Introduction To Action Potential Physiology page 1 Introduction To Action Potential About words first. We have action movies, action heroes, action auctions… Whatever the word “potential” refers to, why “action”? Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Content Terminology What action potential really means Where we can find it Neurones Networks of neurones Processing of information Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Action potential definition A temporary reversal in the potential difference across a plasma membrane that occurs when a cell has been activated by a stimulus. This explains the word “action”. Now, what kind of potential is it? Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential U = m x g x h The potential we are talking about is a ‘potential energy’. Potential energy = potential to deliver work Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Tsunami Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential = 1.5 V ~ 220 V U = Q1 x Q2 / r U … voltage It’s an electric potential or voltage. When the battery is strong, it can be compared to a large dam. It has a potential energy ready to be delivered and generate work (that we can measure). Q1 … charge Q2 … charge r … distance Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Electric potential is a voltage that we measure with a voltmeter. … that we measure with a voltmeter. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Electric potential is a voltage that we measure with a voltmeter. It doesn’t matter whether we measure on a battery or neurone. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Electric potential is a voltage that we measure with a voltmeter. It doesn’t matter whether we measure on a battery or neurone. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Electric current is a movement of free electrons. … that we measure with a voltmeter. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Ions exert force on free electrons which move the voltmeter pointer. Ions: anion, cation, onion. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential - + Measuring electric potential is only one way of looking at the complex mechanism. Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential So, under “action potential”, remember the whole mechanism rather than the movement of a voltmeter pointer. Better even, remember everything!  Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Where can we see action potential? Neurones Pacemaker cells In its resting state, a neuron is polarized, with its inside at about -70mV relative to its surroundings. When an excitatory neurotransmitter is released by the presynaptic neuron and binds to the postsynaptic dendritic spines, ligand-gated ion channels open, allowing sodium ions to enter the cell. This may make the postsynaptic membrane depolarized (less negative). This depolarization will travel towards the axon hillock, diminishing exponentially with time and distance. If several such events occur in a short time, the axon hillock may become sufficiently depolarized for the voltage-gated sodium channels to open. This initiates an action potential that then propagates down the axon. Neuromuscular junction Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Action potential Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Conduction in myelinated vs. non-myel. neurones 10 – 120 m/s 5 - 25 m/s Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Saltatory conduction Saltatory conduction is the mechanism by which signals move more quickly in myelinated neurons * Metaphor: Cars (signals) move faster even with fewer lanes (smaller fibers) in the express lane (saltatory conduction) o less merging o still need to fill up car at a gas station Key points to this metaphor, it is the less frequent merging that allows the cars to move faster, in those long stretches where there are no on-ramps (ion channels), there is no exchange of charges leaving the cars free to just shoot quickly to the next on-ramp. But there are some on-ramps (nodes of ranvier) that allow an influx of cars that have full tanks of gas (amplification/depolarization of membrane). Without these periodic gas stations, the cars would run out of gas (the signal would decay away too much to trigger depolarization at the next section with ion channels). Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential 5 m 18 m Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Synaptic transmission Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad

Introduction To Action Potential Physiology page 2 Introduction To Action Potential Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2010 Ludek Nerad