4 NTs bind to receptors in the postsynaptic membrane 5 This opens specific ion

4 nts bind to receptors in the postsynaptic membrane

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4. NTs bind to receptors in the postsynaptic membrane
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5. This opens specific ion channels in the postsynaptic membrane Either Excitatory (allowing cations in) Or inhibitory (allowing anions in) 6. NT molecules are either inactivated by enzymes or removed by transporters o Presynaptic activity Synaptic vesicles are about 50 nanometers in diameter They fuse with the presynaptic membrane with is called exocytosis Exocytosis is mediated by proteins called SNAREs V-SNARES are attached to vesicles T-SNARES are attached to the membrane V-Snares and t-Snares attach to each other, docking the vesicle to the membrane A third protein synaptotagmin senses calcium, finalizing the fusion between vesicles and membrane – Ejects NTs into synaptic cleft o Postsynaptic Postsynaptic membranes are studded by receptor molecules Lock and key principle A specific NT can only fit into a specific receptor protein This is because it has the correct ligand The postsynaptic activity is determined by the type of receptor There are gated ion channels that are important in NT-receptor interactions Ligand-gates ion channels, also called ionotropic receptors, open an ion channel when an NT binds to them A separate type of receptor does not directly control an ion channel Instead the active molecules know as G-proteins These G proteins ----- o Ligands A ligand is a substance that binds to a receptor An agonist is a ligand (ex: a drug) that initiates the normal effects of the receptor (opening a channel or sending a second signal) An antagonist is a ligand that binds to a receptor but does not activate it (blocking it) An inverse agonist binds to the receptor and reverses the normal function Noncompetitive (agonist/antagonist) ligands that bind to a different part of the receptor (neuromodulator) Two types of receptors Ligand gated /ionotropic G protein-coupled / metabotropic o Shutting down the signal Degradation NT is broken down an enzyme Reuptake Repacked into vesicles and sent back to presynaptic neuron
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------ Electrical synapse o A non-chemical, ultra-fast way to convey information Synaptic clefts are usually around 20-40 nanometers Some are only a tenth of that In those, called gap junctions or electrical synapses, no NT/receptors pairings are needed Instead, large channels can reach directly from one cell into the next allowing for direct ion flow Transmission here is similar to direct transmission of an AP down an action potential These ultra-quick connections are mostly found In circuits that mediate escape behaviors In circuits that need synchronous activation, such as for eye movements Neurotransmitters o Definition A substance that exists in presynaptic axon terminals The pre cell contains enzymes to synthesize the substance Action potentials lead to a release of the substance The postsynaptic membrane has receptors for the substance The substance produces changes in postsynaptic cells Blocking the substance prevents the effects--- o
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