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Neurone membrane and aging. Electrophysiological aspects
INTRODUCTION. The cell membranes are formed of lipids and proteins. Because of their hydrophobic nature, phospholipids separate the intracellular from the extracellular medium. DEVELOPMENT. The extracellular medium is a solution enriched with sodium ions, whilst the intracellular medium is rich in potassium ions. In accordance with the laws of chemistry, the asymmetric distribution of ions causes a small potential difference between the inside and outside of the cell. All the cells of the human body show this small difference in potential of about -60 mV. Another component of the cell membranes are proteins. Some of these –the ion pumps or ATPases– maintain the asymmetric distribution of the ions. Other membrane proteins –the ion channels– permit the selective passage of ions between the intracellular and extracellular media. Electrophysiological techniques (patch clamp) applied at a cellular level allow us to measure the passage of ions across a single molecule. Each ion channel permits the passage of a single ionic species. The cells contain ion channels which are transiently permeable to the ions of sodium, potassium, calcium and chlorine. One of the characteristic properties of neurons is that they are excitable cells. Neuronal excitability depends on the ion channels. The neurons show different electrical behavior during the different phases of life. The changes in the electrical activity of the neurons are determined by the activity of the ion channels and their interaction with the liquid surrounding them.