Brain Structuremyencephalonmesencephalonmetencephalondiencephalontelencephalonbrainanaotmysc

Anyone who has been fortunate to view an ultrasound image of an unborn child would be able to see the miracle of brain development unfolding. During the early stages of human life, a tube-like structure begins to appear within the tiny embryo, signaling the early stages of the central nervous system development. The following miraculous string of events may be unrecognizable to the untrained eye; however, they are the most significant moments of initial development in human life.

The tiny tube which is filled with fluid extends directionally from posterior toward the anterior region. It is on this anterior section that three areas begin to enlarge as they become the forebrain, midbrain and hindbrain. The three areas ultimately become five as the forebrain and the hindbrain areas further divide into two sections. These divisions in order from anterior to posterior are known as; telencephalon, diencephalon, mesencephalon, metencephalon and myelencehpalon. The word encephalon means, literally “within the head”(Pinel, 2007, p.50).

Beginning in the lowest division is the myelencephalon, also known as the medulla. The medulla has is a regulatory system for many bodily functions including numerous cardiac functions, and some respiratory reflexes (Pinel, 2007, p.52). The medulla is also a part of the brain stem, and operates as a highway for signals going to and from the brain. Inside the central core of the brain stem is a complex network of nuclei which ascends from the posterior to the anterior region and into the midbrain. The reticular formation often referred to as the reticular activating system (RAS) is said to be responsible for aroused states. Because there can be under or over aroused states, psychologists find the reticular activating system to be an especially important aspect in the study of learning disabilities and attention disorders such as ADD and ADHD (Cowan, (n.d), para.3).

Above the myelencephalon is the metencephalon, which is also a part of the brain stem. A bulge at the rear of the metencephalon is known as the cerebellum; part of its purpose is to control motor skills, therefore, any damage, disease or birth defect which affects it is likely to hinder movement (Pinel, 2007, p.53).

Catherine Limperopoulos, PhD and colleagues compared two groups of toddlers. All were born prematurely, but 31 had isolated cerebellar hemorrhage identified at birth, while 31 had normal brain imaging studies. In addition to motor problems, 61 percent of the children with cerebellar injuryversus just 3 percent of controlshad global developmental delays, including deficits in language, visual reception and social/behavioral function.

(Limperopoulos, 2005, para.3)

The mesencephalon, also a part of the brain stem, has two divisions, the tectum and the tegmentum. Within the tegmentum is the periaquaductal gray, or gray matter; a term familiar to most people, although many would not be aware of its origin. This gray matter is found around the cerebral aqueduct and “it is of special interest because of its role in mediating the analgesic (pain-reducing) effects of opiate drugs (e.g., morphine and heroin) “(Pinel, 2007, p.53). Damage to this area is highly possible for people who abuse drugs, and according to research conducted on rats, there could also be the risk of developing a tolerance to certain drugs such as morphine (Siuciak & Advoka, 1987, para.1).

The diencephalon is the uppermost part of the brainstem. It is located in the forebrain below the telencephalon, and is home to the thalamus and the hypothalamus. Part of the job of the hypothalamus is to control hormone excretion; these hormones come from the pituitary gland and as such, the hypothalamus plays a large role in certain behaviors. In close proximity to the pituitary gland is the area known as the optic chasm; the central meeting point for the nerves of both the left and right eyes (Pinel, 2007, p.54).

The telencephalon is the largest division of the brain; it sits on top of the brain stem above the diencephalon, in the forebrain. The telencephalon has a multitude of functions including learning and cognitive processes, interpreting sensory input, and controlling speech. The surface of the telencephalon has ridges called convolutions, which are seemingly in place so as to fit the large mass into its relevantly small area; the skull. The telencephalon is divided into two cerebral hemispheres which are joined by cerebral commissures; the largest of these commissures is called the corpus callosum. (Pinel, 2007, p.55).

Like other areas of the brain, any injury to the telencephalon has devastating consequences, and may even cause death. When an individual suffers a stroke, the cerebral hemispheres sustain damage, therefore the ability to speak can be severely impaired, or lost altogether. As an example, a stroke in the left hemisphere of the brain could not only cause the loss of speech, it may also cause the loss of senses in the right side of the body, paralysis in the right arm, leg or both. Additionally, a stroke often causes facial paralysis which also makes learning to speak extremely frustrating.

The brain is a miraculous creation, and as we evolve, scientists are discovering new and exciting information about how it functions. Testing continues on the newborn, the unborn, and in some cases, on animals. Every effort is being made to understand how the brain functions, although we may never be aware of its true capacity.


Psy.D, Cowan, D. (n.d.). What factors could cause the Reticular Activating System to be either over-activated or under-activated? Retrieved March 14, 2009, from New Ideas:

PhD., Limperopoulos. C. (n.d.). Cerebellar damage impairs cognition and behavior. Retrieved March 14, 2009, from Pediatric Views:

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

Siuciak JA, Advokat C. (1987). Tolerance to morphine microinjections in the periaqueductal gray (PAG) induces tolerance to systemic, but not intrathecal morphine. Retrieved March 14, 2009, from