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4. NTs bind to receptors in the postsynaptic membrane
5. This opens specific ion channels in the postsynaptic membraneEither Excitatory (allowing cations in)Or inhibitory (allowing anions in)6. NT molecules are either inactivated by enzymes or removed by transporters oPresynaptic activitySynaptic vesicles are about 50 nanometers in diameterThey fuse with the presynaptic membrane with is called exocytosisExocytosis is mediated by proteins called SNAREs V-SNARES are attached to vesiclesT-SNARES are attached to the membraneV-Snares and t-Snares attach to each other, docking the vesicle to the membraneA third protein synaptotagmin senses calcium, finalizing the fusion between vesicles and membrane – Ejects NTs into synaptic cleftoPostsynaptic Postsynaptic membranes are studded by receptor moleculesLock and key principleA specific NT can only fit into a specific receptor proteinThis is because it has the correct ligandThe postsynaptic activity is determined by the type of receptorThere are gated ion channels that are important in NT-receptor interactionsLigand-gates ion channels, also called ionotropic receptors, open an ion channel when an NT binds to themA separate type of receptor does not directly control an ion channelInstead the active molecules know as G-proteinsThese G proteins -----oLigandsA ligand is a substance that binds to a receptorAn 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 functionNoncompetitive (agonist/antagonist) ligands that bind to a different part of the receptor (neuromodulator)Two types of receptorsLigand gated /ionotropicG protein-coupled / metabotropic oShutting down the signalDegradationNT is broken down an enzymeReuptakeRepacked into vesicles and sent back to presynaptic neuron
------Electrical synapseoA non-chemical, ultra-fast way to convey informationSynaptic clefts are usually around 20-40 nanometersSome are only a tenth of thatIn those, called gap junctions or electrical synapses, no NT/receptors pairings areneededInstead, large channels can reach directly from one cell into the next allowing fordirect ion flowTransmission here is similar to direct transmission of an AP down an action potentialThese ultra-quick connections are mostly found In circuits that mediate escape behaviorsIn circuits that need synchronous activation, such as for eye movementsNeurotransmittersoDefinitionA substance that exists in presynaptic axon terminalsThe pre cell contains enzymes to synthesize the substanceAction potentials lead to a release of the substanceThe postsynaptic membrane has receptors for the substanceThe substance produces changes in postsynaptic cellsBlocking the substance prevents the effects---o