Electricity and the brain

Part 1 of 3 : Ions

Most people know that the brain uses electricity to operate. However, what most people do not realize is that the electricity produced by the brain is different from the one produced by batteries or the companies that provide electricity to your home. Indeed, the source of electricity in these examples comes from chemical reactions or from natural resources. This electricity is then routed to your house, for your use, by transfer of electrons between metal atoms that make up the electrical wiring. We can thus define electricity as a movement of electric charges between a potential difference or voltage. However, the brain uses a slightly different system to generate and propagate electricity. Some basic concepts are needed before we can understand how brain cells (neurons) generate electricity in their cell body and propagate it along their axons (Figure 1).

Matter can be divided into basic elements called atoms. Calcium, sodium, potassium and chlorine are examples of atoms. Table salt contains mostly sodium chloride, that is a sodium (Na) and a chloride (Cl) atom. If the two atoms are to be held together, each atom carries a charge (sodium has a positive charge and chloride has a negative charge). Since each atom has an opposite charge, they attract each other, much like the poles of two magnets. However, the forces that attract these two atoms are weak so that when you put the salt in an aquarium filled with water (Figure 2), atoms dissociate to form ions, a positively charged sodium (Na +) and a negatively charged chloride (Cl-). The atoms then diffuse so as to be uniformly distributed in the aquarium. It must be noted that although the atoms of the salt are dissociated and they are charged, the aquarium is electrically neutral (as much positive charges as negative charges).

Adding other specific components in this tank (potassium chloride (K + and Cl-), magnesium chloride (Mg 2 + and 2Cl-), glucose (sugar), calcium chloride (2Cl- and Ca2 +), sodium bicarbonate (Na + and HOCOO-), proteins and oxygen) will result in a uniform distribution of these constituents in the aquarium. We then get a liquid that roughly reconstitutes the fluid that neurons bathe in (cerebral-spinal fluid).

Eric Trudel