Post on 01-Jun-2018
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Initiation or Generation of a Nerve
Impulse (Action Potential)
At rest, the voltage-sensitive sodiumand potassium gates in the channels in
the plasma membrane of a nerve cell
are nearly closed and the Na+
!+
pumpmoves " Na+ions to the #$% and & !+
ions to the I$%'
his contributes to the formation of aresting membrane potential of -*
millivolts (m)'
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esting embrane oltage
()
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Initiation of the Nerve Impulse $ontinued.
he sodiumpotassium pump alsocontributes to the resting membrane
potential by pumping out three sodium
ions to the #$% and pumping in t/o
potassium ions to the I$%'
he effect of this process is to ma0e
the outside of the nerve cell positive
compared to the inside of the cell /hich
becomes negative (-* m)'
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Initiation of the Nerve $ell Impulse
$ontinued.
At rest, the I$% of an a1on has a
voltage of about -* m
2hen the membrane of the a1on isproperly stimulated, Na+ions begin to
lea0 into the I$%' his causes the
voltage to change to a less negative
state'
2hen I$% voltage reaches a threshold
of about - 33 m, sodium gates open'
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Initiation of the Nerve Impulse $ontinued.
As sodium gates open, Na+
flo/through sodium channels increases and
4uic0ly changes the voltage from a
resting level of - * m to + "*m' his rapid shift from a negative to a
positive state is called
5#P67AI8AI6N'
At +"* m, the sodium gates close'
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Initiation of the Nerve Impulse $ontinued.
2hen the sodium gates close at +"*m, the depolari9ation process stops'
Interestingly, the + "* m condition
causes the potassium gates to open andallo/s potassium to flo/ from the I$% to
the #$%'
he potassium flo/ 4uic0ly reverses thepotential from + "* m to about -
*m' his is called
#P67AI8AI6N'
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Initiation of the Nerve Impulse $ontinued.
he rapid depolari9ation andrepolari9ation process generates a avoltage pulse pea0 that is called the
A$I6N P6#NIA7 or N##IP:7;#'
he formation of a nerve impulsestimulates the formation of still anothernerve impulse in the ne1t section of thea1on membrane
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Nerve Impulse 5iagram
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6vervie/ of ransmission of Nerve Impulse
Action potentialsynaptic 0nobopening of $a+ channelsneurotransmitter vesicles fuse /ith membrane
release of neurotransmitter into synaptic cleftbinding of neurotransmitter to protein receptor
molecules on receiving neuron membraneopening of ion channelstriggering of ne/ action potential
Neurotransmitter is bro0en do/n by en9ymes< ion channels close -- effect brief and
precise
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=o/ a synapse /or0sNervefiber(axon)
Action
potential
Ca + +
Transmitter
Receptor
Voltage-sensitivechannel