❏ Open voltage-gated calcium channels, Ca enters the terminal ❏ Cat 2 causes synaptic vesicles to bind to presynaptic membrane ❏ Vesicles burst open and release contents ❏ Nt DIFFUSES ACROSS CLEFT AND BINDS TO RECeptors ❏ Nt becomes unbound- reuptake into vesicles, removal from cleft ❖ Two Types of Receptors ➢ Ionotropic Receptors ■ NT diffuses across cleft and binds to receptors. If the receptor is an ionotropic receptor, it is connected to an ion channel, which opens and allows ions to enter or leave the neuron. This reduces a fast response: EPSP or IPSP ■ Primary response *Metabotropic Receptors NT diffuses across cleft and binds to metabotropic receptors (e.g a dopamine receptor) - If the receptor is a metabotropic receptor, it is connected to a G protein, which can activate either an ion channel or additional chemical messenger w/n neurons. Process is slower - Secondary response 1. Diffusion ➔ NT becomes unbound from the receptor, and then must deactivated ➔ The Nt CAN BE REMOVED FROM BY SIMPLE DIFFUSION & is often there us uptake by glial processes close to the synapse (might eat up the NT) (glutamate syapse)- Deactivating enzymes ◆ An enzyme can be used to deactivate the NT, for example acetylcholinesterase (AcHe) inactivated acetylcholine (ACh) Reuptake - NT becomes unbound from the receptor - The nt along w. Parts of the synaptic vesicles is reabsorbed (reuptake) at the nerve terminal by transporter proteins & then this material is used to make new synaptic vesicles - Now common psychotropic drugs like SSRis are reuptake inhibitors that are selective for on NT such as serotonin - But if neurons may never produce enough serotonin, so it is ok to stay on these drugs for a long time Definitions a. Competitive- blocks binding siteNon-competitive- doesn’t prevent binding but NT has no effect ● Ligand = a chemical that binds to a receptor and may or may not be a NT● Affinity= how well a compound binds to a receptor, A ligand may bind to one receptor type very well -Can modulate synapses ● No drug has just one action in the nervous system ● A drug may have a primary effect BUT there are always side effects- different pathways use the same NT the drug binds to other receptor at lower affinities ● The events at chemical synapses are the major target for medication and drugs of abuse Glutatement also involved in excitotoxicity, High levels of extracellular glutamate can result in cell death by elevating the intracellular calcium -Two Major Dopamine Systems- - Reward: mesolimbocortical pathway: ventral tegmental area to the nucleus accumbens, cortex, and hippocampus - Mesostriatal pathway: substantia nigra to striatum