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The Action Potential

The Action Potential. Four Signals Within the Neuron. 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.

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The Action Potential

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  1. The Action Potential

  2. Four Signals Within the Neuron • 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.

  3. The Neuron at Rest • 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.

  4. How Ions Cross the Membrane • Diffusion – an ionic concentration gradient exists • Differences in electrical membrane potential and equilibrium potential • Ionic driving force • Ion pumps • Sodium/potassium, calcium

  5. Resting Potential • 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). • Diffusional and electrical forces are equal. • Vm = -65 mV

  6. Tutorial on Action Potential • http://psych.hanover.edu/Krantz/neural/actionpotential.html

  7. The Action Potential • 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. • Resting potential is polarized, typically -65 mV

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