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NROB60H3 (151)
Chapter 4

Chapter 4: The Action Potential

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Janelle Leboutillier

Chapter 4The Action Potential Introduction o Action potential rapid reverse of the negatively charged cytosol such that it becomes positively charged with respect to the outside aka spike nerve impulse dischargeAll have same size and duration frequency and pattern emit information Properties of the Action PotentialThe Ups and Downs of an Action Potential o Resting membrane potential 65mV o Oscilloscope used to study action potentials measures voltage changes over time o Rising phase rapid depolarization of membrane Vm peak 40mV o Overshoot part of action potential where the inside iscompared too Falling phase rapid repolarization until membrane is actually more negative than resting potential o Undershootafterhyperpolarization last part of falling phase o Then there is a gradual restoration of the resting potential The Generation of an Action Potential o Depolarizationgenerator potential the depolarization due to incoming Na from opening of Na channels and electrochemical gradientCan be due to channels sensitive to membrane stretching neurotransmittersinjecting electrical current o Threshold the critic level of depolarization that must be crossed to generate an action potential The Generation of Multiple Action Potentials o Firing frequency Rate of action potential generation depends on the magnitude of the continuous depolarizing current One way stimulus intensity is encodedMaximum firing frequency 1000 Hz Absolute refractory period 1ms the period of time after an initial action potential is generated during which it is impossible to generate another oneRelative refractory period several ms after end of absolute refractory period where amount of current required to depolarize the neuron to action potential threshold is above normal Methods of Recording Action Potentials o Intracellular required impaling of the neuron or axon with a microelectrode filled with salt solution KCl connected to amplifier that find difference in potential and displayed on an oscilloscope o Extracellular electrode fine glass capillary with salt solution or thin insulated metal wired is placed near the membrane and measured compared to the ground changes can be seen with oscilloscope or connecting amplifier to loudspeaker which shows impulses as pop noises The Action Potential in TheoryMembrane Currents and Conductance o K concentrated 20x inside Na concentrated 10x outside o Ek 80mV Ena 62mV
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