Parasympathetic Nervous System ( ESSAY )

Consider your heart for a moment. For the average person at rest, like you probably are, sitting in front of your computer, reading from my blog, the heart beats at around 60 beats/minute. One beat per second. Nice and easy..... But if you were somehow be able to disconnect your heart from your autonomic nervous system, you will certainly guessed that things will change. But, your heart will not stop. Actually, it will be the opposite. Your heart rate will speed up. It will start to beat at around 100 beats/minute, 2/3 faster, and that is just at rest, without you breaking a single sweat. But your cardiac muscle would experience a lot of "wear and tear". The surrounding blood pressure would be under enormous pressure, and your body will suddenly require - and waste - a lot of energy. Basically your homeostasis - the name for when your body is in balance - would be ruined. Partly, the job of the parasympathetic nervous system is to keep your heart under homeostasis, or in balance. It's often described as the calming side, the mellow side of your autonomic nervous system, a kind of antidote to the effects of stress created by your sympathetic nervous system. But it's job is really much more than that. Unlike your sympathetic division, which deals with the "crisis of now", which is not a movie, by the way, the parasympathetic division deals with, well, everything else. It not only calms you down after being stressed out, but also it allows you to digest food, to reproduce, to excrete waste, to fight off infection, well everything other than becoming stressed, all the things you need to do to, well, be a living thing and live. But our bodies can only do that when they are in balance, somewhere between excitement and inhibition, both aroused enough but also calm enough, then your body can do the business of living. Our sympathetic and parasympathetic nervous system differ not only by their functions, but also by their positions and the positions of their ganglia. The sympathetic ganglia are located near the spinal cord, while the parasympathetic ganglia are found way out, or even in the effector organs. Likewise, the use of neurotransmitter in the two system are similar, but not exactly the same. In both system, the neurons release acetylcholine, in the preganglionic cell, which is the cell that comes before the ganglia. But the difference here is what comes after the acetylcholine crosses the ganglia. In the parasympathetic division, what comes out of the ganglia is still acetylcholine, while what comes out of the sympathetic division is norepinephrine. But, the biggest anatomical difference between these two system has to do with the physical networks that they form as they reach to every part of your body. The network of your sympathetic division -- I'm getting tired of spelling s-y-m-p-a-t-h-e-t-I-c and p-a-r-a-s-y-m-p-a-t-h-e-t-I-c all the time -- is found in the thoracolumbar area of your spinal cord. While the parasympathetic division are craniosacral, meaning they sprout from the bottom of your brain and just superior to your tailbone, and most of these nerves never go through your spinal cord.
Most of you will think that the two divisions of your autonomic nervous system as opposites or rivals, but that is a little off the mark. Looking at your body as a whole, you should picture them as two side of a scale. Sometimes your body tips a little to one side, and sometimes your body tips to the other side. The balance depends on having the right amount of both. The rate of action potentials travelling through your sympathetic division is known as your "sympathetic tone" and the tone travelling through your parasympathetic system is "parasympathetic tone". And most of the time, your parasympathetic tone is actually dominant, something I'm very glad to know.