The above drawing highlights the key parts of a generic neuron. Although the sizes and shapes of neurons can vary dramatically between simple animals like C. elegans and complex animals like humans, they all function fundamentally the same and share the same basic parts. A neuron has to develop and maintain these parts through the regulated active transport of cargoes, which literally means using molecular nano-motors to haul cargos long distances. All neurons have a cell soma, containing various organelles, one or more dendrites (which receive information), and a single axon, which can be very long and intricately branched (but is usually not branched in C. elegans). Part of the axon is specialized to form synapses, which integrate and transmit information to other neurons or muscle cells.
Each presynaptic region contains a “dense projection”, which is a small structure around which synaptic vesicles are clustered. Synaptic vesicles fuse with the plasma membrane and release small molecule neurotransmitters from the active zone around this structure. The synaptic vesicles then endocytose and recycle locally (at the synapse) and refill with neurotransmitter. The synaptic region also contains larger Dense Core Vesicles that release neuropeptides. Dense Core Vesicles do not recycle, so they must be continually delivered from the cell soma.
Each presynaptic region contains a “dense projection”, which is a small structure around which synaptic vesicles are clustered. Synaptic vesicles fuse with the plasma membrane and release small molecule neurotransmitters from the active zone around this structure. The synaptic vesicles then endocytose and recycle locally (at the synapse) and refill with neurotransmitter. The synaptic region also contains larger Dense Core Vesicles that release neuropeptides. Dense Core Vesicles do not recycle, so they must be continually delivered from the cell soma.
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This is a blown-up drawing of a single synapse. Our brains are packed with trillions of these biological transistors. The cell biology and biochemistry in these little structures produce all of our movements, our perceptions, even our thoughts, memories, and feelings.
Below is an image of rat brain sections in which all the synapses fluoresce green. As you can see, it is often difficult to see order in how the synapses are arranged. Sometimes they are packed together so tightly that individual synapses can't be distinguished (see "Granule Layer Synapses" below). And yet, by a baffling process, things like beautiful innate animal behaviors, and, yes, even human thought, emerge from jumbles of connections like this. The key to neuronal communication is synaptic transmission, which occurs when Synaptic Vesicles or Dense Core Vesicles fuse with the membrane and release neurotransmitters or neuropeptides that stimulate receptors on the post-synaptic cell.
We are interested in the underlying signaling pathways and cell biology that regulate the production and movements of synaptic vesicles and dense core vesicles. Some of the signals we study seem to determine how much synaptic transmission occurs at synapses, in some cases possibly even turning synapses ON or OFF to establish and maintain behaviors and bring order to this apparent chaos.