Lecture 21 – Nervous System III

Specialized region that is loaded with vesicles

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Specialized region that is loaded with vesicles Docked along membrane but not yet releasing NT Postsynaptic cell – 10-20 nm away Postsynaptic density High density of receptors Synaptic cleft Proteins, NT, chemicals, enzymes V-gated calcium channels Will open on the presynaptic cell when an AP reaches the end Induces synaptic vesicles to fuse with PS membrane and dump NT into cleft Diffuse and bind .Dendritic spines axon terminal can end on any part of a dendrite can end on cell body or hillock Types of synapses Can synapse anywhere on the neuron The closer you are to the axon hillock, the greater the likelihood the neuron will reach  threshold Signal Transmission Axon terminal depolarizes – due to arrival of AP Voltage gated Ca channels open and Ca enter the axon terminal down its concentration  gradient Increase in intracellular Ca triggers vesicle docking and fusion of vesicles with the  presynaptic membrane, releasing neurotransmitter into synaptic cleft Neurotransmitter molecules diffuse across the synaptic cleft and some bind to receptors  in the postsynaptic membrane Binding of NT molecules to receptors in the region of the postsynaptic density Synaptic signaling via g-protein signaling
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Can open ion channels or activation of a g-protein channel Net effect is generally positive because Na is flowing in  This is bigger than the flux of K because Na electrochemical gradients are non  competitive Result in a graded potential Inhibitory lets potassium out or does something that hyperpolarizes NT diffuses away from the receptors and are removed by diffusion, degradation,  enzymatic degradation, and reuptake into the presynaptic cell NT Release Opening of calcium channels Before any AP gets there, there are already vesicles containing NT dicked in the active  zone Interaction between proteins on the vesicle and the set of proteins on the membrane Held in a loosely connected condition SNARE proteins Synaptotagmins  Ca binds to them and changes configuration of docking SNARE proteins and will wind  membranes down so that they can fuse After Fusion Vesicles can completely fuse with the membrane and are later recycled by endocytosis  in areas outside the active zone Vesicles at synapses where the frequency of AP is high, the vesicles fuse only briefly  while they dump NT and then reseal the synaptic membrane and detach, pulling back  into the synaptic terminal
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