LECTURE 14*Pay very close attention to the figures in chapter 4-Graded PotentialsThe resting potential exists to be a readily available store of energy-70mVGraded potential- small voltage fluctuationsHyperpolarization- increase in electrical chargeDepolarization- decrease in electrical charge-Postsynaptic PotentialsTwo types of graded potentialsExcitatory Postsynaptic Potentials (EPSPs)- brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to produce an action potential (-50mV)Inhibitory Postsynaptic Potentials (IPSPs)- brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential-Summation of Input PotentialsTemporal Summation- graded potentials that occur at approximately the same time on a membrane are summedSpatial Summation- graded potentials that occur at approximately the same location and time on a membrane are summed-Action PotentialsThreshold Potential- the needed voltage to cause an action potential (-50mV)Action Potentials- brief large reversal in the polarity of an axon’s membraneVoltage-sensitive channels- gated channels that are only open at certain membrane voltagesFigure 4-19Unequal distribution of different ions causes the inside of the axon to be relatively negatively chargedAbsolute Refractory- Period when the neuron cannot fire another action potentialRelative Refractory- Period where another action potential can occur, but would take more depolarization to reach threshold-Refractory PeriodsThis phase is very important because it keeps the signal (action potential) from traveling back up the axon (back propagation)-Myelin SheathGlial CellsSchwann cells-PNSOligodendroglia cells- CNSNodes of Ranvier- gaps between myelinationSaltatory Conduction- propagation of an action potential at successive nodes of RanvierWhat happens during the refractory periods:Na+ in= Na+ channels open, K+ channels closeK+ out= K+ channels open, Na+ channels closePump= 3 Na+ pumped out, 2 K+ pumped inPSYC 260 1st Edition Lecture 14Outline of Last LectureI. Herman von HermholtzII. The Axon and Moving IonsOutline of Current LectureI. Graded PotentialsII. Postsynaptic PotentialsIII. Summation of Input PotentialsIV. Action PotentialsV. Refractory PeriodsVI. Myelin SheathVII. What happens during the refractory periodsCurrent Lecture LECTURE 14 *Pay very close attention to the figures in chapter 4-Graded Potentials - The resting potential exists to be a readily available store of energyo -70mV- Graded potential- small voltage fluctuationso Hyperpolarization- increase in electrical chargeo Depolarization- decrease in electrical charge -Postsynaptic Potentials- Two types of graded potentialso Excitatory Postsynaptic Potentials (EPSPs)- brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to produce an action potential (-50mV)o Inhibitory Postsynaptic Potentials (IPSPs)- brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential -Summation of Input Potentials- Temporal Summation- graded potentials that occur at approximately the same time on a membrane are summed - Spatial Summation- graded potentials that occur at approximately the same locationand time on a membrane are summed -Action Potentials- Threshold Potential- the needed voltage to cause an action potential (-50mV)- Action Potentials- brief large reversal in the polarity of an axon’s membraneo Voltage-sensitive channels- gated channels that are only open at certain membrane voltages- Figure 4-19o Unequal distribution of different ions causes the inside of the axon to be relatively negatively charged- Absolute Refractory- Period when the neuron cannot fire another action potential- Relative Refractory- Period where another action potential can occur, but would take more depolarization to reach threshold  -Refractory Periods- This phase is very important because it keeps the signal (action potential) from traveling back up the axon (back propagation) -Myelin Sheath- Glial Cellso Schwann cells-PNSo Oligodendroglia cells- CNS- Nodes of Ranvier- gaps between myelination - Saltatory Conduction- propagation of an action potential at successive nodes of Ranvier What happens during the refractory periods:- Na+ in= Na+ channels open, K+ channels close- K+ out= K+ channels open, Na+ channels close- Pump= 3 Na+ pumped out, 2 K+ pumped