Nanomedicine, Volume I: Basic Capabilities
© 1999 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999
220.127.116.11 Direct Synaptic Monitoring
The synaptic cleft between the axonal presynaptic terminal and the dendritic postsynaptic membrane is 10-20 nm in most synapses, although in the vertebrate myoneural junction it may be as large as 100 nm. Contact area per bouton is ~1 micron2, giving a total gap volume of ~107-108 nm3. The density of acetylcholine receptors is highest in muscles along the crests and upper thirds of the junctional folds (~10,000/micron2), and is lowest in the extrasynaptic regions (~5/micron2).802 (Other neurotransmitters exist; Table 7.2 and Section 18.104.22.168.) Each action potential discharge triggers the release of ~104-105 molecules of acetylcholine into the gap volume of an active neuromuscular junction (diffusion time ~1 microsec), raising cligand from near zero to ~3 x 10-4 molecules/nm3 (~0.0005 M)531 in ~1 millisec, followed by near-complete hydrolyzation by acetylcholinesterase during the 1-2 millisec refractory period. Into the gap volume may easily be inserted a ~105 nm3 neurotransmitter concentration sensor (Section 4.2.3) able to measure ~100 acetylcholine molecules in ~1 millisec (Eqn. 4.5), thus detecting pulses at the fastest discharge rate. A similar device could be used to precisely regulate neuro-transmitter concentration at the junction, and hence the neural signal itself, under nanodevice control (Section 22.214.171.124). Simple electrochemical and mechanochemical artificial synapses have been demonstrated.499
Last updated on 17 February 2003