The Brain

The Five Major Structures of The Brain

At the beginning of birth there are initially three swellings in the human brain. Once adulthood is reached the brain develops two new swellings. The forebrain and the hindbrain grow into two different swellings, this is how two more are added while becoming an adult.
Once as an adult the brain consists of five structures that make up the fore, mid, and hindbrain from anterior to posterior. These five structures are the Telencephalon, the Diencephalon, the
Mesencephalon (mid-brain), the Metencephalon, and the myelencephalon.

Myelencecephalon

The Myelencephalon is the posterior part of the brain, also known as the medulla. It is

composed largely of tracts carrying signals between the brain and the rest of the body. An

interesting part of the Myelencephalon is called the reticular formation. Reticular formation is a

complex network of around 100 tiny nuclei that occupies the central core and also the brain stem

from the posterior boundary of the Myelencephalon to the anterior boundary of the midbrain.

This part of the brain even plays a role in arousal which is why it is sometimes referred to as

reticular activating system. However, this term can be misleading because the nuclei of the

reticular formation are involved sleep, attention, movement, the maintenance of muscle tone, and

various cardiac, circulatory, and respiratory reflexes.

Metencephalon

The Metencephalon is much like the Myelencephalon as they both house many ascending

and descending tracts and forms part of the reticular formation. These structures create buldges which are referred to as pons which is located on the brain stems ventral surface. The other

major division of the Metencephalon is the cerebellum. This is the large convoluted structure of

the brain stems dorsal surface, it is an important sensorimotor structure. Cerebellar damage

eliminates the ability to precisely control one’s movements and for them to adapt to changing

conditions. Cerebellar damage also can produce a variety of cognitive deficits which affect

decision making and use of language. This suggests that the cerebellum and it’s functions are

not restricted by sensorimotor control.

Mesencephalon

The Mesencephalon is like the Metencephalon is the sense that they have two divisions,

these two divisions are tectum and the tegmentum. The tectum is the dorsal surface of the

midbrain. In mammals, the tectum is composed of two pairs of bumps, the colliculi. The

inferior colliculi, which is the posterior pair, have an auditory function. The anterior pair called

the superior colliculi has visual function. However, in lower vertebrates, the function of the

tectum is entirely visual. This is why the tectum is sometimes referred to as the optic tectum.

The tegmentum is the division of the mesencephalon ventral to the tectum. The tegmentum

contains three colorful structures that are of particular interest to biopsychologists: the

periaqueductal gray, the substantia nigra, and the red nucleus. 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 effects of opiate drugs. The

substantia nigra and red nucleus are both important components of the sensorimotor system.

Diencephalon

The Diencephalon is composed of two structures which are the thalamus and the hypothalamus.

The thalamus is the large, two-lobed structure that constitutes the top of the brain stem. Each

lobe sits on one side of the third ventricle and the two lobes are joined by massa intermedia

which runs through the ventricle. It is visible on the surface of the thalamus are white lamina

that are composed of myelinated axons. The thalamus comprises many different pair of nucleus

to protect the cortex. Sensory relay nuclei are a thalamic nuclei that receive signals from

sensory receptors, process them, and then transmit them to the appropriate areas of sensory

cortex. The hypothalamus plays an important role in the regulation of several motivated

behaviors. It exerts its efforts by releasing hormones through the pituitary gland.

Telencephalon

This is the largest part of the brain that mediates the brain’s most complex functions. It

initiates voluntary movement, interprets sensory input, and mediates complex cognitive

processes such as learning, speaking, and problem solving.

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