Myelin increases resistance across the cell membraneby granpa Tags: action potential, axon, ion channels, myelin, neuron 

#19
Sep2408, 04:12 AM

PF Gold
P: 716

If the capacitance is effectively 50 time less with the wrapping of myelin, you forgot a crucial parameter in your computation: length => area. if a node is 2.2 pF for 0.5 µm then an internode (1 mm) is (2.2/50)*2000= 88 pF. Did I said Divergence? 



#20
Sep2408, 06:25 AM

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#21
Sep2408, 06:52 AM

PF Gold
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#22
Sep2408, 08:40 AM

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#23
Sep2408, 09:26 AM

PF Gold
P: 716

I have some difficulty with your reply:
A cylindrical resistance is proportional to volume => proportional to length. http://en.wikipedia.org/wiki/Electrical_resistance A plane capacitor is proportional to area => proportional to length. http://en.wikipedia.org/wiki/Capacitor#Capacitance See computations => http://butler.cc.tut.fi/~malmivuo/bem/bembook/21/21.htm I'm consistent. Where did you find a unit of ohm*cm²? 



#24
Sep2408, 04:16 PM

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P: 16,488

Note Gm listed in your last reference (http://butler.cc.tut.fi/~malmivuo/bem/bembook/21/21.htm). Conductance/unit area is simply the inverse of area specific resistance and is, IMO, more convenient. 



#25
Sep2408, 08:41 PM

Sci Advisor
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#26
Sep2408, 11:44 PM

PF Gold
P: 716

I bought the book of Koch. I'll see. I'll ask Ted Carnevale... Edit: I'm unable to draw the equivalent circuit since the capacitor must be oriented to the external milieu but connected to the internal one. The resistance must be longitudinal. It gives a worst solution than before. 



#27
Sep2408, 11:52 PM

PF Gold
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#28
Sep2508, 12:29 AM

PF Gold
P: 716

http://www.pubmedcentral.nih.gov/pic...8&blobtype=pdf http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum The time constant is already 10 fold too high. 



#29
Sep2508, 06:33 AM

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Capacitance is proportional to area/distance. So capacitance is inversely proportional to length if you wish to say it that way. (Although "distance" is a better description of the separation between plates than "length" since "length" connotes the largest dimension of an object and the separation between the plates is the smallest dimension) 



#30
Sep2508, 06:50 AM

PF Gold
P: 716

we are speaking about the area of the plates, here.
the distance between the plates, d was already implied. two plates of an area of A and separated by a distance d. C is proportional to A and inversely proportional to d since C =e*A/d Thus if A is augmented (internode), even if d is augmented, C is augmented since a node has a length of L1= 0.5 µ => area = 2*pi*R*L1 => 2.2 pf the same plates where d is *50 => C/50 an internode is 2000 time longer 2*pi*R*L1*2000 => (2.2/50)*2000 = 88 pf and the computation is simplified since the perimeter augments with each wrap => C>88pf 



#31
Sep2508, 07:05 AM

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#32
Sep2508, 07:10 AM

PF Gold
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DaleSpam,
Give the results in our example. 50 turns of myelin (50*d) and a length that is 2000 time longer (2000*A). 



#33
Sep2508, 07:55 AM

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#34
Sep2508, 08:54 AM

PF Gold
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Please give us your result (and computation)? 



#35
Sep2508, 10:16 AM

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It is very difficult for me to communicate with you. I know that a large part of that is a language barrier, so I am trying to be patient. 



#36
Sep2508, 01:39 PM

P: 2,258




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