see.

 

What Are the Main Parts of the Brain Stem?

The brain stem is made up of three parts: the midbrain, the pons and the medulla.

 

Brain Stem- All Diagram Wiki BruceBlaus

BruceBlaus/Wikimedia Commons

 

Midbrain

Brain Stem- Midbrain- Wiki LSDB

Life Sciences Database/Wikimedia Commons

 

The midbrain is located underneath the cerebral cortex, near the top of the brain stem. It connects the cerebrum to the brain stem. The midbrain helps process visual and auditory information, such as controlling the eyes and eyelids. It also plays a role in regulating our body temperature and motor movements.

Main Parts of the Midbrain

Table- Tectum & Tegmentum

 

Pons

Brain Stem- Pons- Wiki LSDB

Life Sciences Database/Wikimedia Commons

 

Pons is the Latin word for “bridge.” The pons is responsible for connecting the brain stem to the cerebral cortex and the cerebrum to the cerebellum. It can be found right underneath the midbrain and above the medulla oblongata. Although it is the largest section of the brain stem, the pons is only about 2.5 centimeters long. The pons is responsible for assisting in motor functions, particularly for nerves in the face, ears, and eyes. It also plays a role in regulating the intensity and frequency of breathing. It has both gray and white matter, but it does share gray matter with the midbrain. The reticular formation of the pons’ gray matter plays a vital role in dreaming and REM (deep) sleep.

 

Medulla Oblongata

Brain Stem- Medulla Oblongata- Wiki LSDB

Life Sciences Database/Wikimedia Commons

 

The medulla oblongata is located behind and partially underneath the cerebellum. It is responsible for our life-sustaining involuntary (autonomic) actions such as breathing, regulating the heartbeat and blood pressure, and reflexes such as sneezing, vomiting and coughing.

Like the pons, the medulla also has gray and white matter. Some of its white matter is shared with the spinal cord, while its gray matter processes cranial nerve information. The reticular formation in the medulla’s gray matter assists with breathing and controlling the heart rate.  

 

 

The Cerebellar Peduncles

Earlier, we learned how four nuclei are responsible for connecting the cerebellum to the body. To connect the cerebellum to the brain stem, the brain depends on nerve tracts called cerebellar peduncles. The cerebellar peduncles help process and analyze motor and sensory information, such as the position of our joints and limbs. There are six cerebellar peduncles (three for each hemisphere) with both white and gray matter. The six cerebellar peduncles are: superior (2), middle (2) and inferior (2).

 

 

What Are the Regions of the Brain and How Do They Fit Into the Brain Structure?

The three main parts of the brain are split amongst three regions developed during the embryonic period: the forebrain, midbrain and hindbrain. Together, these regions act as a useful map to understanding the various parts of the brain’s structure and functions.

 

Mid, Fore & Hindbrain- BruceBlaus- Edited

The forebrain, midbrain and hindbrain serve as regions that make finding the various parts of the brain easier./ BruceBlaus/Wikimedia Commons

 

To better understand the roles of the forebrain, midbrain and hindbrain within the brain, check out the short video below:

 

 

The Brain’s Support System

While we’ve covered the basics of brain anatomy, there are a few other supporting players that assist the brain in its role as our command center.

Protective cushioning

 

Skull animation- arielinson Wiki

Arielinson/Wikimedia Commons

 

The brain is surrounded by the cranium, or skull. The skull’s job is to house the brain and protect its soft tissue from trauma and the elements. The skull is made up of 22 bones, along with fibrous joints called sutures, that keep the brain safe from external injury.

 

Meninges

Cushioning the brain from the skull are the meninges. The meninges are three layers of tissue known as the dura mater, arachnoid & pia mater. These layers protect the brain from being displaced; separate the cerebrum from the cerebellum; transfer food and waste from the brain to the body; and clean the brain’s fluid to keep it running.

 

Everything Else- Meninges

 

Food and Waste Transport

The cerebrospinal fluid is responsible for bringing in nutrients and removing waste in the brain and spinal cord. It is found in the meninges layers and is moved through the brain by ventricles.

The brain’s four main ventricles (spaces) help the cerebrospinal fluid nourish and cleanse the brain. They also cushion the brain from injury.

 

Information Transport and Boundary Assistants

The gyrus (plural: gyri) and sulcus (sulci) are what give the brain its wrinkly appearance. The grooves (or fissures) of the brain are known as the sulci, while the bumps (or ridges) are called the gyri. These folds and ridges help increase how much of the cerebral cortex can fit into the skull. They also create boundaries between the different sections of the brain, such as the two hemispheres and four lobes of the cerebrum.

Everything Else- Gyrus & sulcus

Albert Kok/Wikimedia Commons

 

Blausen_0115_BrainStructures- BruceBlaus- Edited

The gyri and sulci create the wrinkles we traditionally associate with the brain./ Bruce Blaus/Wikimedia Commons

 

Arteries

The heart pumps blood to the brain through two arteries: the carotid and vertebral. Because of the brain’s importance to the body and the fact that brain cells die without constant blood flow, the heart sends about 20% of the body’s bloody supply to the brain. The blood brings oxygen and other nutrients the brain needs to regulate itself and function properly.

Screen Shot 2019-09-10 at 9.21.35 PM

The heart pumps blood in and out of the body through the carotid and vertebral arteries.

 

Neurons and Glial Cells

The human brain has about 80-100 billion neurons, and roughly the same of glial cells. Neurons and glial cells help coordinate and transport signals within the human nervous system. While neurons communicate and receive information with cells, glial cells protect and support neurons in completing their mission.

 

Neurons & Glial Cells

NIH

 

Cranial Nerves

Twelve cranial nerves help transport information from the brain and body. These motor and sensory nerves are part of the peripheral nervous system and are responsible for controlling muscles and processing information from the organs and bringing it to the brain. These include our senses of sight and smell, as well as our balance and hearing.

The twelve nerves are named for their function and include: the olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, spinal accessory nerve, and hypoglossal nerve.

 

In Conclusion: Brain Anatomy

The human brain is an incredibly complex, hardworking organ. As one-half of the human nervous system, the brain structure oversees nearly all of the body's operations, including how we move, think, feel and understand ourselves and the world around us. And knowing all this brain anatomy is important. From the cerebrum, cerebellum and the brain stem, to all the parts in between: this three-pound organ is what makes us humans, well, human.

 

What’s Next?

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Brittany Logan
About the Author

Brittany Logan graduated from Columbia University Graduate School of Journalism with a Master of Science with Honors. She has a dual-degree Master's from Sciences Po School of Journalism in Paris, and earned her Bachelor’s in Global Studies from the University of California, Santa Barbara. She has spent several years working in higher education- including as an English teacher abroad and as a teaching assistant in science writing at Columbia University’s Earth Institute.



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