Signal transmission synaptic

This membrane fusion process (outside the brain) is known to involve thousands of single membrane units, previously thought of as vesicles, assembled into units that have been termed "boutons". We have examined the EM texture of the boutons and found that they are in fact a cubic phase. The synaptic signal transmission can take place as frequently as hundreds of times per second. A fusion process involving a hyperbolic membrane can be well controlled, and the calcium ion influx - which induces fusion - is expected to change the conformation of the cubosome surface membrane from its planar bilayer conformation to the fusogenic saddle-saddle conformation. (It is known phase transitions of membrane lipids can occur when exposed to calcium, e.g. [40]). 

Neurons rely upon a ready supply of cholesterol for maintaining a broad array of physiological functions such as membrane synthesis, myeUn maintenance, electrical signal transduction, synaptic transmission, and plasticity. Cholesterol metabolism in the CNS is unique compared with the rest of the body. Because of the existence of the blood-brain barrier (BBB), almost all the sterol required for new membranes comes from de novo synthesis within the CNS [33]. In addition, the brain has evolved highly efficient mechanisms to maximize the utihzation of cholesterol. UnUke other membrane lipid components, cholesterol cannot be synthesized at neuronal terminals. Therefore, synaptic function depends largely on cholesterol supplied from either axonal transport from the cell body and or uptake of Upidated ApoE produced by astroglia via neuronal lipoprotein receptors. 

The mechanism of action for many naturally occurring chemicals requires a short half-life (e.g., see Figure 5.21), which is often provided by the presence of degrading enzymes. Neurotransmitters, which are released by the presynap-tic neuron for signal transmission across the synapse, must be rapidly removed from the synaptic space removal is essential to restoring susceptibility to sub-... 

I.3. Synaptic Potential. A postsynaptic membrane may be considered as a chemosensory membrane. The signal transmissions through most synaptic regions (the region where one nerve ending terminates at a dendrite of another nerve cell) are mediated by chemical transmitters released from the nerve end upon the arrival of an action potential (Table 25). In some synapses, the two membranes are so closely adhered that the electrical impulse (action current) will directly initiate a synaptic potential at the second cell (i.e., an electrical synapse (Fig. 43A)). However, in a chemical synpase, the chemical transmitters released from the presynaptic terminal diffuse and react at a certain part of the dendrite membrane (postsynaptic membrane) where chemical receptors are located. The chemical transmitters react with the... 

The actual transmission of signals across a synaptic junction is a complicated chemical process that depends on a release of a neurotransmitter from the trans-... 

Of the several classes of receptors for endogenous chemical signals [3], two are used as postsynaptic receptors in synaptic transmission ligand-gated ion channels (LGICs) and G protein-coupled receptors (GPCRs Fig. 1). Due to the large number of transmitters and the existence of several receptor types for almost all, postsynaptic receptor activation is the most diversified step of synaptic transmission. Table 1 shows selected neurotransmitter receptors. 

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