Читать книгу Neurobiology For Dummies - Frank Amthor - Страница 75

What is osmotic pressure, and why does it matter to cells? Well, you’ve probably heard the classic lines, “Water, water, everywhere; nor any drop to drink.” Consider how people stranded in the middle of the ocean can’t survive by drinking the seawater all around them. High concentrations of salts (primarily sodium chloride) are dissolved in seawater. If seawater is added to the already highly concentrated extracellular fluid around our cells, the result is that water will tend to move from the higher concentration inside our cells to the lower concentration (relative to the concentration of ions) outside.

The plasma membranes of cells are not totally impermeable to water, because, among other reasons, membranes have water-permeable channels called aquaporins. This causes a net loss of water inside our cells so that they become hyperconcentrated with ions and die. Neurons, like other cells, have a variety of mechanisms for dealing with concentration balances between their cytoplasm and the extracellular fluid.