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Neuroscience (289)
NROB60H3 (151)
Chapter 4

Chapter 4 Notes

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Janelle Leboutillier

Chapter 4 Notes Action Potential: Conveys information over distances in the nervous system - Often called a spike, nerve impulse, or a discharge - Frequency and pattern of action potentials constitute the code used by neurons to transfer information from one location to another Four Components to An Action Potential Rising Phase: Characterized by a rapid depolarization of the membrane; continues to peak until Vm reaches 40 mV Overshoot: Phases where inside of the neuron is positively charged with respect to the outside Falling Phase: Rapid repolarization until the membrane is actually more negative than the resting potential UndershootAfter-Hyperpolarization: Gradual restoration of the resting potential Generation of Action Potential - Perception of sharp pain when a thumbtack enters your foot is caused by the generation of action potentials in certain nerve fibers in the skin o Chain of events: Thumbtack enters skin Membrane of nerve fibers is stretched (Causes activation of specialized ion channels sensitive to membrane stretching) Na+ - permeable channels open; depolarizes membrane beyond threshold - Applying increasing depolarization to a neuron has no effect until it crosses threshold; therefore APs are all-or-none Generation of Multiple Action Potentials - Action potentials in succession can be generated by passing continuous depolarizing current into a neuron - Rate of action potential generation depends on the magnitudeintensity of the continuous depolarization current - Firing frequency of action potentials reflects the magnitude of the depolarizing current o Stimulus intensity is coded this way in NS o There is a limit to rate at which neuron can generate AP (1000Hz) - Absolute Refractory Period: It is impossible to initiate another AP for about 1msec after an AP has been initiated - Relative Refractory Period: The amount of current required to depolarize the neuron to action potential threshold is elevated above normal The Action Potential Membrane Currents and Conductances Neuron consists of 3 protein molecules: - Sodium-potassium pump Works continuously to establish and maintain concentration gradients - Sodium channels - Potassium channels - K+ is concentrated 20-fold inside the cell, Ek = -80mV www.notesolution.com
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