The Brain: Structures and Divisions

I have always found it interesting how humans seem incapable of producing any mechanism outside of the blueprint of the human body. We, for instance, create computers that almost directly mirror the function and applicability of the human brain. Then we manufacture automobiles that utilize the same processes as our body, albeit with different ingredients, to metabolize fuels. These inventions of human ingenuity illustrate one resounding point; namely, that we have progressed to a point in our evolution where we are capable of not only understanding but reproducing the technology in our bodies, if only on a limited basis. To that end, it would seem a worthwhile exercise to understand the structure of the organ that we utilize in order to understand and reproduce the technology in our bodies, the human brain.

In order to understand the parts of the brain, we must first understand the context in which the brain operates within the body. The body is broken up into several “systems” of which one of the most important is the nervous system. This system of the body encompasses the brain, spinal cord, and the rest of the neural pathways throughout the body. There are two major divisions in the nervous system, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, and the PNS incorporates the neural pathways that extend throughout the body. The spinal cord is basically the link between the brain and the rest of the body; however, the brain itself is the area of the body for which we will be discussing.

The brain is broken up into the two basic sections of the cerebral hemispheres and the brain stem. Within these basic divisions of the brain 5 further sections exist: the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon (Pinel, 2007). The cerebral hemispheres are the largest and most visible section of the brain. This is the gray, wrinkly stuff that we would usually associate with brain matter. The entire region of the cerebral hemispheres, as well as the limbic system, and the basal ganglia are included in the section of the brain named the telencephalon. This section of the brain is most responsible for voluntary movement, processing sensory data, and is the place where learning, speaking, and problem-solving take place. In short, this is where most of the “thinking” takes place. One sub-category of this section is the cerebral hemispheres. The outer layer of this area of the brain is called the cerebral cortex. This is the area where some of the most complicated processes take place, such as language and consciousness (Cerebral Cortex, 2008). Next in the telencephalon is the limbic system, which is implicated in the management of motivated behaviors. These motivated behaviors include fleeing, feeding, fighting, and sexual behavior. The limbic system can be broken up into two cortical (meaning of the cortex) structures, the hippocampus, and the cingulate cortex; and four sub-cortical structures, the mammillary bodies, the amygdala, the fornix, and the septum. The last section of the telencephalon, the basal ganglia, largely deals with voluntary movement. The sub-cortical structures of the basal ganglia include the long tail-like caudate and the putamen which is collectively referred to as the striatum, and the globus pallidus.

Now that the largest and most prominent section of the brain has been covered, we will move on to the underbelly, as it were, of the brain. Moving from top to bottom, the next section of the brain is called the diencephalon. The thalamus and hypothalamus are the only two structures in the diencephalon. The thalamus is a two-lobed organ that projects sensory signals from the sensory organs into the sensory cortex. The other structure contained in the diencephalon is the hypothalamus which regulates many motivated behaviors. The hypothalamus also contains three other structures named the optic chiasm, the pituitary gland, and the mammillary bodies. The optic chiasm is where both optic nerves from the eyes come together in the brain. The hypothalamus controls the pituitary gland partially through hormones such as LH-releasing hormone and FSH-releasing hormone (Finchner-Rathus, Nevid, Rathus, 2005).

Next down the ladder is the mesencephalon which contains the two primary divisions: tectum and tegmentum. The tectum occupies the dorsal side of the mesencephalon region and contains two bumps called the inferior colliculi and the superior colliculi. The inferior colliculi have an auditory function, and the superior colliculi have a visual function. On the other hand, the tegmentum sits ventrally to the tectum and contains many structures such as the reticular formation, the tracts of passage, the periaqueductal gray, the cerebral aqueduct, the substantia nigra and the red nucleus. The substantia nigra plays a part in the sensorimotor system, and the periaqueductal gray is involved in the pain-reducing effects of opiate drugs (i.e. morphine and heroin).

Moving on, the metencephalon incorporates both the pons, which is just a bulge of descending tracts and part of the reticular formation and the cerebellum, which is an important sensorimotor structure. The cerebellum has been called the little brain because it looks like a small brain next to the larger cortex. The cerebellum helps us control our movements and to adapt our movements in cases of changing conditions.

Lastly, the myelencephalon contains mostly tracts that carry signals between the brain and the rest of the body. This section could be described as the bridge, if you will, between the spinal cord and the rest of the brain. Of particular interest to biopsychology is the reticular formation which is involved in quite a few areas of mental coordination. The areas include “…sleep, attention, movement, the maintenance of muscle tone, and various cardiac, circulatory, and respiratory reflexes” (Pinel, 2007, 52). The reticular formation also seems to play some part in arousal which is why it is sometimes called the reticular activating system.

In conclusion, a better understanding of the structures and sections of the human brain help shed light on how the brain functions and in what way it interacts with the rest of our body. It is through this understanding of the brain that we might one day be able to understand how we can duplicate our own bodily technology rather than just that we can duplicate our bodily technology.


Cerebral cortex. (2008). Retrieved June 5, 2008, from the Wikipedia Web site:

Finchner-Rathus, L., Nevid, J.S., Rathus, S.A. (2005). Human sexuality in a world of diversity, sixth edition. Boston, MA: Allyn & Bacon.

Pinel, J.J. (2007). Basics of biopsychology. Boston, MA: Allyn & Bacon.


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