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Autonomic nervous system: structures and functions

Autonomic nervous system: structures and functions

May 1, 2024

Throughout our lives we perform a lot of actions. We run, we jump, we talk ... All these acts are voluntary elements that we do voluntarily. However, also we do a lot of things that we are not even aware of, many of which are in fact those that keep us alive and with the possibility of doing the voluntary ones, such as the control of the heart and respiratory rhythm, the acceleration or deceleration of the physiological systems or the digestion.

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


What is the vegetative nervous system?

The autonomic nervous system, also called vegetative nervous system , is one of the two divisions that have been made of the nervous system at the functional level. This system takes care of connect the neurons of the central nervous system with those of the rest of the body systems and organs , forming part of both the central nervous system and peripheral. Its basic function is the control of the internal processes of the organism, that is to say of the viscera, being the processes ruled by this system alien to our will.

The connections with the different target organs of this system are both motor and sensitive, having both eferences and afferences. It is therefore a system that sends information from the parts of the brain to the organs, provoking in them a specific reaction or action while at the same time recapturing information about their status and sending it to the brain, where it can be processed and act accordingly. . Despite this, in the autonomic nervous system the presence of eferences predominates , that is to say, that its function is mostly to emit signals in the direction of the organs.


The neurons of the autonomic nervous system that connect with the various organs of the body do so as a rule 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 according to the subsystem (acetylcholine in the parasympathetic nervous system and noradrenaline in the sympathetic nervous system) .

Principal function

The autonomic nervous system is one of the most vital systems to keep us alive, mainly due to the function it performs.

The main function of this system is the control, as we have previously indicated, of unconscious and involuntary processes, such as respiration, blood circulation or digestion. It is responsible for keeping fit and activated the processes of the internal organs and viscera , at the same time that allows the detection and control of internal problems .


It also prepares us to deal with specific situations mediated by the environment, such as the secretion of saliva or digestive enzymes in view of food, the activation of possible threats or the deactivation and regeneration of the system through rest.

What controls the autonomic nervous system?

As part of the nervous system responsible for controlling the proper unconscious visceral functioning, the autonomic or vegetative nervous system is innervating most organs and body systems, with the exception of the muscles and joints that govern voluntary movement.

Specifically, we can find that this system controls the smooth musculature of the viscera and various organs such as the heart or lungs . It also participates in the synthesis and expulsion of most secretions to the outside of the body and part of the endocrine, as well as in metabolic processes and reflexes.

Some of the organs and systems in which this system has participation are the following.

1. Vision

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

2. Heart and blood vessels

The heartbeat and blood pressure they are fundamental elements for the human being, 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

While we are able to control breathing to a certain extent the fact of breathing continuously is not conscious , as well as as a general rule, neither is the rhythm with which we need to inhale. Thus, breathing is also partially controlled by the autonomic nervous system.

4. Digestive tube

Through food the human being is able to acquire the various nutrients that the body needs to continue functioning. While the eating behavior is consciously controlled by the process by which the digestive tube transforms the food and acquires the 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, the set of elements and physiological reactions that allow its realization are controlled primarily by the autonomous system, which governs processes such as erection and ejaculation . In addition, these processes become complicated when you experience a sense of fear or anxiety, something that links you to various physiological states.

6. Secretion of enzymes and waste

Tears, sweat, urine and feces are some of the substances that the body expels to the environment. Its secretion and expulsion is due to and / or may be altered in part due to the functioning of the autonomic nervous system . The same happens with the secretion of digestive enzymes and saliva.

Parts of the autonomic nervous system

Within the autonomic nervous system we can find a series of very important subdivisions that perform differentiated functions . Specifically highlight the sympathetic nervous system and the parasympathetic , that perform opposite functions in order to allow the existence of a balance in the activity of the organism. You can also find a third system, the enteric system , which is mainly responsible for the control of 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 agency for action , facilitating the fight or flight response to threatening stimuli. For this it produces an acceleration of some systems of the organism and inhibits the functioning of others, making a great expenditure of energy in the process.

The mission of this part of the autonomic nervous system is to prepare the body to respond agilely to situations of risk, subtracting priority to certain biological processes and granting them to those that allow us to react with agility. That is why its function is of ancestral characteristics, although that is not the least useful; it adapts to the situations of modern life and can be activated 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 the one is responsible for returning to a state of rest after a period of high energy expenditure . It is responsible for regulating and decelerating the body, allowing energy recovery while allowing the operation of various systems. In other words, it is responsible for the regeneration of the organism, although it also intervenes in the generation of orgasm, something that does not seem to have much to do with the 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 tract , there is a subdivision of the autonomic nervous system that specializes almost exclusively in the system by which we incorporate nutrients into our body. 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 essentially automatic, and constantly worry about maintaining the biochemical balance that exists in the different media of the organism, adapting to the alterations that may occur depending on what is ingested, of the state of activation, of the hormones circulating in the blood, etc.

Bibliographic references

  • Kandel, E.R .; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.
  • Guyton, A. C. & Hall, J. (2006). Treaty of Medical Physiology. Elsevier; 11th edition.
  • Snell, R.D. (1997). Autonomic nervous system. In: Clinical neuroanatomy, (pp 449-478). Buenos Aires: Panamericana.

Autonomic Nervous System: Crash Course A&P #13 (May 2024).


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