C HAPTER T HREE Resting Potential Action Potential

R ESTING P OTENTIAL Composition of the Intracellular and Extracellular Fluids 2 Ions

3 R ESTING P OTENTIAL Composition of the Intracellular and Extracellular Fluids Concentrations of Ions Inside and Outside of Neuron

4 R ESTING P OTENTIAL Composition of the Intracellular and Extracellular Fluids Measuring Charge Inside and Outside of Neuron

Electrical force: charged molecules will be attracted to areas of opposite charge and repelled by areas of like charge. Diffusion: molecules will move from areas of high concentration to areas of low concentration. 5 R ESTING P OTENTIAL Factors that move molecules

6 R ESTING P OTENTIAL Composition of the Intracellular and Extracellular Fluids Forces Acting on Ions

7 Copyright © 2004 Allyn and Bacon R ESTING P OTENTIAL Composition of the Intracellular and Extracellular Fluids

A T THE S YNAPSE ( BETWEEN NEURONS ) Release of Neurotransmitters

9 Excitatory postsynaptic potentials (EPSPs) Produce slight depolarizations Open sodium channels I N THE P OST -S YNAPTIC N EURON After Neurotransmitters have Interacted with receptors

Inhibitory postsynaptic potentials (IPSPs) Produce slight hyperpolarizations Open either chloride or potassium channels 10 I N THE P OST -S YNAPTIC N EURON After Neurotransmitters have Interacted with receptors

11 I N THE P OST -S YNAPTIC N EURON Neural Integration

12 Copyright © 2004 Allyn and Bacon Axon Hillock A CTION P OTENTIAL Axon Hillock

13 A CTION P OTENTIAL Pictured on An Oscilloscope

A CTION P OTENTIAL Pictured on An Oscilloscope

Absolute refractory period: production of a subsequent action potential is extremely unlikely or impossible. Relative refractory period: production of a subsequent action potential is possible in response to larger than normal stimulation. 15 A CTION P OTENTIAL Refractory Periods

When a cell is depolarized to threshold, an action potential is produced. Action potentials are all-or-none. Size and shape are always the same. An action potential either occurs or does not occur. The opening of sodium channels and potassium channels in the neural membrane accounts for the rise and fall seen in a recording of an action potential. 16 A CTION P OTENTIAL Characteristics

17 Copyright © 2004 Allyn and Bacon A CTION P OTENTIAL Propagation of an Action Potential

18 A CTION P OTENTIAL Passive Conduction vs. Saltatory Conduction

19 Copyright © 2004 Allyn and Bacon A CTION P OTENTIAL Propagation inside of a myelin sheath

Puffer fish (fugu) is a dangerous delicacy. Puffer fish produce tetrodotoxin, which blocks sodium channels on the outside surface of the cell membrane. When sodium can ’ t move into the cell, signaling stops. 20 © Jeffrey L. Rotman/CORBIS A CTION P OTENTIAL When things go wrong…

N EUROTRANSMITTER D EACTIVATION