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1 Introduction

“resting” potential is built up again, so that the neuron can be ready for the next piece

of information or action potential. Only two ion channels are part of this process, the

sodium channel that releases the potential and the potassium channel that builds it up

again. This readiness of each neuron is a high-energy process, which is why the brain

uses 70 % of the energy available to the body.

How do these ion channels work? Here is the example of the voltage-gated sodium

channel, i. e., the channel that only lets sodium through, but even that only when the

membrane potential suddenly changes at the part of the protein that senses voltage

(Figure 1.37). Most ion channels have several transmembrane peptide helixes, in this

case six helixes together form one subunit, and four subunits together form the chan-

nel. The structures in between the subunits fold onto the channel opening; with that the

channel is generally closed. One of those sites has a lot of charged amino acids on the out-

side, which constitute the voltage sensor (Figure 1.37). With a change in voltage comes a

change in charge, which changes the three-dimensional structure of the voltage senor.

The movement of one section initiates the change in structure of the units that block the

channel, thus opening it. The opening of the channel equalizes the sodium concentration

on each side, thus starting the action potential.

Figure 1.37: How a “voltage-gated” ion channel

works. Basically, the channel is normally closed.

When the voltage sensor senses a change in the

amount of ions, the barriers move away and the

channel opens.