Autonomous nervous system: structures and functions

Throughout our life, we have performed many actions. Let’s run, jump, talk …

All of these acts are voluntary elements that we do voluntarily. But also we do a lot of things that we are not only aware of, many of which are actually the ones that keep us alive and with the opportunity to volunteer, such as controlling heart and respiratory rates, speeding up or decelerating physiological systems, or digestion.

At the neurological level, these two types of actions are carried out by two different systems, the conscious actions being carried out by the somatic nervous system. and the unconscious by the autonomic nervous system.

    What is the vegetative nervous system?

    The autonomic nervous system, also called the vegetative nervous system, is one of the two divisions that have been made of the nervous system at the functional level. this system is responsible for connecting neurons in the central nervous system with those of other systems and organs in the body, Part of the central and peripheral nervous systems. Its basic function is the control of the internal processes of the organism, that is to say of the viscera, being the processes governed by this system of others at our will.

    The connections with the various target organs of this system are both motor and sensitive, having both efferents and afferents. So it is a system that sends information from parts of the brain to organs, causing a specific reaction or action in them while also collecting information about its condition and sending it to the brain, where it can be processed and acted upon. Therefore. However, in the autonomic nervous system the presence of efferents predominatesThat is to say that its main function is to emit signals in the direction of the organs.

    Neurons in the autonomic nervous system that connect to different organs in the body usually do so through the ganglia, having pre and postganglionic neurons. The action of the preganglionic neuron is always due to the action of acetylcholine, but in the neuron that interacts between the ganglion and the target organ the hormone released will vary depending on the subsystem (acetylcholine in the parasympathetic nervous system and norepinephrine in the sympathetic nervous system).

    main function

    The autonomic nervous system is one of the most vital systems for keeping us alive, mainly because of the function it performs.

    The main function of this system is the control, as we have indicated above, of unconscious and involuntary processes, such as breathing, blood circulation or digestion. It is responsible for keeping fit and activating the processes of internal organs and viscera, While allowing the detection and control of internal problems.

    It also prepares us to face specific situations involved in the environment, such as the secretion of saliva or digestive enzymes in the face of food vision, activation in the face of possible threats or the deactivation and regeneration of the system by rest.

    Any organism with the complexity of vertebrate animals needs a complete nervous system, with central nervous system and peripheral nervous system, to coordinate the different parts of the organism. And among invertebrates we also find simple nervous systems and other complexes, such as pop. Indeed, in animals it is necessary to quickly adapt to changes in the environment, to move, unlike fungi and plants.

    What controls the autonomic nervous system?

    As part of the nervous system responsible for controlling the proper functioning of the unconscious visceral, the autonomic or vegetative nervous system innervates most of the organs and bodily systems, with the exception of the muscles and joints which regulate voluntary movements.

    More precisely, we can see that this system controls the smooth muscles of the viscera and various organs such as the heart or lungs. It is also involved in the synthesis and expulsion of most secretions outside the body and part of the endocrine system, as well as metabolic processes and reflexes.

    Some of the organs and systems in which this system participates are as follows.

    1. Vision

    The autonomic nervous system governs pupil opening and ability to focus the gaze, Connection with the muscles of the iris and the whole of the eye.

    2. Heart and blood vessels

    Heart rate and blood pressure they are fundamental elements for human beings, which are governed unconsciously. In this way, it is the vegetative nervous system that is responsible for regulating these vital elements that keep us alive second by second.

    3. Lungs

    Although we are able to control breathing to some extent continuously breathing is not consciousJust as the general rule is not the pace at which we should inspire. Thus, breathing is also partially controlled by the autonomic nervous system.

    4. Digestive system

    Through food, humans are able to acquire the various nutrients that the body needs to continue to function. While eating behavior is consciously controlled, the process by which the digestive tract processes food and acquires its necessary components not, being the set of actions that the body performs during digestion involuntary and governed by the autonomic nervous system.

    5. Genitals

    Although the sexual act itself is performed consciously, all of the elements and physiological reactions that allow it to be performed are controlled primarily by the autonomic system, which governs processes such as erection and ejaculation. In addition, these processes are complicated when a feeling of fear or anxiety is felt, which links it to various physiological states.

    6. Secretion of enzymes and wastes

    Tears, sweat, urine, and feces are some of the substances the body expels from the environment. Its secretion and expulsion must be effected and / or may be impaired in part due to the functioning of the autonomic nervous system.. The same goes for the secretion of digestive enzymes and saliva.

    Parts of the autonomic nervous system

    In the autonomic nervous system we can find a series of subdivisions of great importance, which fulfill different functions. More precisely the sympathetic and parasympathetic nervous systems stand out, Which perform opposite functions in order to allow the existence of a balance in the activity of the organism.

    A third system can also be found, the enteric system, Which is primarily responsible for controlling the digestive tract.


    1. Sympathetic nervous system

    Being one of the divisions of the autonomic nervous system, the sympathetic system is responsible for preparing the body for action, Facilitate the fight or flight response to threatening stimuli. It does this by causing some body systems to speed up and inhibit the functioning of others, spending a lot of energy in the process.

    The mission of this part of the autonomic nervous system is to prepare the body to react quickly to risky situations, reducing the priority to certain biological processes and giving them to those that allow us to react quickly. This is why its function is ancestral traits, although no less useful; it adapts to modern life situations and can be triggered by relatively abstract ideas, such as the certainty that we will be late for a business meeting.

    2. Parasympathetic nervous system

    This branch of the autonomic nervous system is what is responsible for the return to a state of rest after a period of high energy expenditure. It is responsible for regulating and decelerating the body, allowing energy to be recovered while allowing the functioning of various systems. In other words, it is responsible for the regeneration of the body, but is also involved in the generation of orgasm, which does not seem to have much to do with other functions with which it shares biological roots. .

    3. Enteric nervous system

    While the parasympathetic nervous system also has a clear influence on the digestive tractThere is a subdivision of the autonomic nervous system that specializes almost exclusively in the system by which we incorporate nutrients into our bodies. It is the enteric system, which innervates the digestive tract and regulates its normal functioning.

    As it is responsible for one of the most important systems for survival, the enteric nervous system must be fundamentally automatic, and constantly worry about maintaining the biochemical balance that exists in the different environments of the body, adapting the alterations that may arise depending on ingested, state of activation, hormones circulating in the blood, etc.

    Bibliographical references:

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    • Guyton, AC and Hall, J. (2006). Treatise on medical physiology. Elsevier; 11th edition.
    • Purves, D., Augustine, GJ, Fitzpatrick, D., Hall, WC, LaMantia, AS, McNamara, JO, White, LE (2008). Neurosciences. Sinauer Associates.
    • Schatzberg, A., Nemeroff, CS (2006). Treatise on psychopharmacology. Elsevier.
    • Snell, RD (1997). Autonomous nervous system. In: Clinical Neuroanatomy, (pp. 449-478). Buenos Aires: Pan American.
    • Tortora, GJ, Derrickson, B. (2016). Principles of Anatomy and Physiology (15th edition). Hoboken: Wiley.

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