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The Action Potential
Four Signals Within the Neuron
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Input signal – occurs at sensor or at points
where dendrites are touched by other neurons.
Integration (trigger) signal – occurs at first
node (in sensory neuron) or at axon hillock.
Conducting signal – travels down axon.
Output signal – releases neurotransmitter at
axon terminal.
These signals are changes in the resting state.
The Neuron at Rest
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Neurons have potassium (K+) inside and
sodium (Na+) outside in the extracellular
fluid.
Ion channels in the cell wall (membrane) are
selectively permeable to potassium, sodium or
calcium.
Ion pumps maintain the cell’s inner
environment.
How Ions Cross the Membrane
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Diffusion – an ionic concentration gradient
exists
Differences in electrical membrane potential
and equilibrium potential
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Ionic driving force
Ion pumps
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Sodium/potassium, calcium
Resting Potential
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Membrane potential is voltage across the
neuronal membrane.
Resting potential is the point at which all of
the forces acting upon ions are in balance
(equilibrium).
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Diffusional and electrical forces are equal.
Vm = -65 mV
Tutorial on Action Potential
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http://psych.hanover.edu/Krantz/neural/action
potential.html
The Action Potential
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Depolarization – influx of sodium (Na+) or another
positive ion makes the membrane potential more
positive.
When the membrane potential reaches threshold,
voltage-gated Na+ ion channels open.
After 1 msec, voltage-gated K+ channels open,
polarizing the neuron again.
Sodium-potassium pump helps restore neuron to its
resting potential.
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Resting potential is polarized, typically -65 mV