PSIO 5th Edition Lecture 34 Outline of Last Lecture Neurophysiology The Resting Potential Outline of Current Lecture I Neurophysiology The Action Potential II Graded Potentials III Depolarization IV Refractory Periods Current Lecture 1 2 3 4 List in order the principal events associated with an action potential Define the phrase all or none in the context of the neuronal action potential Compare and contrast the characteristics of graded vs action potentials Discuss the basis of absolute and relative refractory periods Neuronal Action Potential A Neurons are excitable cells Can change membrane potential to generate and electrical signal B Principal Mechanism Voltage gated Na channel Chain of Events in the Generation of the Action Potential 1 Local change in membrane potential such local changes can be hyperpolarizing more negative or depolarizing less negative an Action Potential begins with a local depolarization Graded Potentials occur in dendrites and cell body of neuron size varies with strength of stimulus usually generated by chemically and mechanically gated channels Two Types Inhibitory Post Synaptic Potentials IPSP and Excitatory Post Synaptic Potentials EPSP 2 Depolarization to a threshold value indices a population of voltage gated Na channels within the local region of membrane to open 3 Critical Point shortly after Na Channels open they spontaneously close inactivation 4 Depolarization also opens more slowly a second population of channels Voltage gated K channels Refractory Periods periods during which it is difficult or impossible to generate a second AP 1 Absolute Refractory Period immediately following inactivation of Na channels membrane cannot be restimulated to produce AP involves resetting of Na channels 2 Relative Refractory Period a period during which a new AP can be produces but it takes a larger than normal stimulation involved resetting of K channels Importance of Refractory Periods 1 Estabilishing maximum rate of Action Potentials 2 Influence the characteristics of AP propagation forward propagation from axon hillock to axon terminal
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