CHAPTER THREE

Resting Potential

Action Potential

RESTING POTENTIALComposition of the Intracellular and Extracellular Fluids

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Ions

3

RESTING POTENTIALComposition of the Intracellular and Extracellular Fluids

Concentrations of Ions Inside and Outside of Neuron

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RESTING POTENTIALComposition 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.

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RESTING POTENTIALFactors that move molecules

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RESTING POTENTIALComposition of the Intracellular and Extracellular Fluids

Forces Acting on Ions

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RESTING POTENTIALComposition of the Intracellular and Extracellular Fluids

AT THE SYNAPSE (BETWEEN NEURONS)Release of Neurotransmitters

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Excitatory postsynaptic potentials (EPSPs) Produce slight

depolarizations Open sodium

channels

IN THE POST-SYNAPTIC NEURONAfter Neurotransmitters have Interacted with receptors

Inhibitory postsynaptic potentials (IPSPs) Produce slight

hyperpolarizations Open either chloride or

potassium channels

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IN THE POST-SYNAPTIC NEURONAfter Neurotransmitters have Interacted with receptors

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IN THE POST-SYNAPTIC NEURONNeural Integration

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Axon Hillock

ACTION POTENTIALAxon Hillock

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ACTION POTENTIALPictured on An Oscilloscope

ACTION POTENTIALPictured 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.

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ACTION POTENTIALRefractory 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.

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ACTION POTENTIALCharacteristics

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ACTION POTENTIALPropagation of an Action Potential

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ACTION POTENTIALPassive Conduction vs. Saltatory Conduction

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Copyright © 2004 Allyn and Bacon

ACTION POTENTIALPropagation 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

ACTION POTENTIALWhen things go wrong…

NEUROTRANSMITTER DEACTIVATION