The Action Potential

CHAPTER FOUR

The Action Potential

INTRODUCTION PROPERTIES OF THE ACTION POTENTIAL The Ups and Downs of an Action Potential BOX Four point one BRAIN FOOD: Methods of Recording Action Potentials The Generation of an Action Potential The Generation of Multiple Action Potentials Optogenetics: Controlling Neural Activity with Light BOX Four point two PATH OF DISCOVERY: The Discovery of the Channelrhodopsins, by Georg Nagel

ACTION POTENTIALS, AXONS, AND DENDRITES BOX Four point six OF SPECIAL INTEREST: The Eclectic Electric Behavior of Neurons CONCLUDING REMARKS

INTRODUCTION

Now we come to the signal that conveys information over distances in the nervous system-the action potential. As we saw in Chapter Three, the inside of the neuronal membrane at rest is negatively charged in relation to the outside. The action potential is a rapid reversal of this situation such that, for an instant, the inside of the membrane becomes positively charged in relation to the outside. The action potential is also often called a spike, a nerve impulse, or a discharge.

The action potentials generated by a patch of membrane are all similar in size and duration, and they do not diminish as they are conducted down the axon. Keep in mind the big picture: The frequency and pattern of action potentials constitute the code used by neurons to transfer information from one location to another. In this chapter, we discuss the mechanisms that are responsible for the action potential and how it propagates down the axonal membrane.