The human body is an amazingly complex thing, and the gray matter that lives in your skull controls it all, from the breaths you take to the beat of your heart. Your brain is a biological computer, storing information for later recall and keeping your favorite memories safe. Let’s take a closer look at the structure of the human brain, and what each different part controls.
Introducing the Brain
Human beings have the largest brain in relation to our body size, and the most complex. On average, your brain will weigh about 3.3 pounds and contain more than 86 billion neurons. We call our brain gray matter, but it’s made up of two colors — gray and white. Gray matter consists of those neurons that we just mentioned. White matter includes axons and dendrites — billions of nerve fibers that thread their way through the brain. Then you’ve got synapses, the little bridges that connect your neurons to form your brain.
Let’s take a closer look at the structure of the biological computer that keeps your body running.
The most substantial part of your brain is the cerebrum. It makes up the outer layer of your brain. This is the part that you usually see when you’re looking at a picture or a model of the brain. If you look at the cerebrum, you can see that there are two distinct sides, which scientists refer to as the right and left hemispheres.
Scientists believe the left hemisphere controls the more analytical aspects of your thought processes. If you’re good at math, linear thinking and logic puzzles, you’re designated as left-brained. The right hemisphere supposedly controls the more emotional aspects of your psyche — creativity, arts and imagination. If you like to draw or tell stories, you’re considered more right-brained. This theory has been around since the 1960s, and while scientists have disproved it in recent years, it’s fun to think of yourself as right- or left-brained, depending on where your skills lie.
The cerebrum is made up of four lobes — frontal, temporal, occipital and parietal — which we’ll discuss in more detail in a moment.
The Corpus Callosum
The corpus callosum lies between the two hemispheres of the cerebrum, holding them together. This thick band of nerve fibers connects the regions and allows them to communicate with one another. There are four parts of the corpus callosum — the rostrum, genu, body and splenium. The genu and rostrum connect the frontal lobes of each hemisphere. The splenium and body connect the temporal and occipital lobes on either side of the brain.
It also helps our brain process information from the two different sides of our body. The body and splenium that connect the occipital lobe allow each hemisphere to process images seen by their respective eye. If you have someone stand behind you and poke you in the back, you can locate the touch because of the corpus callosum.
The corpus callosum can even be severed, in what is known as a corpus callosectomy. This procedure is an extreme treatment for epilepsy. While the patient can survive and live a full life, this surgery does have adverse effects, such as split brain syndrome.
The Cerebral Cortex
The cerebral cortex is what gives the structure of the human brain its iconic wrinkled look. It is a thin layer that covers the cerebrum and is usually between 1.5 and 5 millimeters thick. Its surface consists of billions of nerves, which is what creates its gray color. The bulges in the cerebral cortex are known as gyri, and the furrows or fissures these gyri form are known as sulci.
In spite of being such a thin part of the brain, the cerebral cortex controls your brain’s language functions. If you can understand the words on this page and have the ability to speak in your native language, then your cerebral cortex is doing its job. It also controls your intelligence and your personality and gives you the ability to plan, organize and understand the sensations created by touch.
The cerebral cortex also extends to cover the cerebellum.
If the cerebrum is the largest part of your brain, the cerebellum comes in a close second. Like the cerebrum, it also has two hemispheres and sits beneath the cerebrum on top of the brainstem. It is part of the hindbrain and controls things like balance, posture and coordination. If you can stand up from reading this article and walk around the room without falling, thank your cerebellum.
The Frontal Lobe
The front of your brain, just behind your forehead, is called the frontal lobe. It also takes the longest to mature, so your frontal lobe is still growing and making new connections well into your early adult years. This lobe is in charge of a variety of higher cognitive functions, like:
- Coordinated movement: While the cerebellum handles balance, the frontal lobe lets you do more than one thing at a time, such as picking up something from the floor as you’re walking across the room. It also enables you to rub your stomach and pat your head at the same time.
- Judging consequences: The frontal lobe lets you think ahead and determine the future consequences of your current actions.
- Noticing similarities: If you see two pictures and can pick out the similarities between them, that’s your frontal lobe at work. If someone sees you and says you look just like your mom or dad, that’s their frontal lobe working too.
- Forming long-term memories: Emotional short-term memories become long-term ones in the frontal lobe.
- Empathy: It’s thought that empathy, or being able to experience the emotions of others and put yourself in their shoes, is due to the frontal lobe.
Dopamine plays a considerable role in the frontal lobe as well, because that’s where your brain’s reward system is. Most of your dopamine-sensitive neurons reside in the frontal lobe.
The Parietal Lobe
The parietal lobe sits on top of the temporal lobe, in the middle of the brain between the frontal and occipital lobes. This lobe is in charge of things like speech, regulating your five senses, handwriting, body position and movement. It’s also responsible for helping you sense things like touch, pain and pressure. Problems with the parietal lobe often manifest as conditions like aphasia — choosing the wrong words when you’re trying to speak — getting lost when trying to find a new place or even having trouble with delicate movement.
The Temporal Lobe
The temporal lobe hangs out toward the bottom of the cerebrum, just above the cerebellum. This lobe handles everything from memory to sensory input and language. If you can comprehend what you’re reading right now, thank your temporal lobe, because it also helps you understand the data you’re receiving from your five senses.
The Occipital Lobe
The occipital lobe might be the smallest one, but it is one of the most important. It acts as the visual center for your brain. In spite of being located at the back of your skull, just above the cerebellum, the occipital lobe processes the visual stimuli that comes from your eyes. It’s a lot more complicated than it sounds. If you see something, your brain isn’t just taking a picture of the object — it’s comparing it to other things, judging how far away it is, taking in its color and shape, and estimating its relative size.
The Limbic System — Amygdala, Hippocampus, Basal Ganglia, Cingulate Gyrus, Ventral Tegmental Area and Prefrontal Cortex
The brain’s limbic system refers to a bunch of different structures within the organ itself. The amygdala manages emotional responses and aggression. If you are afraid of something or happy to see someone, that’s your amygdala in action.
The hippocampus looks like two horns in the brain, attached to the amygdala. Without your hippocampus, your mind can’t convert short-term memories into long-term ones. You’ll end up living out the Adam Sandler movie “50 First Dates!”
The basal ganglia help you focus your attention on the task at hand, and are necessary when you’re performing repetitive behaviors. Brushing your teeth every morning and evening is the purview of the basal ganglia.
The cingulate gyrus sits right above the corpus callosum and connects the thalamus to the hippocampus. If you have a memory that you associate with a scent or with pain, it formed in your cingulate gyrus.
The ventral tegmental area of the brain consists almost exclusively of dopamine pathways. This area ties into your brain’s pleasure center and may play a role in addictive behaviors.
The prefrontal cortex is a part of the frontal lobe, but so closely linked to the limbic system that scientists consider it part of both. The prefrontal cortex also consists of dopamine pathways, which means it might play a role in addiction, but it also gives you the ability to think about the future, make plans and then act on them.
The Diencephalon — Epithalamus, Thalamus, Subthalamus and Hypothalamus
The diencephalon contains four different sections — the epithalamus, thalamus, subthalamus and hypothalamus.
The epithalamus is a bridge between the limbic system and the rest of the brain. It works with the pineal gland to control your circadian rhythm and can help regulate the pathways that control motor function and emotion.
The hypothalamus controls most of your brains’ autonomic function. It controls hormones and body temperature, and works with the rest of the diencephalon to regulate your sleep cycles. If you feel hungry or thirsty, that is your hypothalamus telling you that your body needs food or water.
The subthalamus helps you move by regulating the motion of your skeletal muscles. It also acts as a bridge between other parts of the diencephalon.
The thalamus is an information switchboard, relaying information between the cerebral cortex and subcortical areas of the brain. It controls when you sleep, when you’re awake and might even be connected to your consciousness. Without your thalamus, your mind doesn’t know when to wake up, leaving you in a coma.
The Brainstem — Midbrain, Pons and Medulla Oblongata
The brainstem serves the critical role of transmitting the signals from your brain to the spinal cord, and from there into the rest of your body. Without the brainstem, your brain would be sending commands with nowhere for them to go. It includes three major components — the midbrain, the pons and the medulla oblongata.
The midbrain serves to connect the brain’s three sections — fore, mid and hindbrains. The pons and medulla oblongata are considered parts of the hindbrain. These two areas handle autonomic functions like breathing and blood pressure.
The Glands — Pituitary and Pineal
There are two major glands in the brain that we’re going to mention here — the pituitary and pineal glands.
The pituitary gland works with the hypothalamus to secrete the hormones that your body needs to function, including:
- Estrogen, testosterone and progesterone. The amount of each will depend on the gender of the individual.
- Prolactin, which stimulates milk production in nursing mothers
- Thyroid hormones for metabolism
- AdrenoCorticoTropic hormones, which tell the adrenal gland to release adrenaline
- Melanocyte hormones, which change skin pigmentation
- Human growth hormones
- Vasopressin, which encourages the body to retain water
The pineal gland secretes melatonin, which regulates your body’s circadian rhythm.
Your Amazing Brain
The structure of the human brain is a marvel. When damaged, it can grow new pathways and restore lost skills. It continues to grow and change, from the moment we’re born until the moment we die, creating new paths as you learn new information and make memories. The next time you look in the mirror, think about all these parts of the brain and how they work together to make you the person you are today.