Leech Mechanosensory Neurons: Synaptic Facilitation by Reflected APs (Baccus 1998)

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This model by Stephen Baccus explores the phenomena of action potential (AP) propagation at branch boints in axons. APs are sometimes transmitted down the efferent processes and sometimes are reflected back to the axon of AP origin or neither. See the paper for details. The model zip file contains a readme.txt which list introductory steps to follow to run the simulation. Stephen Baccus's email address: baccus@fas.harvard.edu
1 . Baccus SA (1998) Synaptic facilitation by reflected action potentials: enhancement of transmission when nerve impulses reverse direction at axon branch points. Proc Natl Acad Sci U S A 95:8345-50 [PubMed]
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Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism:
Cell Type(s): Leech pressure (P) mechanosensory neuron;
Channel(s): I K; I K,Ca; I Sodium; I Calcium; I Potassium;
Gap Junctions:
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Pattern Recognition; Activity Patterns; Spatio-temporal Activity Patterns; Influence of Dendritic Geometry; Detailed Neuronal Models; Synaptic Plasticity; Short-term Synaptic Plasticity; Axonal Action Potentials; Action Potentials; Facilitation; Invertebrate;
Implementer(s): Baccus, Stephen [Baccus at fas.Harvard.edu];
Search NeuronDB for information about:  I K; I K,Ca; I Sodium; I Calcium; I Potassium;
TITLE Sodium ion accumulation   
: Sodium ion accumulation inside and outside   
   SUFFIX na   
   USEION na READ ina, nai, nao WRITE nai, nao   
INDEPENDENT {t FROM 0 TO 1 WITH 10 (ms)}   
UNITS {   
   (molar) = (1/liter)   
   (mV) = (millivolt)   
   (um) = (micron)   
   (mM) = (millimolar)   
   (mA) = (milliamp)   
   FARADAY = 96520 (coul)   
   R = 8.3134     (joule/degC)   
   celsius=20     (degC)   
   nabath = 115   (mM)   
   diam = 1 (um)   
   ina            (mA/cm2)   
STATE {   
   nai START 10 (mM)   
   nao START 115  (mM)   
   nai = _ion_nai;   
   nao = _ion_nao;   
   SOLVE state METHOD derivimplicit
DERIVATIVE state {   
   nai' = -ina * 4/(diam*FARADAY) * (1e4)
   nao'= 0
This model uses ina but does not WRITE it; thus this model does   
not add anything to the total ionic current.   
The initial block works around a difficulty that arises from a STATE in   
this model having the same name as an ion.  (Note: in the cabpump model   
there is no name conflict between the ca[] states and the cai ion   
concentration.) The sequence of events when finitialize is called is   
that the na_ion's nai,nao are initialized to the global variables   
nai0_na_ion and nao0_na_ion respectively. Then this model's INITIAL block   
is called. By default, nai/nao would be set to the initial state values   
nai0/nao0 implicitly declared in this model and on exit from the intitial   
block, the na_ion values would be assigned these local values. We therefore  

directly set the local state values to the na_ion values. See the   
"nocmodl nacum" generated nacum.c file to see the precise sequence on   
the nrn_init() call.   
diam is a special range variable in NEURON and refers to the diameter in   
microns.  Under scop and hocmodl its default value is specified in the   
PARAMETER block. In NEURON, however, its value is taken from the   
"morphology" mechanism.