Synaptic transmission and neurochemistry 1

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neurocrine
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an electrical signal that travels along a nerve cell until it reaches the very end of the cell, where it is translated into a chemical signal secreted by the neuron
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neurotransmitter
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diffuse across a small gap to the target cell rapid
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neuromodulator
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acts more slowly as an autocrine/paracrine signal
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neurohormone
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chemicals released by neurons into the blood for distribution
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electrical synapses
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electrical current flowing from one neuron to the other
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chemical synapses
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chemical transmitters transfer info from one neuron to the other
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loewi vagustoff
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electrical stimulation of axons innervating frog heart released chemical that mimicked effects of neuron stimulation on hearbeat vagustoff released, acetylcholine
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gap junctions
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where direct transfer of ionic current from one cell to the next occurs formed with 2 connexons- one from each cell aplyasia tail and ink firing
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mammalian brain and gap junctions
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formed between glial cells astrocytes are interconnected through gap junctions – glial network
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gap junctions between neurons
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generation of AP in one neuron causes small amount of current to flow through gap junctions into a second neuron
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chemical synapses presynaptic element
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usually axon mitochondria secretory granules synaptic vesicles active zones
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chemical synapses postsynaptic element
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usually dendrite postsynaptic density: receptors and enzymes accumulate just under membrane
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types of synapsese in CNS
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axodendritic axosomatic axoaxonic dendrodendritic
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neurotransmission process
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neurotransmitter synthesis load into synaptic vesicle vesicles fuse to presynaptic membrane neurotransmitter released binds to postsynaptic receptors neurotransmitter removal from the synaptic cleft
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5 types of neurotransmitter chemicals
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amines acetylcholine peptides amino acids purines, gases, lipids
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amines made with three amino acids…
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tyrosine, trytophan, histidine dopamine, serotonin, histamine
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glutamate gaba ^amino acids
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excitatory, depolarization inhibitory (entry of Na, Ca), hyperpolarization (entry of Cl-)
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neurotransmitter release
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arrival of AP in axon terminal depolarization voltage gated Ca channels open Ca enters exocytosis of vesicles and release of content in synaptic cleft vesicle membrane recovered by endocytosis
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release of peptide transmitters
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by secretory granules, Ca dependent requires high frequency firing release of peptides takes longer
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termination of neurotransmitter activity
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diffusion reuptake enzymatic degradation
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receptors of neurotransmitters
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over 100 2 major classes ionotropic metabotropic
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ionotropic receptor
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receptor channel ligand-gated ion flow
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metabotropic receptor
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G-protein coupled receptors (GPCRs) ion channel/enzyme activity
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basic signal transduction
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signal molecule (ligand) membrane receptor intracellular signal molecules target proteins response SIGNAL AMPLIFICATION
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second messengers
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cAMP, cGMP, IP3, DAG, Ca2+
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how second messengers are formed AC GC PLC
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Atp>cAMP GTP>cGMP membrane phospholipids> IP3 + DAG
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GPCRs
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when activated: open an ion channel in the membrane alter enzyme activity in cytoplasm through AC and PLC
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cAMP pathway
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AC catalyzes cAMP from ATP decrease in cAMP, decrease of PKA
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PLC pathway
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cleaves phospholipid into two messengers IP3 and DAG ligate receptors, binds and opens up then Ca released from smooth ER DAG finds PKC and activates phophorylation
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electrical vs chemical synapses
electrical vs chemical synapses
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ELEC=IONS CHEM=NEUROTRANS

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