Neurons Neurotransmitters

Keywords action potential axon ion channel mechanoreceptor membrane potential neurons neurotransmitter olfaction proteins synaptic gap. 

University of Texas Addiction Science Research and Education Center. Understanding Addiction Basic Science Information. Available online. URL http //www.utexas.edu/research/asrec/addiction.html. Accessed May 28,2009. This Web page provides an abimdance of information on neurons, neurotransmitters—especially dopamine— and drugs that influence the transmission process. 

FIGURE 1—9- Neurotransmitter synthesis in a neuropeptidergic neuron. Neurotransmitter synthesis occurs only in the cell body because the complex machinery for neuropeptide synthesis is not transported into the axon terminal. Synthesis of a specific neuropeptide begins with the transcription of the pre-propeptide gene in the cell nucleus into primary RNA, which can be rearranged or edited to create different versions of RNA, known as alternative splice variants or pre-propeptide RNA. Next, RNA is translated into a pre-propeptide, which enters the endoplasmic reticulum, where its peptide tail is clipped off by an enzyme called a signal peptidase to form the propeptide, the direct precursor of the neuropeptide neurotransmitter. Finally, the propeptide enters synaptic vesicles, where it is converted into the neuropeptide itself. Synaptic vesicles loaded with neuropeptide neurotransmitters are transported down to the axon terminals, where there is no reuptake pump for neuropeptides. The action of peptides is terminated by catabolic peptidases, which cut the peptide neurotransmitter into inactive metabolites. 

Keywords Action potential Calcium Glia Ion channel LTP Neuron Neurotransmitter Potassium Resting membrane potential Sodium Structure Synapse... 

Keywords Activezone Central nervous system Dendrites Dendritic spine Neuron Neurotransmitter Peripheral nervous system Postsynaptic density Synapse... 

Dendrites are the (filamentous) terminal portions of neuron that bind neurotransrrritter chemicals migrating across the synaptic gaps separating neurons. Depending on the type and function of a particular neuron, neurotransmitters may cause or inhibit the transmission of neural impulses. The cell body contains the cell nucleus and a concentration of cellular organelles. The cell body is the site of the normal metabolic reactions that allow the cell to remain viable. Neurotransmitters synthesized within the cell body are transported to the axon terminus by microfilaments and microtubules. 

N voltage-gated neuronal neurotransmitter release conoioxin OVIA, MVIIC... 

Neurotransmitters are constantly being synthesized and stored in vesicles at the end of axons. The release of neurotransmitters into the synapse from vesicles in the presyn-aptic neurons results from the opening of calcium channels. Calcium fuses with the presynaptic neuronal vesicles, which brings about the release of the neurotransmitters into the synapse where they bind to receptors on postsynaptic neurons. Neurotransmitters control emotions and reasoning, affecting thoughts, feelings, dreams, memories, and actions. 

The chemistry of the brain and central nervous system is affected by a group of substances called neurotransmitters, substances that carry messages across a synapse from one neuron to another Several of these neurotransmitters arise from l tyrosine by structural modification and decarboxylation as outlined m Figure 27 5... 

The concept of discrete neurotransmitter recognition sites or receptors on nerve cells was based on work on systems physiology and dmg action (1). It was not until 1921 however, that it was shown that information could be transferred between neurons via a chemical, in this instance acetylcholine [51-84-3] (ACh), C H gN02 (1). 

The neurotransmitter must be present in presynaptic nerve terminals and the precursors and enzymes necessary for its synthesis must be present in the neuron. For example, ACh is stored in vesicles specifically in cholinergic nerve terminals. It is synthesized from choline and acetyl-coenzyme A (acetyl-CoA) by the enzyme, choline acetyltransferase. Choline is taken up by a high affinity transporter specific to cholinergic nerve terminals. Choline uptake appears to be the rate-limiting step in ACh synthesis, and is regulated to keep pace with demands for the neurotransmitter. Dopamine [51 -61-6] (2) is synthesized from tyrosine by tyrosine hydroxylase, which converts tyrosine to L-dopa (3,4-dihydroxy-L-phenylalanine) (3), and dopa decarboxylase, which converts L-dopa to dopamine. 

Stimulation of the neuron lea ding to electrical activation of the nerve terminal in a physiologically relevant manner should eUcit a calcium-dependent release of the neurotransmitter. Although release is dependent on extracellular calcium, intracellular calcium homeostasis may also modulate the process. Neurotransmitter release that is independent of extracellular calcium is usually artifactual, or in some cases may represent release from a non-neuronal sources such as gha (3). 

Serotoninergic neurons utilize serotonin [50-67-9] 5-hydroxy-tyrptamine (5-HT), as a neurotransmitter. Central serotoninergic... 

Acetylcholine is a neurotransmitter at the neuromuscular junction in autonomic ganglia and at postgangHonic parasympathetic nerve endings (see Neuroregulators). In the CNS, the motor-neuron collaterals to the Renshaw cells are cholinergic (43). In the rat brain, acetylcholine occurs in high concentrations in the interpeduncular and caudate nuclei (44). The LD q (subcutaneous) of the chloride in rats is 250 mg/kg. 

The chromaffin cells of the adrenal medulla may be considered to be modified sympathetic neurons that are able to synthesize E from NE by /V-methylation. In this case the amine is Hberated into the circulation, where it exerts effects similar to those of NE in addition, E exhibits effects different from those of NE, such as relaxation of lung muscle (hence its use in asthma). Small amounts of E are also found in the central nervous system, particularly in the brain stem where it may be involved in blood pressure regulation. DA, the precursor of NE, has biological activity in peripheral tissues such as the kidney, and serves as a neurotransmitter in several important pathways in the brain (1,2). 

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

Neurons have three parts the cell body and dendrites, the axon, and axon terminals. The cell body contains the nucleus and the organelles needed for metabolism, growth, and repair. The dendrites are branched extensions of the cell body membrane. The axon is a long, thin structure which transfers electrical impulses down to the terminals. The axon divides into numerous axon terminals and it is in this specialized region that neurotransmitters are released to transmit information from one neuron to its neighbors. The synapse has been defined as the space between two subsequent interrelated neurons. ... 

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