ULTIMATE COMPUTING - Quantum Consciousness Studies

62 From Brain to Cytoskeleton
resistance pathway (which may be networks of extracellular protein filaments
known as “synapsin”). The sites for electrical communication between cells have
been identified in electron micrographs as gap junctions in which the usual
intercellular space of several tens of nanometers is reduced to about two
nanometers. There appear to be a huge number of electrical synapses in
mammalian brain (estimated to be as high as 80 percent of all synapses), but
because of difficulties in isolation, characterization, and inability to study them by
pharmacological manipulation, their significance remains unknown. Chemical
synapses have been extensively studied.
At chemical synapses the fluid gap between presynaptic and postsynaptic
membranes prevents a direct spread of current and the lack of an electrical
connection between neurons. The synaptic bouton contains large quantities of
spherical vesicles (about 50 nanometers diameter) which contain neurotransmitter
molecules. Acetylcholine, norepinephrine, serotonin, dopamine, gamma amino
butyric acid (GABA) and various peptides and amines have been identified as
neurotransmitters. Some are excitatory while others (i.e. GABA) are inhibitory.
Figure 4.1: Neuronal organization: 1) Branching dendrites (top) entering cell body
or perikaryon; branching axons exiting at bottom. 2) Axons forming synapses on
dendrites and cell body. 3) Axon surrounded by 100 layers of myelin which
increases conduction velocity; structures visible in axon include mitochondria,
neurotransmitter vesicles, and microtubules. 4) Synaptic cleft; neurotransmitter
vesicles (top right) fuse with membrane as they are released. By Paul Jablonka.