Synapse definition

By definition, learning is the acquisition of new information, whereas memory is the retention of acquired information. Driven by knowledge obtained by scientists before them, various disciples of neuroscience over the course of the past 100 years have learned more about various components of learning and memory, whether at the molecular level of synapses or at the systems level of brain circuitry. The concept of memory of mind has existed since the time of Aristotle. It is only during the past 50 years or so that scientists have begun to unravel some of the anatomical and cellular bases underlying such a complex mental process. 

Like Prozac and Paxil, MDMA also increases serotonin levels in the brain. The similarities end there, however. Doctor-prescribed anti-depressants are both safe and effective. Ecstasy is definitely not safe, and after the first use, becomes less safe and less effective. The primary effect of MDMA in the brain is to increase greatly the amount of serotonin in the brain s synapses (the areas in between two brain cells where signaling takes place). MDMA does this by interfering with the neurons ability to remove serotonin from the synapse after it is released (Figure 2.2). When serotonin is released normally, under drug free conditions, it stimulates the receiving neuron and is quickly taken back up into the neuron that released it in the... 

Rosenmund C, Stevens CF (1996) Definition of the readily releasable pool of vesicles at hippocampal synapses. Neuron 16 1197-1207... 

The definition of a synapse requires at least the presence of a presynaptic element containing a concentration of vesicles and an apposed postsynaptic element, from which it is separated by the synaptic cleft (Peters et al., 1991). The vesicles of the dopamine synapses are concentrated around the points of synaptic contact rather than around the mitochondria that are part of the varicosities, so the release is probably punctate from the synaptic active zones. Notwithstanding the existence of synaptic specializations and... 

A brief comparison between electrical and chemical synapses, however, is instructive. Electrical transmission, by definition, requires no chemical substance for the transmission of an electrical signal from one neuron to another rather, electrotonic impulses are thought to move from one cell to another via syncytoid connections. The rate of transmission is orders of magnitude faster in electrical, as versus chemical, synapses. Although inhibition of chemical transmission can occur in a variety of ways (i.e., inhibition of... 

When an action potential traveling down the axon of a motoneuron reaches the myoneural endplate, a process occurs that releases acetylcholine into the synaptic cleft and consequently depolarizes the postsynaptic membrane. A similar process probably occurs at cholinergic synapses in the central nervous system. In 1950 Fatt and Katz discovered a spontaneous subthreshold activity (MEPP) of motor nerve endings and were thereby led to the concept that acetylcholine is released in definite units (quanta) of 10 to 10 molecules. Electron microscopy subsequently revealed characteristic vesicles about 40 nm in diameter, clustered near presynaptic membranes. Subcellular fractionation procedures were devised by Whittaker and de Robertis for the isolation of these vesicles from brain homogenates in sucrose density gradients, and it was soon demonstrated that they were indeed concentrated reservoirs of acetylcholine. The hypothesis that the vesicles discharge the quanta of transmitter became irresistible. 

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