1. Transmitters - 1 of 8 Transmitter systems of the central...

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1 of 8 Transmitter systems of the central nervous system Dr. C.S. Leonard I. Goals A. An overview of the intercellular signaling modes utilized by the CNS. B. To review the most prevalent intercellular signaling mechanisms utilized by the CNS. C. To understand the distribution patterns and connectivity of major identified chemical transmitter systems in the CNS. D. To understand the actions of some identified transmitter systems in the CNS. I. Modes of intercellular signaling in the CNS. A. The most prevalent form of neuronal communication in the brain occurs via chemical synaptic transmission. This is mediated by a large number of chemicals that have been identified as transmitters and by the even larger number of receptors that function as receivers.
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2 of 8 B. What criteria must be met for a substance to be considered a neurotransmitter? Synthesized and packaged into vesicles in terminals Released from terminals in Ca dependent manner. Receptors for substance near release sites Mechanism for termination of action (enzyme breakdown or uptake via transporters) C. Numerous small molecules have been identified as likely neurotransmitters in the CNS. They are: Glutamate (Glu), ! -amino-butyric acid (GABA), Glycine (Gly), Serotonin (5-HT), Norepinephrine (NE); epinephrine (E), dopamine (DA), acetylcholine (Ach), Histamine (His) and the purines: Adenosine (A) and Adenosine-Triphosphate (ATP). In addition, numerous peptides appear to be transmitters as well. These include: Substance-P, Vasopressin, Oxytosin, Bombasin, Vasoactive Intestinal Peptide (VIP), endorphins and enkephalins. II. The actions of neurotransmitters are mediated by Ionotropic and Metabotropic receptors It is now clear that cellular effects of particular transmitters are determined by the particular receptors that bind them. The release of a transmitter can result in drastically different effects depending on which receptor subtypes are present at the target and their particular effectors. A. Ionotropic receptors are receptors containing an intrinsic ion channels. They are termed ligand-gated ion channels. In the brain, ionotropic receptors have been identified for numerous small molecules transmitters: Glutamate, GABA, Glycine, 5-HT, Ach and ATP. Each of these molecules have at least one type of ionotropic receptors. Some, like Glu and Ach have many types of ionotropic receptors. Signals mediated by ionotropic receptors are fast. The rapid and specific point -to- point computations performed by neurons in the CNS rely on fast- ionotropic signaling systems. The archetypical ionotropic receptor is the nicotinic Ach receptor (nAchR) at the neuromuscular junction. Ach released from the terminals of a motoneuron binds nAchRs located in high density on the post-synaptic membrane at the endplate. The nAch receptor is composed of 5 subunits ( " 2 #!$ ). Each subunit contains 4 transmembrane segments and each subunit is arranged like the stave of a barrel around a central pore which forms a cation selective ion
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1. Transmitters - 1 of 8 Transmitter systems of the central...

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