Five Major Structures of the Brain

“In order to understand what the brain does, it is first necessary to understand what it is – to know the names and locations of its major parts and how they are connected to one another” (Pinel, 2011. p. 51). The five major structures that compose the brain are labeled as myelencephalon, metencephalon, mesencephalon, diencephalon, and telencephalon. These major structures are what create the adult forebrain, midbrain, and the hindbrain. First, the myelencephalon is also known as the medulla. The myelencephalon carries signals between the brain and the body through tracts that compose the posterior division of the brain. In addition, in the latter part of the myelncephalon to the front part of the midbrain is where the reticular formation is located. The reticular formation is composed of a “…complex network of about 100 tiny nuclei…” (Pinel, 2011. p. 64).

Furthermore, the reticular formation has many functions that include sleep, movement, attention, the maintenance of muscle tone, and a number of cardiac, circulatory, and respiratory reflexes. Next, the metencephalon is similar to the myelencephalon, where it “…houses many ascending and descending tracts and part of the reticular formation” (Pinel, 2011. p. 65). The tracts located in the metencephalon make up the pons – a bulge located on the ventral surface of the brain stem. Along with the pons, the cerebellum, also known as the little brain, is a large structure located on the dorsal surface of the brain stem. The cerebellum is an important sensorimotor structure, however is not limited to sensorimotor control. Following the metencephalon is the mesencephalon, which has two different divisions described as the tectum and the tegmentum.

The tectum, also known as the optic tectum, is the division on the dorsal surface of the midbrain, and is composed of two pairs of colliculi. First, inferior colliculi at the posterior, are for auditory functions. Next, the superior colliculi, at the anterior, are for visual functions. Conversely, the tegmentum is made up of three colorful structures; the periaqueductal gray, the substantia nigra, and the red nucleus. Pinel (2011) discusses that “the periaqueductal gray is the gray matter situated around the cerebral aqueduct, the duct connecting the third and fourth ventricles; it is of special interest because of its role in mediating the analgesic (pain-reducing) effects of opiate drugs” (p. 65). Also, Pinel (2011) discusses that “the substantia nigra…and the red nucleus are important components of the sensorimotor
system” (p. 65).

Subsequent to the mesencephalon is the diencephalon that is made up of the thalamus and the hypothalamus. To begin with, the thalamus is at the top of the brain stem, and is a large two-lobed structure that contains different pairs of nuclei. The sensory relay nuclei are the nuclei that researchers understand the most. Pinel (2011) discusses that the sensory relay nuclei “…receive signals from sensory receptors, process them, and then transmit them to the appropriate areas of sensory cortex” (p. 66). Next is the hypothalamus, which is below the anterior thalamus. The hypothalamus helps regulate the motivated behaviors; such as sleep, eating, and sexual behavior. Furthermore, the pituitary gland, which regulates the release of hormones, is located dangling from the hypothalamus on the ventral surface of the brain.

However, there are two other structures, the optic chiasm and the mammillary bodies, which are on the inferior surface of the hypothalamus. The optic chiasm is where each eye comes together, and the mammillary bodies are considered to be a part of the hypothalamus. Following the diencephalon is the telencephalon. The telencephalon facilitates the brain’s most compound functions; such as interpreting sensory input, initiating voluntary movement, and mediating complex cognitive processes. Some complex cognitive processes are as follows – learning, problem solving, and speaking (Pinel, 2011. p. 66). To understand the brain, one must understand what the brain is composed of, five different divisions, and the major functions of those divisions.

First, the myelencephalon has a variety of functions, for a few examples, the maintenance of muscle, sleep, attention, and respiratory reflexes. Next, the metencephalon and mesencephalon are important to the sensorimotor system. Then, the diencephalon plays a role in the visual, auditory, and somatosensory systems. Last, the telencephalon initiates voluntary movement, mediates the cognitive processes such as learning, problem solving, and speaking, and interprets sensory input. Without understanding these five divisions, one cannot fully understand what causes a person to see, learn, say, or do something.

References:
Pinel, J. P. J. (2011). Biopsychology (8th ed.). Boston, MA: Pearson.