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. V m = -65 mV

6. Tutorial on Action Potential  http://psych.hanover.edu/Krantz/neural/action potential.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