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The nervous system is a complex network of specialized cells throughout the human body. The core of the nervous system is your brain, which controls all functions necessary for you to survive. The nervous system contains special cells, or neurons, that communicate among themselves. Your brain has approximately 100 billion neurons. Neurons have organelles just like regular cells- a nucleus, cytoplasm, and mitochondria. They relay messages using an electrochemical process, and require special structures not found in most cells. Examples of these structures are extensions called dendrites and axons. Neurons use axons and dendrites to transmit messages to each other. The main difference between these two is that axons send information out of the cell, but dendrites bring data in. Aside from that, there is generally only one axon per cell, axons have no ribosome, and they branch away from the cell body (soma). There are usually many dendrites per cell, dendrites have ribosome, and they branch closer around the soma. Axons and dendrites use chemicals that travel between neurons to communicate. These chemicals are called neurotransmitters.
In 1920 an Austrian scientist named Otto Loewi discovered the neurotransmitter. The concept came to him in a dream, and he tested his hypothesis using two frog hearts. Heart A was still attached to the vagus nerve, and was put in a chamber full of saline. The chamber was connected to another chamber containing Heart B. The chamber with Heart A was slightly higher than the chamber with Heart B, so fluid was allowed to flow from Chamber A to Chamber B. Otto electrically stimulated the vagus nerve, causing Heart A to slow down. After a short pause, Heart B slowed down also. Loewi used this experiment to hypothesize that electrical stimulation of Heart A caused a chemical to be released, which slowed down the heart. This chemical traveled from Chamber A to Chamber B, which caused Heart B to slow also. Loewi termed the chemical Vagusstoff, which is now known as the neurotransmitter acetylcholine.
Neurons may be classified by the number of protrusions that extend from their body. Bipolar neurons have two processes extending from their soma. Pseudounipolar cells have an axon that points toward the spine, and another axon protruding toward skin or muscle. Multipolar neurons have many processes extending from their body, but only one is an axon.
As stated earlier, neurons communicate electrochemically. This means they use electricity and chemicals to transmit data. Neurons are separated by a gap, or synapse. A synapse is composed different parts. The presynaptic ending has neurotransmitters and organelles. The postsynaptic ending has receptors for neurotransmitters. The synaptic cleft is the open space between the presynaptic and postsynaptic endings. When a neuron initializes communication, it sends an electric impulse down the axon to the synaptic terminal. This spike triggers vesicles containing neurotransmitters to travel toward the presynaptic membrane. When they reach the synaptic membrane, the vesicle membrane fuses, forcing the neurotransmitters out into the synaptic cleft. A recent discovery showed that neurons could release different types of neurotransmitters. The neurotransmitters diffuse across the gap and bind with receptor sites on the opposite side, the postsynaptic ending. The receptors provoke an electrical response in the receiving neuron. The reaction changes the postsynaptic cellís "excitability." This makes it more or less likely to fire an action potential, or electrical impulse. Enough signals will add together to make the neuron fire.
New technology has been developed that enables us to see inside the brain. Now we can understand the specific functions of parts of the brain and their relationship with other parts. We can identify different neurotransmitters and discover their purpose in the brain. We can also find parts of the brain that have neurological disorders and develop new ways to treat these ailments.
The CT Scan (Computed Tomography Scan) uses x-ray beams that pass through your head to create images that are developed into sensitive film. This method shows the structure of the brain, not its function.
The PET (Positron Emission Tomography) detects radioactive material that is inhaled to produce an image of the brain. The radioactive material goes to the bloodstream and when it is broken down, it gives off neutrons and positrons. When the positron hits an electron, two gamma rays are released. The gamma ray detectors record the brain area where the gamma rays came from. PET is a method that shows a functional view of the brain. Its advantage is that it shows images of brain activity, although it is quite expensive and radioactive material is used.
MRI (Magnetic Resonance Imaging) has no x-ray or radioactive material. It shows a detailed three-dimensional view of various structures inside the body, and is safe and painless. MRI is very useful for examining the soft tissues of the body, particularly the spinal chord or brain, without the risks involved of opening up a patient. MRI uses a very powerful magnet to align the nuclei of a bodyís atoms to one direction. A momentary pulse is aimed at the body, causing the atoms to spin and release a tiny radio signal. Each body tissue has a unique signal. These signals are converted into an image for viewing. A MRI is usually very expensive and is not used on uncooperative patients, but it safely maps the brain without exposing the patient to dangerous radiation.
FMRI (Functional Magnetic Resonance Imaging) detects changes in the blood flow to areas of the brain.
Neuroscientists have many other methods with which to study the brain. Behavioral neuroscience techniques are used to study the neural basis of behavior. Stereotaxic surgery uses a brain atlas to show different locations of the brain. It is used to put recording or stimulating electrodes or to destroy a specific part of the brain. Electrical brain stimulation stimulates part of the brain to pass an electric current through an electrode. Microinjection is when they inject small quantities of drug or neurotransmitters into a particular part of the brain.
Neuroanatomy techniques are used to study the structure of the nervous system. There are also many methods in neuroanatomy. Cell body staining is the coloring of neurons to enable you to see each individual neuron or groups of neurons. Tract tracing is the tracing of projections from different parts of the nervous system. This can work backward or forward. Electron microscopy lets electrons pass through tissue to produce more detailed images. Immunocytochemistry finds particular chemicals, such as neurotransmitters and proteins, in specific neurons. Deoxyglucose uptake is a method in which active neurons use glucose. Inject deoxyglucose into cells that use glucose, and they take up the deoxyglucose. It is not degraded so it stays inside the neuron. Scientists use a radioactive label on deoxyglucose so they can find out what areas of the brain are active at specific times.
Neurophysiology techniques are used to better understand the function of oneís nervous system. The Patch clamp technique records the current flow from single ion channels of a neuron. Intracellular recording is the electric recording inside a neuron. Extracellular recording is the electric recording outside a neuron. Mass unit recording is the electric recording from outside a group of neurons.
There are many more methods with which we can study and learn more about the brain. All of these techniques have a distinct purpose. Scientists are still finding more of them so we can heal people who have brain disorders and find which parts of the brain are useful in our everyday lifestyles. With more knowledge of the brain and how it works, we improve the chances of successful brain operations.
Several operations and experiments have been conducted towards brain research. Aristotle had his opinion; he thought the center for thought lied in the heart and the brain was used to help cool down the body. One laughs at this now, knowing better, but scientists still know relatively little about the three-pound mass of gray matter in our heads. However, using modernistic neuroscience methods, researchers have greatly refined our view of the brain and invented practical ways to cure disorders.
At age six Matthew Simpson was experiencing continuous seizures (electrical misfiring that impedes the brain), sometimes one every three minutes. Matt's parents brought him to Ben Carson, a pediatric neurosurgeon at Johns Hopkins Hospital. Carson suggested a hemispherectomy, an operation done to remove the left side of the brain. This would make Matt lose half of his cortex, the part one's mind that handles the thought process and ultimately makes one a human. After removal the empty part of the skull would fill up with cerebrospinal fluid at a rate of one teaspoon every five minutes. Delicate operations like this usually result in crippling, coma, death, or occasionally recovery.
In the 1940's, hemispherectomies were extremely fatal, yielding a small percentage of surviving patients. But since the mid 1980's pediatric neurosurgeons have revitalized the procedure by combating the excessive bleeding.
Now many hemispherectomies are performed as treatment for Rasmussen's encephalitis, which is a type of inflammation of the brain, and other forms of epilepsy that damage the cortex but do not cross the separating groove of the left and right hemisphere. Patients survive these operations because neither the disease nor the operation touches the cerebellum, which coordinates movement; the dencephalon, which facilitates emotions and regulates body functions; and the brain stem, which maintains breathing, heart rate, and other life-supporting systems.
The surgery proceeded successfully. Matt's seizures stopped, and the operation left only a scar and a slight limp. Matt has limited use of his right arm, and retains no peripheral vision in either eye.
A similar case to Matt's was Jody Miller, a three year old little girl who suffered seizures every few minutes as a result of Rasmussen's encephalitis. Jody could not stay up; she would topple over if not constantly held by her father. She had also lost the use of her left arm and leg.
Doctors at Johns Hopkins Hospital suggested removing the diseased right side of her brain. Jody's parents had no choice but to have her endure a hemispherectomy. The doctors cut open Jody's scalp, skull, and dura (the leathery covering of the brain). The doctors removed the diseased tissues leaving a cavity in Jody's skull, which was filled with cerebrospinal fluid.
After the eleven-hour operation, Jody was completely free of seizures. Neurons in the left hemisphere made multitudes of new connections, taking over some of the functions of the right hemisphere. Therapy has helped, but cannot restore full movement to her left side. "She's a bright, lovely young lady who doesn't use her arm very well," said Dr. Freeman.
Brain diseases have been researched and experimented for years. Strokes, Alzheimer's disease, and schizophrenia are some mysteries that still remain unsolved.
Strokes occur quickly. 80% of the time they are caused by fat plugs and blood clots in a brain artery, cutting off blood flow. This lack of blood means no oxygen or glucose can get to the brain, and waste cannot be removed. Cells around the artery and those supplied by it die off. The fat plugs and clots occur in neck arteries or even the heart. Other effects of the clogging are high blood pressure, abnormalities in blood vessels, and bleeding in the brain.
The cells die rapidly in the umbra. Around that is the penumbra, where cells die more slowly. Scientists and doctors have been trying to find a way to save the cells in the penumbra. Maybe in future medical advances this problem will be solved.
In a patient with Alzheimer's disease, the neurons die, and the brain shrivels, causing neural connections to wither. Small, abnormal filaments are formed inside neurons that choke healthy cells. Between neurons, the beta amyloid protein clumps with glial cells and misshapen nerve endings, forming feeble plaques. These tangles and plaques usually occur in the hippocampus, which is the part of the brain that facilitates memory formation, and the cortex, which controls reasoning, judgement, language, and orientation. Factors such as aging, genes, and environment work together to cause plaques and tangles. Research has been done to prevent these elements. Maybe in the near future the answer to plaques and tangles will be found.
We believe that the study of the brain is very important to the human race. New discoveries concerning the brain are made every day. These new techniques enable us to save lives in ways not possible before. For instance, eight-year-old Matthew Simpson, who was suffering from profuse seizures, was restored to stability by new methods of hemispherectomies. Now scientists can treat other children with brain disabilities, such as Jody Miller. They are now using these studies to find new cures for Alzheimerís disease, schizophrenia, and Parkinsonís disease. They are even researching new ways to repair damage caused by strokes and other brain impairments. With the new information, scientists are on the way to curing psychological predicaments such as abnormal aggression and manic depression. Scientists have used serotonin to treat a variety of central nervous system disorders, such anxiety, depression, schizophrenia, and hypertension. These facts support our belief that neuroscience is a vital component to the quest for human knowledge.
One reason we must discover more information about our mind is that we must learn to use it to its greatest capacity. Cicero said, "What we do not understand we do not possess." When we master the brain, we have acquired the ability to stretch its limits and use it to its fullest extent. With more knowledge of the brain and its structures, we can improve its performance and broaden our comprehension of how the three-pound lump of gray mass in our skull operates.
We are convinced that there are ways to improve the results acquired from brain research. Scientists have been using dopamine-producing cells from human fetuses to aid victims of Parkinsonís disease. For one patient, up to fifteen fetuses must be "harvested" to produce enough cells to help the patient. Even then, this process does not always work. We have no doubt that an alternative method could be discovered. This would save the lives of countless innocent babies. If scientists can find a way to remove half of a brain, we know they could find a new way to cure Parkinsonís disease and spare innocent lives.
As these instances portray, neurology is a vital factor in improving our society. When we have grasped the complexity of the organ that makes us who we are, we have obtained it, and therefore mastered it. We can then expand our mind to its greatest dimensions.