Is it our actions, our sense of purpose, or our ability to keep our mind on as well as perform complex tasks? Is it that we analyze our own mental processes, as well as the processes of others? What exactly is a mental state, and what creates it? Is it a level of attentiveness, an impulse, or an emotional state? What is it that allows us to experience these things? The answers all lie within our brains. The brain, like the rest of the nervous system, is composed by and large of neuralgia (glial cells), nerve cells (neurons), that are immersed in a constant flow of cerebrospinal fluid.
The glial cells far outnumber the neurons, but have no axons or synapses, and therefore do not play a part in the electrical activity of the brain. They are simpler looking, much smaller, and have lower metabolic rates than neurons. Another important difference includes that glial cells maintain the ability to recover from an injury and divide their entire lives. Virchow first identified these cells in 1846, and gave them the name neurogila, which means nerve glue. Glial cells are credited with holding the brain together, and preserving its physical structure.
They are also said to provide both chemical and electric insulation for synapses, as well as the other components of the brain, and transportation for chemicals between neurons and capillaries. Finally, glial cells are thought to break down and/or synthesize the neurotransmitters released by the neurons they shelter. Many mental illnesses are mainly caused by disorders relating to the metabolism of neurotransmitters. Neurons are the cells that create brain activity, passing chemical and electric signals from one to another.
Neurons come in a vast variety of shapes and sizes, but all have branches that fall into one of two categories: dendrites (receptors) and axons (transmitters). Neurons intercommunicate through a synaptic cleft, which is the minuscule gap where an axon from one cell transmits impulses, by the use of neurotransmitters, to the dendrite or cell surface of another neuron. These synapses fall into the three categories, which include excitatory, inhibitory, and modulatory. A healthy human is born with about ten thousand million neurons.
These neurons will be connected with up to ten thousand other neurons; receiving rapid pulses from a connected cells axon through its own dendrite will activate a cell. When the cell is stimulated, its axon will conduct signals away from the cell using neurotransmitters, and creating a chain reaction. The signal a neuron transmits can be altered slightly, because the cell has the ability to respond to stimuli at strengths different than how it was received. Additionally, the effects of a neurotransmitter is dependant on what type of neuron and dendrite it comes into contact with, as opposed to merely following its normal chemical nature.
For this reason, it is hypothesized that there are different transmitters for each kind of receptor. Neurotransmitters are messengers, forwarding impulses from cell to cell, using its axon, and chemicals to stimulate another neurons dendrite. Over fifty different neurotransmitters have been isolated and identified. The chemicals are contained in little sacs, called synaptic vesicles, located at the end of each neuron. The compounds that are considered to be most important are serotonin, noradrenaline, and dopamine. In 1988, Eli Lillys discovery, the drug fluoxetine, started to be prescribed under the commercial name, Prozac.
As a selective serotonin reuptake inhibitor, it enhances serotonin levels by plugging up the nerve cells that absorb the chemical, preventing it from exiting the brain. A large percentage of the population found it effective in raising mood levels and lowering anxiety, creating a feeling of tranquility and optimism. For these reasons, serotonin is dubbed the feel-good neurotransmitter. It works as an inhibitor, and brings the feelings of relaxation by constricting blood vessels – an act which also gives serotonin the ability to regulate temperature.
One interesting set of drugs called agonists, trick receptors into thinking they just received a neurotransmitter stimulation. They are selective, only stimulating specific receptors, and can unclog a blocked receptor with its stimulation abilities. The chemical serotonin, like other transmitters, has several different receptor types, which are 5HT-1, 5HT-2, and 5HT-3. One that has received a lot of attention is the 5-HT2 receptor, as it is one of the receptors that cause addiction on a chemical level. The serotonin 5-HT2 receptor is what is activated when a person does or uses something is addictive.
Some examples are the illegal drugs LSD and cocaine, and the diet drugs PhenFen and Fenfluramine (which were banned). It can also be activated when a person overeats or indulges their sweet tooth and feels satisfied. An addiction develops when the body learns to crave the stimulation of these receptors, and the person learns to crave whatever it is that causes their receptors to be activated. It is believed that some people overeat because they crave the sensation of the serotonin 5-HT2 receptors being activated, and eating provides the stimulus needed for activation by increasing the amount of Triptophan and sugar in the blood.
The diet drug PhenFen was taken off the market when it proved to be not only habit forming, but also hazardous to the health. What is does is trick the serotonin 5-HT2 receptors into acting as though a large meal has just been eaten. If these receptors get clogged, the brain and body have the opposite reaction. A person can eat a huge meal full of sugar, and still not feel satisfied. Serotonin is also responsible for information processing. It guides our attention to something by analyzing what information is important, and giving it priority by guiding our attention away from other stimuli.
A lack of serotonin will impair directed attention, or concentration. It is also a key chemical factor in hypotension, vasomotor contractions and responses, sexual behavior, and sleep. The noradrenaline neurotransmitter acts as an excitatory transmitter (excites and inhibits neurons), and shows an uneven regional distribution because it occurs mainly in the lower sections of the brain. One function of this transmitter is that it controls glucogenolysis, by sending signals to the liver telling it to convert sugar into glucose, putting it in the blood stream, and creating energy for the individual.
The chemical also creates energy for the body by controlling the conversion of fatty acids from the blood into energy for the body. Noradrenaline, like all other neurotransmitters, can be clogged up by substances such as antagonist drugs, manmade chemicals, some natural toxins, and heavy metal molecules. Unlike serotonin agonists, noradrenaline agonists are not addictive, and are therefore safe to use to help clear up transmitter blockages.
The neurons respond to this form of stimulation by reducing weariness, by delivering more biochemical energy to the body in the form of increased glucose in the blood, and increasing the level of oxygen in the cells. Dopamine is a neurotransmitter that controls arousal in many parts of the brain. It is dispersed throughout the brain via distinct pathways, particularly to the prefrontal cortex, which it activates. It is responsible for motor behaviors, as well as inhibiting the peptide prolactin, a chemical that is responsible for intense stress.
Dopamine also important for the protection of the cognitive sets that produce logical thought, and the ability to perform purposeful tasks, and the ability to concentrate and screen out nonmeaningful stimulus. Having unusual dopamine levels is considered a key factor in disorders like Parkinsons disease, and schizophrenia. In Parkinsons disease, levels of the chemical get so low, voluntary movement becomes impossible. A low level of dopamine in the basal ganglia frontal lobe and the ventral tegmental nucleus pathway is a factor in negative symptom schizophrenia where the affected person becomes introverted and apathetic.
On the other end of the scale, excessive levels of the chemical can cause positive symptom schizophrenia. In this situation, an affected person may have hallucinations and become excessively paranoid. Not every neurotransmitter has been found, and we are far from identifying what they all do, and how they all work. To understand ourselves, we must understand the brain. Every day new discoveries are made, explaining why we feel so satisfied after a big pancake breakfast, or how we can be so immersed in a book that we dont feel a tap on the shoulder. The future, and more research, holds the keys to many more of the mysteries locked within us.
