The second theory to be born was the
ionic theory. It makes it possible to explain the *electric* phenomena observed. The neuron maintains
ion flows. These flows are perceived by our
electricals appliance like potential differences. Flows observed, are under the
dependence of ionic channels, genuine molecular pumps.
The ionic channels discovered, are
sensitive to only one type of ion:
- The channels Na transport sodium ions.
- The channels K transport potassium.
- The channels Ca, calcium.
- The channels Cl, chlorine.
We know that there exists, still,
channels of which we are unaware of function and sensitivity.
Some are fast, the other slow ones,
for the same type of transported ion.
Some channels are known as *voltage dependent*, they can, in experiments, being controled by an electrical
current. Others are sensitive to chemical molecules or to pressure. The
knowledge of these sensitivities will make it possible to find more effective
drugs and treatments.
The propagated response drive a
significant flow of ions, on both sides of the neuron membrane. It is a
short, but relatively slow phenomenon. The *electric* spike observed, is the
observation of this ionic phenomenon, with misfits means.
The rest potential is a
maintained ionic imbalance. This imbalance makes it possible, to improve the
response time of the neuron.
The neuron is not an electric cell.
It is an alive entity and transmitted information is of biochemical nature
(neurotransmitters). The neuron is a communication cell. The electric
observations are the fact of unsuited, but practical apparatuses. To measure the
ion flows is not an easy spot. It is for that that we convert them into
potentials. It is not for that that *electric* potentials exist:
- It there not short-circuit in a nerve.
- The speed transmission is not that of
electricity.
- It there not of propagation to the close neuron.
- The transmission of the spike, with the following
neuron, is of biochemical nature.
- There is not electric circuit between the
interior of the cell and the extracellular medium. It there not *electric*
battery
effect.
- There are only differences in
ionic concentrations maintained by molecular pumps.
