Monday, September 28, 2015

Neurochemistry

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Neurochemistry
Multiple Responses:
1.
Neurochemistry is the specific study of neurochemicals, including neurotransmitters and other molecules (such as psychopharmaceuticals, neuropeptides, or gastrotransmitters) that influence the function of neurons. This field closely examines how these neurochemicals influence the network of neural operation. This evolving area of neuroscience offers a neurochemist a micro-macro connection between the analysis of organic compounds active in the nervous system and neural processes such as cortical plasticity,neurogenesis and neural differentiation.

2.
Brain chemistry or neurochemistry is the complex system which allows the brain to function with the use of chemicals known as neurotransmitters which move information around in the brain. Every person's brain chemistry is slightly different, and a number of things can play a role in the levels of various neurotransmitters in the brain, and how those chemicals affect the brain's function. It is believed that variations in brain chemistry may explain a variety of behavioral disorders and phenomena.

The brain is a network of specialized cells called neurons. Each neuron has reserves of neurotransmitters which it can fire when ordered to so, along with receptors for specific neurotransmitters. Brain activity is created by sending messages with neurotransmitters to signal various cell activities throughout the brain and nervous system.

Someone's environment can influence the levels of neurotransmitters and their receptors in the brain, as can factors like diet, medications, and various drugs. Some chemical compounds appear to have long term effects. Nicotine, for example, is heavily involved with the neurotransmitter dopamine. These external influences on chemistry in the brain can cause behavioral changes or alterations in the way the brain functions; people who smoke, for example, form an addition tocigarettes as a result of the way in which nicotine changes brain chemistry.

Some people also appear to be prone to alterations in their brain chemistry which can occur as the result of genetic or internal functions. Depression, mania, and many other psychiatric disorders are closely linked with the chemistry of the brain, which means that specific medications can often be used to adjust a patient's chemistry to help him or her achieve more normal brain function. These medications act differently on different people because the chemistry of the brain is very complex and varied, making it difficult to formulate a one size fits all medication to treat conditions like depression.

Certain personality types have also been linked with the levels of various neurotransmitters and receptors in the brain. Risk takers, for example, often have fewer dopamine receptors in their brains, which can mean that they have to work harder for a sense of satisfaction and reward. This may push them to engage in risky behaviors.

Changes in brain chemistry do not just affect mood. They can also have a larger impact on the nervous system, which means that people can develop conditions such as tremors and neuralgia as a result of an alteration to the fundamental chemistry of the brain.

3.
WHAT EXACTLY IS NEUROCHEMISTRY?
Neurochemistry is the specfic study of neurochemicals including neurotransmitters and other molecules (such as psychopharmaceuticals) that influence the function of neurons. This field closely examines how these neurochemicals influence the network of neural operation. Or in simpler words brain chemistry (neurochemistry) is the complex system which allows the brain to function with the use of chemicals known as neurotransmitters which move information around in the brain. Every person's brain chemistry is a little bit different, and a number of things can play a role in the levels of various neurotransmitters in the brain, and how those chemicals affect the brain's function. It is believed that variations in brain chemistry may explain a variety of behavioral disorders and phenomena. The brain is a network of specialized cells called neurons. Each neuron has reserves of neurotransmitters which it can fire when ordered to do so, along with receptors for specific neurotransmitters. Brain activity is created by sending messages with neurotransmitters to signal various cell activities throughout the brain and nervous system. Someone's environment can influence the levels of neurotransmitters and their receptors in the brain, as can factors like diet, medications, and various drugs. Some chemical compounds appear to have long term affects. Nicotine, for example, is heavily involved with neurotransmitter dopamine. These external influences on brain chemistry can cause behavioral changes or alterations in the way the brain functions; people who smoke, for example, form an addiction to cigarettes as a result of the way in which nicotine changes brain chemistry. This project is going to be discussing the different major types of drugs and how they affect the brain.

4.
NEUROCHEMISTRY
None of the billions of nerve cells, or neurons, in the human brain functions alone. To process information, neurons must form circuits and must communicate with each other rapidly and with great precision. Within a neuron, the electrical impulses that carry information are propagated by rapid changes in membrane potential that arise from the controlled opening and closing of ion channels. These pores in the cell membrane permit the controlled passage of positive or negative ions between the interior and exterior of the cell, and thereby the conduction of electrical impulses along the cell's processes. Additional mechanisms are required at synapses (neuron junctions) to pass signals from one neuron to another. Although a few neurons form electrical synapses, where electrical signals are conducted directly from one neuron to the other through specialized ion channels (gap junctions), most neurons in the mature nervous system communicate via chemical synapses. At chemical synapses, electrical activity in a presynaptic neuron causes the release of a chemical messenger, a neurotransmitter,which diffuses across the narrow synaptic cleft to bind to neurotransmitter receptors on the postsynaptic neuron and elicit changes in the electrical activity of that neuron.

Neurochemistry of synaptic transmission
Multiple neurochemical processes are involved in the synthesis, packaging, and release of neurotransmitters, and in the production and function of neurotransmitter receptors. Significantly, each of these biochemical steps represents a point of potential regulation of synaptic function and a site of possible age-related changes.

Most neurons produce and release one of several small molecules that serve as neurotransmitters, including acetylcholine, biogenic amines (dopamine, norepinephrine, epinephrine, histamine, or serotonin), or amino acids (glutamate, glycine, or gamma-aminobutyric acid). Many neurons also release one or more neuroactive peptides (neuropeptides), which provide additional modulation of signal transmission. Low levels of neuronal activity often result in release of only the small-molecule transmitter, whereas higher levels of activity result in the co-release of neuropeptides. Release of the neuropeptides may cease at very high levels of activity, however, since peptides must be delivered from the cell body and are replenished slowly. In contrast, synthesis and packaging of other neurotransmitters occurs more rapidly because the necessary synthetic enzymes are present within the cytoplasm in the region of the synapse. The release of neurotransmitters depends upon an increase in intracellular calcium that occurs with the depolarization (decrease in membrane potential) associated with the arrival of action potentials, regenerative waves of electrical activity that are the basis for signaling along neronal processes. Increased calcium leads to modification of vesicle-binding proteins, which facilitate the fusion of vesicles, membrane-bound packages in the cytoplasm, with the cell membrane and subsequent release of the vesicles' contents into the extracellular space.

After release, all neurotransmitters bind to neurotransmitter receptors and initiate changes in the postsynaptic neuron. It is the biochemical properties of the receptor protein, rather than that of the neurotransmitter itself, that determine the response of the postsynaptic cell. Each neurotransmitter binds to a different receptor, although multiple receptor types exist for several neurotransmitters, with each receptor initiating a different response in the target neuron. Functionally, neurotransmitter receptors fall into two groups, based on the mechanisms by which they alter the electrical activity of a neuron. Ionotropic receptors include an ion channel as part of their structure, and binding of the neurotransmitter results in immediate opening of that ion channel. Metabotropic receptors influence ion channels indirectly through activation of one of several second-messenger pathways. The three second-messenger systems that have been identified so far are similarly organized in that each includes a ligand-binding receptor domain coupled to a transducer that regulates the activity of an effector enzyme. The enzyme produces a second messenger that acts directly on one or more target proteins or activates additional, secondary effector enzymes. In addition to regulating ion channels, second-messenger systems may influence a variety of intracellular processes and elicit long-lasting changes in stimulated neurons.

Once a neurotransmitter has activated its receptors, it must be removed or destroyed rapidly in order to permit transmission of subsequent signals. Some neurotransmitters, regardless of type, simply diffuse from the synaptic cleft. Small-molecule neurotransmitters are also taken back up by presynaptic and postsynaptic neurons and by neighboring cells. One neurotransmitter, acetylcholine (ACh), is broken down rapidly by a membrane-bound enzyme in the region of the synapse. Neuroactive peptides are eliminated only by diffusion from the synaptic cleft and by proteolysis (degradation) by extracellular enzymes; thus they tend to have more sustained effects than small-molecule neurotransmitters.

Effects of age on the neurochemistry of synapses
Normal aging appears to result in significant but restricted neurochemical changes in synapses. Each of the many steps involved in neurotransmission may be altered in some neurons, but it does not appear that there are global changes in the neurochemistry of all synapses. Studies of neurotransmitter synthesis are difficult because most of the synthetic enzymes are unstable and difficult to measure; however, synthesis of ACh has been demonstrated to diminish with age in some brain regions, including the cerebral cortex. Levels of other neurotransmitters (e.g., dopamine) also appear to decline late in life, also in a regionally specific manner. Age-related changes in neurotransmitter receptors have been studied by direct assay of the proteins and by analysis of the binding of labeled neurotransmitters to sections of the brain. Receptors for the neuropeptides and for some amino acid neurotransmitters appear to be relatively resistant to age-related changes. In contrast, ACh, dopamine, and serotonin receptors decline with age in several regions of the brain. Even for synapses at which both neurotransmitter levels and neurotransmitter receptors are maintained, changes in second-messenger systems may produce age-related declines in synaptic function. Such changes may account for an age-dependent loss of plasticity —that is, a decline in the ability of synaptic stimulation to produce the sustained biochemical changes in postsynaptic neurons that underlie learning and memory.

Functional consequences of age-related neurochemical changes

It is difficult to link age-related changes in the neurochemistry of synapses to specific changes in cognitive function. Neurochemical studies of experimental animals are easier to perform and better controlled than those using postmortem human brain tissue, but they are not readily related to cognitive changes in humans. Despite such difficulties, however, there is accumulating evidence that age-related declines in transmission at cholinergic, serotonergic, and dopaminergic synapses contribute to changes in motor function, mood, and memory, respectively. Recent developments in functional brain imaging have provided significant advances in studies of the neurochemistry of synapses, changes in the aging brain, and their relationship to cognitive function. Radioactive ligands for specific neurotransmitter receptors, which can be imaged in living subjects using positron emission tomography (PET), permit investigators to visualize the activity of specific types of synapses in discrete regions of the brain. This approach permits direct comparisons of synaptic function in the brains of individuals of different ages and allows investigators to link neurochemical differences to differences in cognitive function.

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