Human Brain One of the most complex organs in the universe, the human brain, continues to be a scientific mystery. In vertebrate and most invertebrate animals, the brain is the central aspect of the nervous system. The brain can be simple, as in some insects, or extremely complex, as in the human brain which can encompass anywhere from 15-33 billion neurons linked with 10,000 or more synaptic connections. The brain is the control and interpretive mechanism for the senses -- vision, hearing, balance, taste, and smell. The brain also controls other body systems and organs with the release of chemicals allowing a more centralized, and often speedier, coordinated response to environmental stimuli. In vertebrates the spinal cord is the communication track that links the brain with the rest of the body. And, while scientific progress in many other areas of human physiology has been rapid over the past few decades, much is still unknown about the way the brain communicates, stores information, is descriptive with the release of certain chemicals, and certainly the way the brain ages and becomes diseased.

As mentioned, the brain is extremely complex, but many of the basic functions may be explained by definining the various regions of the brain, in this case the human brain. Basically, the brain consists of six major regions, with certain parts of the brain being subcategories of five macro areas. Depending on whether one is being structural or functional, descriptions of the brain may vary somewhat. The five macrocategories of the brain are:

The Myelencephalon -- the hindbrain or the secondary vesicle in the central nervous cyctem; the medulla oblaongata, the crainial nerves, and the most primitive (ancestral) part of the brain.

The Metencephalon -- also portions of the central nervous system; the pons and cerebellum; regulates the breathing center of the medulla oblongata, coordinates muscle movements, posture and integrates inner ear sensory information.

The Mesencephalon -- another ancient part of the brain, plays a role in motivation and habituation; the midbrain, tectum, tegmentum and cerebral peducles.

The Diencephalon -- the interbrain; thalamus, metathalamus, hypothalmus, prethalmus, pituaitary and pineal gland; regulates visceral activity and autonomic nervous system.

The Telencephalon -- forbrain; most superior region of the central nervous system; cerebral cortex, right and left hemispheres; all voluntary actions of the body.

The functional six categories of the brain are listed below. Some of the areas consist of folded tissue that allows more mass to exist within a smaller, more confined area (the skull). These major anatomical areas are the cerebral hemispheres (telencephalon), the htalamus and hypothalamus (diencephalon), the midbrain (mesencephalon), cerebellum, pons and medulla oblangata. These areas function as the major parts of the brain and are typically associated as:

Cerebral Hemispheres -- Essentially the right and left sides of the brain determined by the medial plane of the body. Each of these hemispheres has an outer layer of grey matter called the cerbral cortex, and an inner layer of ivory matter. The two sides of the hemispheres are linked by a large bundle of nerve fibers called the corpus callosum and others, which transfer information between the two hemispheres. Scholars believe that the differing hemispheres of the brain tend to focus upon differing behaviors in the normal adult brain. However, the brain is a marvelously robust organ, and seems to find new paths and ways of completing needed tasks by reassigning and reallocating cells to specific functions.

Thalamus and Hypothalamus -- A collection of neural nuclei with a number of diverse functions. The thalamus, for instance, helps relay information to and from the cerebral hemispheres. The hypothalamus is a smaller region at the base of the forebrain, is the central control for the sleep cycle, controls eating and drinking, hormone release, and is one of the clear biological bases of behavior.

Midbrain -- Also known as the mesencephalon, the midbrain contains the corporus...

It is more sophisticated than the inner, or reptillian brain, and, on the evolutionary scale allows for social behavior and the ability to adapt to the environment.
Cerebellum -- is a smaller area at the base of the human brain that plays a vital role in motor control, and is also involved in some cognitive functions like language and the regulation of fear and pleasure. It does not really initiate movement, but is necessary for fine motor skills, precision and accuracy. Anatomically, it looks like a separate structure, but is attached to the pons and contains a number of specialized cells that send output to even deeper nuclei that are located in the interior of the cerebellum.

Pons -- The pons is a structure located on the brain stem, upwards from the medulla oblongate and down from the midbrain, and in front of the cerebellum. Its white matter conducts signals from the berebrum into the cerebellum and medulla as well as sensory signals up into the thalmus. It is a stalk-like structure that relays signals dealing with sleep, respiration, bladder control, hearing, equalibrium, taste, facial sensations and expressions, and even posture.

Medulla Oblangata -- the medulla is the lower portion of the brainstem and contains the respiratory, cardia and autonomic centers (breathing, heart rate, and blood pressure). This portion is also known as the reptillian brain, in that, on he evolutionary scale, is functions on the basic systems to keep the organism alive.

Additionally, other areas of the brain that are anatomically important but are located within the hemispheric regions are:

Frontal Lobe -- The fronal lobe is an area of the brain in mammals located at the front portion of each cerebral hemisphere. It is part of cognitive maturity, and in humans, for instance, is not fully developed until the individual is in their 20s. It contains the most dopamine-sensitive neurons and is associated with long-term memory, planning, drive, judgment, and punishment/reward. The dopamine aspect tends to limit and control sensory information that comes from the thalamus into the fore-brain. Evolutionarily, this is the likely portion of the brain to develop last, since it involves the ability to judge and recognize future consequences that result from current actions, and to override and supress unacceptable social responses. For humans, these finer abilities at judgment were crucial to the development of community, culture and society.

Temportal Lobe -- The temporal lobe is a region of the ceebral cortex that is located on both the left and right sides of the brain. It is involved in auditory processing, the process of semantics, and contains another organ called the hippocampus, which plays a vital role in learning and long-term memory.

Occiptal Lobe -- this is the visual processing center of the mamillian brain. The area itself has a number of specialized tasks, even though it is the smallest of the four lobes. It has developed so that it can discriminate color and motion, as well as advanced spatial processing. In carnivores, it focuses on the ability to see and trek prey; while in humans, it allows subtleties of art, discrimination of multiple color patterns, and the ability to conceive advanced spatial structures.

Parietal Lobe -- This lobe is above the occipital and temporal lobe and integrates sensory information that helps differentiate spatial sense and the ability to navigate through the world. It helps the individual remember location and can "map" areas so the brain remembers where it has been. It has four anatomical boundaries, mostly fissures that fold inward. The Parietal lobe guides sensory information from various parts of the body, and in humans is responsible for the relationship of numerical data and how objects are manipulated.

Brain Stem -- The brain stem is the lower part of the brain that adjoins the spinal cord. It provides the main motor and sensory information for the face and neck via the cranial nerves. While a small organ, it is extermely important in that…