~bn11 action potential.ppt
TRANSCRIPT
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NeuralCommunication
Action Potential
Lecture 11
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Action Potentials Large and rapid change in membrane
potential electrically-gated channels EPSPs
threshold potential Occurs in axon
triggered at axon hillock ~
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AP Characteristics
Voltage-gated channels All or none Slow Non-decremental Self Propagated
regenerated ~
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-70
-60
0
+40
-80
Time
Vm
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-70
-60
0
+40
-80
Time
Vm
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-70
-60
0
+40
-80
Time
Depolarization
Na+ influx
C & E gradientsdrive Na+ into cell
Vm
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-70
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0
+40
-80
Time
Repolarization
K+ efflux Vm
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-70
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0
+40
-80
Time
After- hyperpolarization
Vm
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Refractory Period
after AP won’t fire again relative & absolute
Relative during after hyperpolarization requires greater depolarization ~
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Relative Refractory Period
-70
-60
0
+40
-80
Time
Vm
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Absolute refractory period
Na+ channels deactivate will not trigger AP must reset
Ball & Chain Model ~
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Na+ channel deactivation
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Na+ channel deactivation
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Frequency Code
Pattern = Intensity of stimulus frequency of APs
Place = type of stimulus Visual, auditory, pain, etc. Brain area that receives signal Doctrine of Specific Nerve Energies ~
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FREQUENCY CODE
1.
2.
3.
Weak stimulus
Moderate stimulus
Strong stimulus
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Saltatory Conduction
Myelinated neurons oligodendroglia & Schwann cells
Transmit long distances APs relatively slow, regenerates EPSPs - fast, decremental
Saltatory: combines both types of current speed without loss of signal ~
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Saltatory Conduction Nodes of Ranvier
action potentials Myelinated
like electricity through wire decremental but triggers AP at next node
Safety factor - trigger AP across 5 nodes .2 - 2 mm apart
larger neurons farther apart ~
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Saltatory Conduction
Nodes of Ranvier
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PSPs vs APs
GradedSummation
longer duration*10-100 msec
chemical-gated passive spread
instantaneousdecremental
All-or-none
short1-2 msec
voltage-gated propagated
slownondecremental