Electrical Signals in Neurons
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Transcript of Electrical Signals in Neurons
Electrical Signals in Neurons
Ch. 12
ObjectivesDescribe the factors that maintain a resting
membrane potential.List the sequence of events that generates an
action potential.
Path of a Nerve Impulse
Path of a Nerve Impulse
Membrane PotentialsResting membrane potential – potential for
current to passCreated by a difference in charge between the
inside and outside of the cellMost cells are -70mVThe greater the difference, the greater the
potential Graded potential – a change in resting potentialAction potential – the passing of electrical
current as a result of the graded potentialThis is how neurons send signals
Resting Membrane Potential
Resting Membrane Potential – based on diffusionInside – more negative Outside – more
positiveHigh in K+
High in proteins (-)
- ions can’t leaveThis keeps inside more -
alsoK+ tends to diffuse out of
the cellThis results in an
increase – charge here
High in Na+
High in Cl-
K+ diffuses outThis results in an
increase + charge here
However, K+ will also go back inside because of attraction to - charge
Resting Membrane Potential – based on pump actionNa+ action
Will diffuse inwardThis could destroy RMP
sodium-potassium pumpPumps 3 Na+ out and 2 K+ inMaintains RMP
Action PotentialsAlso called impulseOccurs in 2 phases
Depolarizing phase Negative membrane potential becomes less
negative Reaches zero Then becomes positive
Repolarizing phase Membrane potential is restored to -70mV (RMP)
Action PotentialChannels
Na+ channels open Na+ rushes into the cell → depolarizing phase
K+ channels open K+ flows out → repolarizing phase
depol. and repol. last about 1msec (.001 sec.)
All-or-NoneWhen depolarization reaches the threshold (-
55mV) the action potential occursNo matter how great the difference is, it will
occurLike dominoes
It doesn’t matter how hard or soft your push the first domino, once you do all the rest will fall
Depolarizing PhaseInward movement of Na+ is favoredNa+ channels have 2 gates
Activation and inactivationIn resting state
Inactivation gate is open, activation gate is closed Na+ cannot move into the cell through these gates
At threshold (activated state)Both channels are open
Na+ rushes into the cell and depolarization occurs The more Na+ rushing in, the more channels open
Depolarizing PhaseAfter activation gates open, inactivation gates
closeInactivated channelNa+ – K+ pumps return to Na+ to the ECF
Repolarizing PhaseAt threshold – depolarization opens K
channelsThis allows K+ to flow out of the cell
the neuron is returned to resting state
Action Potential
ReviewDescribe a neuron at rest. Where are the
ions? What are the charges?List the steps in an action potential.
StepsRMP (-70mV)Action potential is triggered by
neurotransmitterDepolarization - Na+ gates open and Na+
enters the cell (+30mV)Repolarization – K+ gates open and K+ leaves
the cell Pumps return everything to RMP (-70mV)