PSYA01H3 Chapter Notes - Chapter 3: Alan Lloyd Hodgkin, Andrew Huxley, Aa Battery

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12 Aug 2016
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THE ELECTROCHEMICAL ACTIONS OF NEURONS – INFORMATION
PROCESSING
The communication of information within and between neurons proceeds in two stages:
1. Conduction – conduction of an electric signal over relatively long distances within
neurons, from the dendrites, to the cell body, then throughout the axon
2. Transmission – transmission of electric signals between neurons over the synapse
Together, these stages are what scientists generally refer to as the electrochemical action of
neurons.
Electric signaling – conducting information within a neuron
Recall: Cell membrane is porous and allows small electrically charged molecules, called ions, to
flow into and out of the cell
The flow of molecules across a cell membrane enhances the transmission of information in the
nervous system
The resting potential – the origin of the neuron’s electrical properties
Resting potential – the difference in electrical charge between the inside and outside of a
neuron’s cell membrane
oNeuron’s natural electric charge
oCreates the environment for a possible electrical impulse
o1st discovered in 1930s; back then it was measured to be -70 mV (millivolts) [roughly
1/200 of the charge of an AA battery]
oArises from the difference in concentrations of ions inside and outside the neuron’s cell
membrane
oIn resting state: (natural)
High concentration of K+ and A- (negatively charged protein ions) inside the
neuron’s cell membrane
High concentration of Na+ and Cl- outside the neuron’s cell membrane
oDifferences in K+ concentration are the basis of the resting potential
oThe concentration of K+ inside and outside an axon is controlled by channels in the axon
membrane that allow molecules to flow in and out of the neuron
oResting state – the channels that allow K+ molecules to flow freely across the cell
membrane are open, while channels that allow the flow of Na+ and the other ions noted
earlier are generally closed. Because there is a naturally higher concentration of K+
molecules inside the neuron, some K+ molecules move out of the neuron through the
open channels, leaving the inside of the neuron with a charge of about −70 millivolts
relative to the outside.
Discovery of the resting potential (1939)Alan Hodgkin and Andrew Huxley experimented
with a squid’s giant axon as it is 100 times larger than the biggest axon in humans. They inserted
a thin wire into the squid axon and placed another wire just outside the axon. They found a
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