As promised a month ago, today’s post is going to be about how a neuron sends and receives messages. When I sat through this lecture last semester, I was awed by this whole process. You want to talk about a miracle? Look no further than the brain, people. It is so amazing.
So, to begin with you have to reach back to your knowledge of basic physics and remember that things like to flow along a gradient moving from areas of high pressure to areas of low pressure. Stuff just likes to spread itself out and if it has the opportunity to go some place where it can spread out its arms and not touch its neighbor, it will.
Cells in general and neurons in particular have two kinds of channels in their membranes. Passive channels that are open all the time and that allow certain kinds of molecules to freely move into or out of a cell and gated channels which have to be triggered to open or close but that also allow certain kinds of molecules into or out of the cell. The things that the neurons seems to move around a lot are molecules of sodium (Na+), Chlorine (Cl-), Potassium (K+) and Calcium (Ca++).
A neuron is typically negatively charged, around 70 mV. It keeps its negative charge by using the NA/K-ATPase pump. This is also in the cell membrane and its function is to bring in 2 K+ and to push out 3 Na+ was that the cell stays negative. (Keeping in mind that these molecules are trying to move along concentration gradients anyway moving from areas of high concentration to areas of low concentration.)
When a cell receives an incoming neurotransmitter, it will open up its gates and other molecules will flood in and out. When this happens, the voltage will change from negative to positive. But, the cell doesn’t want to be positive, so it has pumps that make it negative again. This swinging from negative to positive is called an action potential. And, it is just so cool. Tune in next week for further discussion of neurons and their parts.
