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SUMMARY:Biophysics of wiring the brain - Aldo Faisal\, Department of Zoolo
 gy\, University of Cambridge
DTSTART:20070213T130000Z
DTEND:20070213T140000Z
UID:TALK5826@talks.cam.ac.uk
CONTACT:Cordula Becker
DESCRIPTION:Action Potentials are typically used by axons to\ntransmit inf
 ormation rapidly and reliably. Yet\, the reliability\nof transmission alon
 g fibers below 0.5 micrometer diameter\, \nsuch as cortical collateral and
  cerebellar axons\, is unkown.\n\nI will show how conduction along such th
 in axons \nis affected by the probabilistic nature of voltage-gated \nion 
 channels mediating the spike. I address this problem \nusing biophysically
  realistic stochastic simulations \nand modelling up to a million individu
 al ion channels.\n\nThe three key findings are that fluctuations in single
  Na channels \nset a general lower limit to unmyelinated axon diameter \na
 t 0.1 micrometer. This limit operates above other biophysical\nlimits to a
 xon diameter and matches the smallest known axons \nacross the animal king
 dom. \nIn axons below 0.5 micrometer\, such as the average pyramidal cell\
 ncollateral and parallel fibers in cerebellum\, channel noise introduces \
 nhistory-dependent spike time jitter in the order of milliseconds.Reliabil
 ity \ndecreases the further action potentials have to travel and channel n
 oise \nproduces a novel mode of action potential propagation: stochastic \
 nmicro-saltatory conduction.\nFinally axonal channel noise causes variabil
 ity of the action potential wave \nform - which could partially explain fl
 uctuations in transmitter release at central \nsynapses\, innervated typic
 ally by thin axons. \n\nIn conclusion\, these findings will be related to 
 noise constraints on \nneural coding to cell design and allow prediction o
 f cortical circuit anatomy. \n
LOCATION:Seminar Room (ground floor)\, Craik-Marshall Building
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