Autonomic Nervous System

Overview

What is the autonomic nervous system?

Your autonomic nervous system is a part of your overall nervous system that controls the automatic functions of your body that you need to survive. These are processes you don’t think about and that your brain manages while you’re awake or asleep.

Where does the autonomic nervous system fit in the overall structure of the nervous system?

Your overall nervous system includes two main subsystems:

  • Central nervous system: This includes your brain (your retina and optic nerve in your eyes are considered part of your brain, structure-wise) and spinal cord.
  • Peripheral nervous system: This includes every part of your nervous system that isn’t your brain and spinal cord.

Your peripheral nervous system also has two subsystems:

  • Somatic nervous system: This includes muscles you can control, plus all the nerves throughout your body that carry information from your senses. That sensory information includes sound, smell, taste and touch. Vision doesn’t fall under this because the parts of your eyes that manage your sight are part of your brain.
  • Autonomic nervous system: This is the part of your nervous system that connects your brain to most of your internal organs.

Function

What does the autonomic nervous system do?

Your autonomic nervous system breaks down into three divisions, each with its own job:

  • Sympathetic nervous system: This system activates body processes that help you in times of need, especially times of stress or danger. This system is responsible for your body’s “fight-or-flight” response.
  • Parasympathetic nervous system: This part of your autonomic nervous system does the opposite of your sympathetic nervous system. This system is responsible for the “rest-and-digest” body processes.
  • Enteric nervous system: This part of your autonomic nervous system manages how your body digests food.

How does the autonomic nervous system help with other organs?

Much like a home needs electrical wiring to control lights and everything inside that needs power, your brain needs the autonomic nervous system’s network of nerves. These nerves are the physical connections your brain needs to control almost all of your major internal organs.

Organ functions controlled through your autonomic nervous system

Your autonomic nervous system has the following effects on your body’s systems:

  • Eyes: Your autonomic nervous system doesn’t involve your vision directly. However, it does manage the width of your pupils (controlling how much light enters your eyes) and the muscles your eyes use to focus.
  • Lacrimal (eyes), nasopharyngeal (nose) and salivary (mouth) glands: Your autonomic nervous system controls your tear system around your eyes, how your nose runs and when your mouth waters.
  • Skin: Your autonomic nervous system controls your body’s ability to sweat. It also controls the muscles that cause hair to stand up. This reaction is commonly called “goosebumps” or “gooseflesh.”
  • Heart and circulatory system: The autonomic nervous system controls how fast and hard your heart pumps and the width of blood vessels. Those abilities are how your autonomic system helps manage your heart rate and blood pressure.
  • Immune system: Your parasympathetic nervous system can trigger reactions from your immune system. That can happen with infections, asthma attacks and allergic reactions, to name a few.
  • Lungs: Your autonomic nervous system manages the width of your airway and the network of passages that carry air into and out of your lungs.
  • Intestines and colon: Your autonomic nervous system manages the digestion process from your small intestine to your colon. Your autonomic nervous system also holds the muscles closed at your rectum until you’re ready to relieve yourself and defecate (poop).
  • Liver and pancreas: Your autonomic nervous system controls when your pancreas releases insulin and other hormones, and when your liver converts different molecules that hold stored energy into glucose that your cells can use.
  • Urinary tract: Your autonomic nervous system manages your bladder muscles, including the muscles that hold it closed until you're ready to relieve yourself and urinate (pee).
  • Reproductive system: Your autonomic system plays a key role in your body’s sexual functions, including feeling aroused (erections and secreting fluids that provide lubrication during sex) and the ability to orgasm.

What are some interesting facts about the autonomic nervous system?

  • Your sympathetic and parasympathetic systems create a balancing act. Your sympathetic nervous system activates body processes, and your parasympathetic deactivates or lowers them. That balance is key to your body's well-being and your ongoing survival.
  • It involves multiple forms of communication. Your nervous system uses chemical compounds produced by various glands in your body and brain as signals for communication. It also uses electrical energy in the neurons themselves. The neurons switch back and forth between electrical and chemical communication as needed.
  • Your enteric nervous system is very complex. Some experts describe it as part of the overall nervous system instead of the autonomic nervous system. That’s because there are as many neurons (specialized cells that make up your brain, spinal cord and nerves) in your enteric nervous system as there are in your spinal cord.

Anatomy

Where is it located?

Your autonomic nervous system includes a network of nerves that extend throughout your head and body. Some of those nerves extend directly out from your brain, while others extend out from your spinal cord, which relays signals from your brain into those nerves.

There are 12 cranial nerves, which use Roman numerals to set them apart, and your autonomic nervous system has nerve fibers in four of them. These include the third, seventh, ninth and 10th cranial nerves. They manage pupil dilation, eye focusing, tears, nasal mucus, saliva and organs in your chest and belly.

Your autonomic nervous system also uses most of the 31 spinal nerves. These include spinal nerves in your thoracic (chest and upper back), lumbar (lower back) and sacral (tailbone).

The spinal nerve connections are how your autonomic system controls the following:

  • Heart.
  • Lungs.
  • Liver.
  • Pancreas.
  • Spleen.
  • Stomach.
  • Small and large intestine.
  • Colon.
  • Kidney.
  • Bladder.
  • Sexual organs.

The part of your brain that runs autonomic functions is your hypothalamus. This structure isn’t part of your autonomic nervous system, but is a key part of how it works.

What is it made of?

Your autonomic nervous system has a similar makeup to your overall nervous system. The main cell types are as follows, with more about them listed below:

  • Neurons: These cells send and relay signals, and makeup parts of your brain, spinal cord and nerves. They also convert signals between the chemical and electrical forms.
  • Glial cells: These cells don’t transmit or relay nervous system signals. Instead, they’re helpers or support cells for the neurons.
  • Nuclei: These are nerve cell clusters grouped together because they have the same jobs or connections.
  • Ganglia: These, pronounced “gang-lee-uh,” are groups of related nerve cells (one of these is a ganglion, pronounced “gang-lee-on”). They usually don’t all have the same jobs or connections, but they’re in roughly the same area or have connections to the same systems. Examples of this are the cochlear and vestibular ganglia, which are part of your senses of hearing and balance.

Neurons

Each neuron consists of the following:

  • Cell body: This is the main part of the cell.
  • Axon: This is a long, arm-like extension. At the end of an axon are several finger-like extensions where the electrical signal in the neuron becomes a chemical signal. These extensions, or synapses, connect with nearby nerve cells.
  • Dendrites: These are small branch-like extensions (their name comes from a Latin word that means “tree-like”) on the cell body. Dendrites receive the chemical signals sent from synapses of other nearby neurons.
  • Myelin: This is a thin layer composed of fatty compounds. Myelin is a protective covering that surrounds the axon of many neurons.

The dendrites on a single neuron may connect to thousands of other synapses. Some neurons are longer or shorter, depending on their location in your body and what they do.

Glial cells

Glial (pronounced “glee-uhl”) cells do several different jobs. They help develop and maintain neurons when you’re young and manage how neurons work throughout your life. They shield your nervous system from infections, control the chemical balance in your nervous system and coat neurons’ axons with myelin. There are 10 times more glial cells than neurons.

Conditions and Disorders

What are the common conditions and disorders that affect the autonomic nervous system?

There are many conditions and causes of autonomic neuropathy, which means damage or disease that affects your autonomic nervous system. Common examples include:

  • Type 2 diabetes. Uncontrolled Type 2 diabetes can damage your autonomic nervous system over time. An example of this is orthostatic hypotension, where your blood pressure drops when you stand up. Diabetic neuropathy can damage the nerves that normally trigger a blood pressure increase reflex when you stand.
  • Amyloidosis. This condition causes long-term nerve damage because malfunctioning protein molecules build up in various parts of your body.
  • Autoimmune and inflammatory conditions. A major example of this is Guillain-Barré syndrome.
  • Congenital and genetic conditions. These are disorders or conditions you have at birth. You have genetic conditions because you inherit them from one or both parents. An example of this is Hirschsprung’s disease.
  • Infections. Nerve damage can happen because of viruses such as HIV or bacteria from insect bites that cause Lyme disease or Chagas disease. Other infections that can also do this include botulism or tetanus.
  • Multiple system atrophy. This severe condition is similar to Parkinson’s disease, damaging autonomic nerves over time.
  • Poisons and toxins. Toxic heavy metals like mercury or lead can damage autonomic nerves. Many industrial chemicals can also cause this kind of damage. Alcohol can also have toxic effects on your autonomic nerves.
  • Trauma. Injuries can cause nerve damage, which may be long-term or even permanent. This is especially the case when you have injuries to your spinal cord that damage or cut off autonomic connections farther down.
  • Tumors. Cancer and benign (harmless) growths can both disrupt your autonomic nervous system.

Common signs or symptoms of body organ conditions?

The symptoms of autonomic nervous system conditions depend on the location of the damage. With conditions like Type 2 diabetes, the damage can happen in many places throughout your body. The most likely symptoms of autonomic nervous system damage include:

Common tests to check the health of the body organ?

Several tests can help in diagnosing autonomic nervous system problems. These include:

Common treatments for the body organ?

The treatments for autonomic nervous system conditions can be very specific, depending on the condition in question. Some of them might treat the condition itself or an underlying cause. Others might only treat symptoms of the condition, especially when there’s no cure or treatment for the condition. That means there isn’t a one-treatment-fits-all approach to these conditions. Medications can help with some of these conditions, but not all of them.

Care

How can I prevent autonomic nervous system conditions and problems?

Prevention of autonomic nervous system damage is the best way to avoid conditions that affect that system. The best preventive actions you can take include:

  • Eat a balanced diet. Vitamin deficiencies, especially vitamin B12, can damage your autonomic nervous system.
  • Avoid abusing drugs and alcohol. Abusing prescription and recreational drugs, as well as alcohol, can damage your autonomic nervous system.
  • Stay physically active and maintain a healthy weight. This can also help prevent or delay the onset of Type 2 diabetes, which damages your autonomic nerves over time. It can also help you avoid injuries that might damage areas of your spinal cord that could have autonomic nervous system impacts.
  • Wear safety equipment as needed. Injuries are a major source of nerve damage. Using safety equipment during work and play activities can protect you from these types of injuries, or limit the severity of the injuries.
  • Manage chronic conditions as recommended. If you have a chronic condition that can affect your autonomic nerves — especially Type 2 diabetes — you should take steps to manage this condition. That can limit the effects of the condition or delay how long it takes to get worse. Your healthcare provider can help guide you on ways to manage this condition.

A note from Cleveland Clinic

Your autonomic nervous system is a vital part of how you live your life. You don’t even have to think about it most of the time and it will keep doing its job. Taking care of your body, especially your nervous system, is the best way to avoid conditions that can cause autonomic nerve damage. That way, you can keep focusing on what you want to pay attention to in your life.

Last reviewed by a Cleveland Clinic medical professional on 06/15/2022.

References

  • Amthor FR. Chapter 18: Autonomic Nervous System: Sympathetic, Parasympathetic, & Enteric. (https://neurology-mhmedical-com.ccmain.ohionet.org/content.aspx?sectionid=247989153&bookid=2938&Resultclick=2#1174243513) In: Amthor FR, Theibert AB, Standaert DG, Roberson ED. eds. Essentials of Modern Neuroscience. McGraw Hill; 2020. Accessed 6/15/2022.
  • Calabrò RS, Cacciola A, Bruschetta D, et al. Neuroanatomy and function of human sexual behavior: A neglected or unknown issue? (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6908863/) Brain Behav. 2019;9(12):e01389. Accessed 6/15/2022.
  • Chapter 9: Autonomic Nervous System. (https://neurology-mhmedical-com.ccmain.ohionet.org/content.aspx?sectionid=248914692&bookid=2963#1174973907) In: Nestler EJ, Kenny PJ, Russo SJ, Schaefer A. eds. Nestler, Hyman & Malenka’s Molecular Neuropharmacology: A Foundation for Clinical Neuroscience, 4e. McGraw Hill; 2020. Accessed 6/15/2022.
  • Chapter 25: Disorders of the Autonomic Nervous System, Respiration, and Swallowing. (https://neurology-mhmedical-com.ccmain.ohionet.org/content.aspx?sectionid=146911420&bookid=1477&Resultclick=2#1162593019) In: Ropper AH, Samuels MA, Klein JP, Prasad S. eds. Adams and Victor's Principles of Neurology, 11e. McGraw Hill; 2019. Accessed 6/15/2022.
  • Kaiser JT, Lugo-Pico JG. Neuroanatomy, Spinal Nerves. (https://www.ncbi.nlm.nih.gov/books/NBK542218/) [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Accessed 6/15/2022.
  • Waxenbaum JA, Reddy V, Varacallo M. Anatomy, Autonomic Nervous System. (https://www.ncbi.nlm.nih.gov/books/NBK539845/) [Updated 2021 Jul 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Accessed 6/15/2022.
  • Waxman SG. eds. Clinical Neuroanatomy, 29e. McGraw Hill; 2020. Chapters 1, 2, 5, 8 and 20 reviewed on 1/11/2021. Accessed 6/15/2022.

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