The Parasympathetic Nervous System

Introduction:
The overall nervous system is made up of the Central Nervous System and the Peripheral Nervous System, with the autonomic nervous system being a division of the peripheral nervous system. The autonomic nervous system regulates glands as well as the smooth and cardiac muscle. There are three separate systems within the autonomic nervous system and are called the sympathetic nervous system, parasympathetic nervous system and the enteric nervous system. They are responsible for the ‘fight or flight’ and ‘rest or digest’ responses. The sympathetic nervous system appears from the spinal cord while the parasympathetic nervous system emerge from the top and bottom segments of the spinal cord. From figure 1 it can be seen that while both
the systems act on the same ograns of the body, they have opposing effects. Both divisions play important roles during and after exercise. Figure 1. Role of the parasympathetic and sympathetic nervous system. http://yogaforhealthyaging.blogspot.in/2015/06/vagal-tone-and-yoga.html Sympathetic nervous system during exercise:
This division of the autonomic nervous system deals with the fight ot flight response. It is to do with activities linked to the release energy. The cell bodies of sympathetic neurons are located in the centre of the spinal cord. This system controls cardiovascular reactions during excerise. During exercise there is increased release of adrenaline and nordadrenaline that causes an increase in heart rate, allowing better circulation of the blood and therefore oxygen and glucose, and an increase in blood sugar, thereby providing more glucose for energy. The sympathetic system (seen in figure 1) also causes increased blood flow to muscles, aiding movement, dilation of the airways, allowing more efficient respiration, stimulation of sweating, and inhibition of the digestive system allowing all energy resources to be directed towards running.
Parasympathetic nervous system during exercise
This division of the autonomic nervous system deals with the ‘rest or digest’ mode.
The parasympathetic nervous system works by taking over the fight or flight responses of the nervous system. It supports activities that are related to storing energy rather than releasing it. These activities include salivation, increased blood flow to the gastrointestinal system and digestion while the sympathetic nervous system inhibits salivation and stimulates glucose release. After exercise the parasympathetic system facilitates an increase in blood flow to the stomach and a decrease in blood flow to the skeletal muscles. There is also an increased production of digestive enzymes that aid the absorption of nutrients. The main neurotransmitter linked to the parasympathetic nervous system is acetycholine, the levels of which rise after exercise and slows down the heart rate as the body is in an inactive
state.
What has research taught us?
Exercising can cause a decrease in one’s stress levels which can further lead to a decrease in the blood pressure levels. In this case the body is at rest and the parasympathetic nervous system is activated. A study was conducted by Nagai et al investigated the autonomic nervous system of both obese and healthy children in relation to how much they exercised. If the children exercised more than thrice a week they were considered as active. If they didn’t exercise at all, they were considered as inactive. The autonomic nervous system was measured while the body was at rest by means of heart rate variability power spectral analysis, which helps to separate the frequency of the heart rate. A low frequency would mean a mixed sympathetic and parasympathetic nervous system activity however a high frequency is mainly linked to the parasympathetic nervous system and total power. Results showed that more active children had a lower resting heart rate and that those children who were obese and active and those who were slender and inactive had similar results in the measurement criteria.
In conclusion, the obese yet active children had less sympathetic and parasympathetic activities as compared to the children who were slender. This reduction may be due to the exercise inactivity of the children. It can be said that running, as an exercise in general can enhance the autonomic nervous system in the active children. The autonomic nervous system adapts its response according to activity level. For example, recreational athletes show sympathetic dominance while professional athletes exhibit parasympathetic dominance.
Hence it can be said that the sympathetic nervous system causes an increase in the heart rate and respiratory rate during exercise in addition to an increase in the levels of adrenaline, in order to faciltate the fight or flight mode. On the other hand the parasympathetic nervous system takes over the sympathetic nervous system after exercising as this is when the body is at
rest.