We explain the differences between these two opposing nervous systems.
The nervous system is responsible for controlling the body. The nerve center of the central nervous system is the brain, which together with the spinal cord and the rest of the body’s nerves, is responsible for sending and receiving signals to regulate the activity of the organism.
When we make our limbs move, we are using the central nervous system, which is primarily responsible for our conscious functions. But our nervous system takes care of many bodily tasks without us being aware of it . We call the responsible autonomic nervous system, the nervous system that acts outside of our will or consciousness.
In this article we will talk about an important part of the autonomic nervous system, a team of two antagonistic nervous systems (with opposite functions). These are the sympathetic nervous system and the parasympathetic nervous system .
Autonomic nervous system
The functions of the autonomic nervous system are mostly performed away from the brain. This system basically acts through nerves in the spinal cord and those nerves that surround and control our viscera, collecting information from them and sending them orders when necessary.
The autonomic nervous system is responsible for tasks such as :
- The digestion
- The breathing
- erection and ejaculation
- involuntary muscle movements
And many more. Basically our autonomic nervous system is in charge of bodily functions of which we have no control or awareness, maintaining the balance (homeostasis) of the body and adapting to our needs, for example those that derive from our emotional state.
This autonomic nervous system has two main subdivisions, which are responsible for performing antagonistic functions: The sympathetic and parasympathetic nervous systems . Below we present them together with their main functions, so that we can observe the differences between both systems.
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sympathetic nervous system
It is the part of the nervous system that is responsible for activating functions of the organism. Its main task is to initiate the response known in English as “fight or flight” . Although this response is initiated only when necessary in healthy people, the sympathetic nervous system is constantly active to keep the body’s functions in balance.
This sympathetic nervous system is rapidly activated in preparation for situations that require frantic activity, alertness, or the use of force . This means that situations that provoke strong emotions in us such as fear, anger or shame will initiate sympathetic activity.
This fight or flight response is translated, thanks to the sympathetic system, into an increase in heart rate, the dilation of the bronchi (to improve our oxygen uptake) and the widening of the blood vessels that irrigate the skeletal muscles and the heart , in preparation for an episode of intense physical activity.
In addition, the production of adrenaline and noradrenaline by the adrenal glands is stimulated, accelerating our metabolism and producing different effects on the organs, which will be opposite to the effects associated with the parasympathetic system and will be discussed later in the article.
At the structural level, the sympathetic system is made up of two types of neurons, preganglionic and postganglionic . Preganglionic neurons are those that leave the thoracolumbar area of the spinal cord reaching the ganglia, neuronal clusters that communicate with the other type of neurons of the sympathetic system, the postganglionic ones.
The signals that go from the spinal cord to the rest of the body reach the ganglia through the preganglionic neurons, where they release acetylcholine, a neurotransmitter that will activate the postganglionic neurons, which extend to the rest of the body, which in turn will be the responsible for releasing norepinephrine, which will produce the effects associated with the sympathetic system in peripheral tissues .
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parasympathetic nervous system
The parasympathetic nervous system is also considered part of the autonomic nervous system, even though its nerves are communicating directly with the central nervous system. It also exhibits the structure of pre/postganglionic neurons, much like the sympathetic nervous system, although they are located from cranium to sacrum rather than in the thoracolumbar region.
The functions carried out by the parasympathetic nervous system are opposite to those of the sympathetic nervous system , and it is this constant opposition of negative and positive effects that generates a balance in bodily functions, the so-called homeostasis .
When the parasympathetic nervous system is activated, it favors the reactions of feeding and reproduction, in addition to those of rest and digestion . These functions are directly opposite to those of the parasympathetic system and are downregulated when it is necessary to activate the “fight or flight” response.
Put another way, if the sympathetic system upsets us, the parasympathetic system calms us down and urges us to eat, rest, and reproduce . These are activities that cannot be performed safely under very stressful conditions, in which the sympathetic system acts, so its activation implies the inhibition of the other system, and vice versa.
This is already happening because our body, among other things, will give more blood to the system that needs to act as a priority, taking resources away from the antagonistic system, so that the effects of a system are stronger for a while and do not obstruct each other. they.
Functional differences between sympathetic and parasympathetic system
To better exemplify the differences in functions of these antagonistic systems, we are going to list some specific functions on which both act, clarifying their different effects . In general, we could say that:
- The sympathetic system is responsible for accelerating our bodily functions, preparing us for action and stress.
- The parasympathetic system is responsible for slowing down our body and metabolic activity, preparing us for periods of rest and tranquility.
1. Effects on the eye
The sympathetic nervous system will dilate our pupils , allowing us to better detect movement and preparing us for a violent encounter.
The parasympathetic system will be in charge of contracting our pupils, returning us to normality . This is the general dynamic of the relationship between both systems.
2. Effects on the digestive system
The sympathetic system will prevent the peristaltic movements of the intestines and redirect blood flow to the muscles, which need more blood at times of action.
The parasympathetic system will ensure that our digestive activity is promoted, activating salivation and other processes of the digestive system and slowing down the inhibitory effects of the sympathetic system.
3. Effects on circulatory system
The sympathetic system will be responsible for accelerating our heart rate , widening our bronchial tubes so that we have a higher concentration of oxygen in the blood, while expanding the diameter of our veins and arteries so that the blood reaches more easily the remote areas of the body. .
The parasympathetic system will be in charge of doing the exact opposite, slowing down the heart rate, reducing respiratory capacity and reversing the vasodilator effects of the sympathetic system, so that we can rest easy and spend less energy.
4. Effects on the excretory system
When the sympathetic system is activated, the last thing it needs is excretory activities taking place at that time (after all, we need to fight or flee!). It relaxes the sphincter of the bladder, which is why there are people who urinate when they go through panic processes, but contract the anal sphincter to avoid defecation .
As we can imagine by now, the parasympathetic nervous system will relax our anal sphincter but contract the bladder sphincter.
5. Effects on the reproductive system
In the reproductive system, especially the male, the opposite effect occurs. As we have said, the sympathetic system is responsible for activating the body, but when it comes to sexual activity, the sympathetic system avoids it, by vasoconstricting the circulatory system that fills the penis with blood . This prevents us from getting boners while running away or fighting, which is appreciated.
The parasympathetic system will be responsible for increasing blood flow to the genitals in response to sexual arousal . Ejaculation, on the other hand, is also the result of the sympathetic activity of the nervous system, putting an end to male genital activity.
Bibliographic references
- Drake, Richard L.; Vogl, Wayne; Mitchell, Adam WM, eds. (2005). Gray’s Anatomy for Students (1 ed.). Elsevier. pp. 76–84
- McCorry LK (2007). Physiology of the autonomic nervous system. American journal of pharmaceutical education, 71(4), 78.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.