Neurotransmitters synaptic transmission model

Some neurons can fire several hundred times per second, secreting neurotransmitter each time. Synapses are remarkable secretion machines destined to undergo millions of repeated exocytic cycles in their lifetime. So how does this process work so fast and so efficiently Answers have gradually emerged from the work of many different laboratories and model systems [73, 74]. An exhaustive description is beyond the scope of this chapter, but a summary of key events and specializations of the synaptic vesicle cycle is useful. This will show how synaptic transmission is optimized spatially and biochemically (see also Chs 6,10 and 22). 

One of the major problems in thinking about dopamine neurotransmission is the number of features which do not fit into the textbook model of classical synaptic transmission, based on the neuromuscular junction. These include an extremely wide divergence of release sites of a single axon, extrasynaptic location of receptors, termination of neurotransmitter action by diffusion and uptake from extrasynaptic sites, and significant overflow of neurotransmitter from the synaptic cleft into the extracellular space. 

FIGURE 5.5 A simple model of synaptic transmission. The pres)fnaptic neuronal membrane (green) releases the netirotransmitter (triangles) in the synaptic deft. The neurotransmitter travels through the synapse and eventually binds to a receptor (blue) expressed by the postsynaptic neuronal membrane. If the neurotransmifter is soluble in water, it will bind to a surface-accessible region of its receptor. The postsynaptic membrane is represented with a lipid bUayer (cholesterol in red, phospholipids in green). 

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