4 Forces Behind Resting Potential Selective Permeability- some molecules pass through membrane more freely than others; ion channelsSodium-Potassium Pump transports 3 Na out of, 2 K into cellResult:Concentration GradientElectrical Gradient
13 Figure 2.20 Saltatory conduction in a myelinated axon An action potential at the node triggers flow of current to the next node, where the membrane regenerates the action potential.
14 The Action Potential The RefractoryPeriod Absolute Refractory Period Sodium gates are firmly closedMembrane cannot produce AP, regardless of the stimulation.Relative Refractory PeriodSodium gates in usual state, but the potassium gates remain open.Stronger than normal stimulus needed for action potential.
15 Propagation of the Action Potential From: Axon HillockTo: Terminal ButtonsAP travels in one direction only. WHY?
16 The Myelin Sheath and Saltatory Conduction Myelin Sheaths increase the speed of neural transmissionNodes of Ranvier-Short area’s of the axon that are unmyelinatedSaltatory Conduction-jumping action of actions potentials from node of Ranvier to node of Ranvier
18 Signaling Without Action Potentials Depolarizations and hyperpolarizations of dendrites and cell bodiesSmall Local neurons-produce graded potentials (membrane potentials that vary in magnitude and do not follow the all-or-none law)