The Brain is one of the most amazing organs in the human body. It regulates and controls a number of different body functions, controls movement, helps us to experience sensation and emotion. In a journey through the brain starting from the top of the spinal cord and into the brain can give us a good idea into just what the brain is and what it does.
From the top of the spinal cord, one can see the brain clearly. The brain, is part of the Central Nervous System, one of the two nerve systems in the human body (the second system being the Peripheral Nervous System). The Central Nervous System consists of the brain and the spinal cord, as they are the main systems of nerve communication. Even the Peripheral Nervous System "reports" back to the spinal cord and then up to the brain.
The brain itself consists of three different parts: the Hindbrain, Midbrain, and Forebrain.
Thus, the first feature of the brain clearly visible from the top of the spinal cord is classified as part of the Hindbrain. In all actuality, the Medulla (the brain structure in question), is really an extension of the spinal cord up into the brain. This extension is partially just "white matter" in the brain, and partially clumps or neurons, or nuclei as they are called in the Central Nervous System. (Koenigshofer, 2004). The medulla serves to control basic life functions such as breathing, heart beat, blood pressure, and the like. Additionally, it relays important nerve information from the brain to the spinal cord. Since the Medulla serves such a basic, but important role in the brain and life, damage to this area can be, and usually is, fatal.
The next Hindbrain structure is the Pons, a protruding nodule-like part of the brain located forward with the next structure, the Cerebellum located on the backside of us and the Pons. The Pons serves as a regulator for breathing, while other nuclei in the Pons are rather famously known for their involvement in dream sleeping (or REM sleep). It is widely believed and accepted that the Pons contains nuclei that are trigger dream filled sleep.
Opposite the Pons is the Cerebellum, also part of the brainstem, as all Hindbrain and Midbrain structures are. Although the Cerebellum's role isn't exclusive, it does serve as a partial control for movement dealing with muscle coordination, body balance, and the formation and storage of muscle memory. As such, injuries to this area of the brain can cause severe problems with movement. As mentioned earlier, the Cerebellum shares movement responsibilities with another brain structure, so damage to the Cerebellum wouldn't cause paralysis. Instead, damage to the cerebellum would merely cause deficits in movement and certain deficit in muscle memory skills. Due to the Cerebellum's role in body equilibrium, a condition known as Ataxia can result due to Cerebellum damage. This condition is characterized by lack of balance, uncoordinated movements, and severe tremors of the body. (Romero, Kemp, 2007). With Ataxia, it becomes difficult to carry out even the simplest of actions such as waving or grabbing a pen.
The Midbrain structures come next in the line of structures visible as we work up from the top of the spinal cord in our exploration of the brain. The Midbrain is responsible for a great many of the visual and auditory functions of the brain including vision, eye movement, and hearing. The first structures we would happen upon in our journey through the midbrain would be the four bumps located on the backside of the upper brainstem. (Note that the brainstem is made up of both the Hindbrain and the Midbrain). These four bumps serve as controls and relays for eyes and ears; two for relays in the auditory system and two for the control of reflexes of the eyes. Without these bumps you wouldn't have the reactions to light you experience in the eyes, these are the sorts of reflexes that the Superior Colliculli control. The auditory relay bumps are called Inferior Colloculli.
Another important structure controlling eye movement in the Midbrain is a motor nerve called the Trochlear nerve. The Trochlear nerve is responsible for controlling the superior oblique muscle located next to the eye.
Before we leave the Midbrain, there is one other major structure that needs to be introduced. In fact, this structure is the structure that will lead us to the last and upper most section of the brain, the Forebrain. The Ascending Reticular Activating System or ARAS is located next to the Forebrain structure of the Thalamus, and is responsible for calling the Forebrain into action. In essence, the ARAS controls whether we are conscious, awake, and alert, drowsy and inactive, or even comatose. The ARAS plays a huge role in motivation to perform activities, sleep, and be alert do to the structure's actual level of activity. For example, if the ARAS is very active, we in correspondence with this, are also active, alert, and functioning at top level. In contrast, if the ARAS is very inactive, we can fall into a state of sleep. For this reason, damage to the ARAS causes victims to fall into a coma from which they cannot come out of without the healing of the ARAS. This structure, also known widely as the Reticular Formation, is essential for life as it signals the upper regions of the brain to respond to incoming sensory or action signals. Without an active ARAS we'd be walking around like zombies, or merely sleeping all day long.
The ARAS' counterpart, the Forebrain is the next part of the brain we move into and is involved in some of the most mysterious and complex duties of the entire brain. The Forebrain takes a front seat to behavioral and mental functions, and is thus still shrouded in a fair deal of mystery. Still, we do actually know a fair deal about the Forebrain and its structures, the first of which we happen upon is the Hypothalamus. The Hypothalamus has a great deal of responsibility within the brain. It's located at the base of the Forebrain, but is responsible for such things as body temperature regulation, emotions, hunger, thirst, and the autonomic nervous system; a system that controls fighting, fleeing, feeding, and sexual behavior. As you can see, the Hypothalamus has a great deal of responsibility. Any or all of these functions can be disrupted with damage to the Hypothalamus. In addition to these functions, the Hypothalamus also corresponds with the Pituitary gland.
The next Forebrain structure is the Thalamus, a structure located directly above the Hypothalamus. The Thalamus is responsible for processing sensory information and registering it to determine its properties. (Romero, Kemp, 2007). Once the Thalamus has determined its properties, it is able to send a message to the temporal lobe preparing the body for action it may want to take. The Thalamus plays a huge role in sensory perception and each of the senses has a nucleus in the Thalamus. Because the Thalamus plays such an integral role in sensory processing, injury to the Thalamus is too often fatal for the victim.
Next are several structures that are collectively called the Limbic System. The Limbic System consists of the Hippocampus, the Amygdala, Mammary bodies, and Cingulate Gyrus. These four structures regulate body temperature, blood pressure, and blood sugar levels. (Romero, Kemp, 2007). The Hippocampus is responsible for such things as learning and memory. If the Hippocampus is damaged on both sides of the brain, the victim becomes unable to store new information, nor call upon formerly stored information such as an address or a path to school. Additionally, this sort of damage causes an inability to remember short term events either.
The Amygdala is also responsible for learning and memory, but most specifically focuses on those memories with emotional aspects. The Amygdala plays the link between emotions and experiences and emotional expression. Without an Amygdala a person cannot register emotions properly, and thus cannot process threats and fears like typical people do. This may mean that a person may not sense a threat when a normal person would and thus will not react with aggression or alertness. The other parts of the Limbic System also serve emotions, the emotional response to situations, stimuli, and pain.
Next is the Basal Ganglia which is located near the Thalamus in the Forebrain, our current area of exploration. The Basal Ganglia is an important structure involved in the control of movement. It is damage to this structure that causes muscle movement disorders. Recently doctors have been able to make great advances in reducing or reversing the effects of Basal Ganglia damage. With drugs or neurological surgery muscle rigidity and difficulty moving can be treated.
While the brain still has a lot to discover, our journey through the brain is coming to an end as we examine the Cerebral Cortex and the Corpus Callosum. The Cerebral Cortex is located on the outermost area of the brain and is involved in thought, movement, language, perception, and reasoning. The Cerebral Cortex is divided in half and each half has four matching lobes. Each of these lobes contribute to conscious and even unconscious thought and emotion. The names of each of the lobes is the occipital lobe, the pariental lobe, the tempral lobe, and the frontal lobe. This part of the brain is actually responsible for such specifics as goal settings, planning, language production, visual information examination, body touch perception, auditory information, and storing visual information. (Romero, Kemp, 2007).
The Corpus Callosum is out last site on our journey through the brain. It's a thick band of nerve fibers that serve as a communication point between the right and left side of the brain. Without the Corpus Callosum the two halves work independently and can only process specific information.
We have journeyed a long way through a very complex structure called the human brain. We've seen and experienced the duties carried out by the base of the brain known as the Medulla, and traveled through the Hindbrain and Mibrain structures to study the most complex and mysterious part of the brain, the Forebrain. While mystery still surrounds the brain and its various functions, we have been able to discover the basic functions and processes it undergoes to make our bodies move, experience emotions, feel sensations, and store visual information. It is because of these complex processes and functions that the brain is such an amazing body organ.
Koenigshofer, K. (2004). Biological Foundations of Mind and Behavior. UMUC Web Tycho Lecture.
Chudler, E. (2006). Divisions of the Nervous System. Retrieved April 18, 2007, from Neuroscience for Kids Website: http://faculty.washington.edu/chudler/nsdivide.html
Romero, A. PhD., Kemp, S. PhD. Psychology Demystified. McGraw Hill Publishers. New York, NY.
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