Neurotransmitters
Definition
Neurotransmitters are chemicals located and released in the brain to allow an impulse from one nerve cell to pass to another nerve cell.
Description
There are approximately 50 neurotransmitters identified. There are billions of nerve cells located in the brain, which do not directly touch each other. Nerve cells communicate messages by secreting neurotransmitters. Neurotransmitters can excite or inhibit neurons (nerve cells). Some common neurotransmitters are acetylcholine, norepinephrine, dopamine, serotonin and gamma aminobutyric acid (GABA). Acetylcholine and norepinephrine are excitatory neurotransmitters while dopamine, serotonin, and GABA are inhibitory. Each neurotransmitter can directly or indirectly influence neurons in a specific portion of the brain, thereby affecting behavior.
Mechanism of impulse transmission
A nerve impulse travels through a nerve in a long, slender cellular structure called an axon, and it eventually reaches a structure called the presynaptic membrane, which contains neurotransmitters to be released in a free space called the synaptic cleft. Freely flowing neurotransmitter molecules are picked up by receptors (structures that appear on cellular surfaces that pick up molecules that fit into them like a "lock and key") located
Once the neurotransmitter is released from the neurotransmitter vesicles of the presynaptic membrane, the normal movement of molecules should be directed to receptor sites located on the postsynaptic membrane. However, in certain disease states, the flow of the neurotransmitter is defective. For example, in depression, the flow of the inhibitory neurotransmitter serotonin is defective, and molecules flow back to their originating site (the presynaptic membrane) instead of to receptors on the postsynaptic membrane that will transmit the impulse to a nearby neuron.
The mechanism of action and localization of neurotransmitters in the brain has provided valuable information concerning the cause of many mental disorders, including clinical depression and chemical dependency, and in researching medications that allow normal flow and movement of neurotransmitter molecules.
Neurotransmitters, mental disorders, and medications
Schizophrenia
Impairment of dopamine-containing neurons in the brain is implicated in schizophrenia , a mental disease marked by disturbances in thinking and emotional reactions. Medications that block dopamine receptors in the brain, such as chlorpromazine and clozapine , have been used to alleviate the symptoms and help patients return to a normal social setting.
Depression
In depression, which afflicts about 3.5% of the population, there appears to be abnormal excess or inhibition of signals that control mood, thoughts, pain, and other sensations. Depression is treated with antidepressants that affect norepinephrine and serotonin in the brain. The antidepressants help correct the abnormal neurotransmitter activity. A newer drug, fluoxetine (Prozac), is a selective serotonin reuptake inhibitor (SSRI) that appears to establish the level of serotonin required to function at a normal level. As the name implies, the drug inhibits the re-uptake of serotonin neurotransmitter from synaptic gaps, thus increasing neurotransmitter action. In the brain, then, the increased serotonin activity alleviates depressive symptoms.
Alzheimer's disease
Alzheimer's disease , which affects an estimated four million Americans, is characterized by memory loss and the eventual inability for self-care. The disease seems to be caused by a loss of cells that secrete acetylcholine in the basal forebrain (region of brain that is the control center for sensory and associative information processing and motor activities). Some medications to alleviate the symptoms have been developed, but presently there is no known treatment for the disease.
Generalized anxiety disorder
People with generalized anxiety disorder (GAD) experience excessive worry that causes problems at work and in the maintenance of daily responsibilities. Evidence suggests that GAD involves several neurotransmitter systems in the brain, including norepinephrine and serotonin.
Attention-deficit/hyperactivity disorder
People affected by attention-deficit/hyperactivity disorder (ADHD) experience difficulties in the areas of attention, overactivity, impulse control, and distractibility. Research shows that dopamine and norepinephrine imbalances are strongly implicated in causing ADHD.
Others
Substantial research evidence also suggests a correlation of neurotransmitter imbalance with disorders such as borderline personality disorders , schizotypal personality disorder , avoidant personality disorder , social phobia , histrionic personality disorder , and somatization disorder .
Drug addictions
Cocaine and crack cocaine are psychostimulants that affect neurons containing dopamine in the areas of the brain known as the limbic and frontal cortex. When cocaine is used, it generates a feeling of confidence and power. However, when large amounts are taken, people "crash" and suffer from physical and emotional exhaustion as well as depression.
Opiates, such as heroin and morphine, appear to mimic naturally occurring peptide substances in the brain that act as neurotransmitters with opiate activity called endorphins. Natural endorphins of the brain act to kill pain, cause sensations of pleasure, and cause sleepiness. Endorphins released with extensive aerobic exercise, for example, are responsible for the "rush" that long-distance runners experience. It is believed that morphine and heroin combine with the endorphin receptors in the brain, resulting in reduced natural endorphin production. As a result, the drugs are needed to replace the naturally produced endorphins and addiction occurs. Attempts to counteract the effects of the drugs involve using medications that mimic them, such as nalorphine, naloxone, and naltrexone .
Alcohol is one of the depressant drugs in widest use, and is believed to cause its effects by interacting with the GABA receptor. Initially anxiety is controlled, but greater amounts reduce muscle control and delay reaction time due to impaired thinking.
Resources
BOOKS
Tasman, Allan, Kay Jerald, MD, Jeffrey A. Lieberman, MD, eds. Psychiatry. 1st ed. Philadelphia: W. B. Saunders Company, 1997.
Laith Farid Gulli, M.D.
Mary Finley
1. I was under the impression that for the neurotransmitters to jump from one nerve ending to another they required the synapse which is the area between the nerves and allows them to go across the gap between two nerve endings. But you say nothing about the synapse. I am a bit confused here, to say the least.
2. I was under the impression that when the neurotransmitters are blocked and cannot flow freely that many of the problems arise from this. After speaking with a number of Neurologists I have come to the conclusion that people who have this problem have a tendency to become either very angry and violent while others will become clinically depressed or close to it.
3. I have been told by many doctors that they don't know if the lack of neurotransmitters is the cause of the depression going outwardly or inwardly. They do know without a doubt that the introduction of electric shock treatment forces the neurotransmitters from being cooped up. They just have to be released in the face of the electric shock because that is how the brain works by sending information across the nerves from one to another?
Perhaps you will be able to explain to me what I cannot find out on my own. And outside of electric shock treatments are there any full proof method of releasing these almost immediately and/or not sharing that information with anybody.
Thank you much for your time and I will be awaiting your call concerning this matter.
I am Michael G. Murphy -- born in Renton, Washington on September 22, 1956, I was born and a trouble maker from the beginning nearly. However, I did get enough education to get a job and when she what I was doing she did drop me from this Pain is so severe during a lifetime.
God bless,
Michael