nirvanamona
Forum Senior
Topics: 6
Posts: 28
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yes i figured my mistake by now....what i know bout velocity of nerve conduction is that large myelinated fibres have the fastest nerve conduction.
incidentally i looked up guyton and i found this:-
Saltatory conduction is of value for two reasons. First, by
causing the depolarization process to jump long intervals along
the axis of the nerve fiber, this mechanism increases the veloc-
ity of nerve transmission in myelinated fibers as much as 5-
fold to 50-fold. Second, saltatory conduction conserves energy
for the axon because only the nodes depolarize, allowing per-
haps 100 times less the loss of ions than would otherwise be
necessary and therefore requiring little metabolism for reesta-
blishing the sodium and potassium concentration differences
across the membrane after a series of nerve impulses.
Still another feature of saltatory conduction in large myeli-
nated fibers is the following: The excellent insulation afforded
by the myelin membrane and the 50-fold decrease in mem-
brane capacitance allow repolarization to occur with little
transfer of ions. Therefore, at the end of the action potential,
when the sodium channels begin to close, repolarization oc-
curs so rapidly that many of the potassium channels have not
yet begun to open. Therefore, conduction of the nerve impulse
in the myelinated nerve fiber is accomplished almost entirely
by ion conduction through the voltage-gated sodium channels,
with very little contribution by the potassium channels.
could the answer be D?
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| pocas
Forum Elite
Topics: 7
Posts: 169
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E
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| giovanni83
Forum Senior
Topics: 24
Posts: 125
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it's D
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| khorshid
Forum Guru
Topics: 32
Posts: 591
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can you explain plz?
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| muzammil
Forum Guru
Topics: 16
Posts: 658
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i know one thing its not a b and e but guys what is space constant of nerver fibre?
my intail guess baout eh answer was d but do not have a explanation.
can some one explain this.
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| giovanni83
Forum Senior
Topics: 24
Posts: 125
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The answer is d. (Berne, 3/e, pp 34–36.) In order for propagation of
an action potential to occur, the depolarization produced by one action
potential must depolarize the adjacent patch of excitable membrane to
threshold. The amount of charge that must flow to produce this depolarization
decreases as the capacitance decreases. Therefore, as the capacitance
decreases, conduction velocity increases. The flow of charge
decreases as the diameter of the nerve fiber decreases, therefore decreasing
the velocity of conduction. The space constant (Rm/Rin) is a measure of
how far along the axon the charge will flow. The smaller the space constant,
the greater the dissipation of charge through the membrane and therefore
the slower the propagation velocity. Decreasing (depolarizing) the resting
membrane potential inactivates sodium channels. This will decrease the
flow of charge across the membrane during an action potential and thus
decrease the velocity of propagation.
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| smalldoc
Forum Newbie
Topics: 0
Posts: 3
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amazing reply,i thought it was capacitance too,but couldnt explain myself
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| waqastariq
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capacitance very aptly answered...
capactiance is a measure of stored electiccal charge that must flow to depolarize a given AREA of neuron......so if MORE ions have to move...MORE slow dissipiation of charge and SLOWER depolarization ---> slower propagation...
and viceversa... hope this stupid explanation will help
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| vallia
Forum Guru
Topics: 98
Posts: 889
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 , it helped, thanks
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| lnb6des
Forum Newbie
Topics: 0
Posts: 5
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it's DD, u r right
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