Autonomic Nervous System- Anatomy, Function & Disorders

Autonomic Nervous System: Divisions, Functions, Anatomy, Function, Disorders

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:51 PM IST

The autonomic nervous system (ANS) is a vital part of the human nervous system that controls involuntary functions like heart rate, digestion, respiration, and glandular activities. It is divided into the sympathetic and parasympathetic divisions, which work together to maintain homeostasis. The ANS ensures smooth coordination of the body's internal organs, adapting to changing needs without conscious effort. In this article, the autonomic nervous system (ans), structure of the autonomic nervous system, autonomic nervous system functions, and disorders of the autonomic nervous system are discussed. Autonomic Nervous System is a topic of the chapter Neural Control and Coordination in Biology.

This Story also Contains

What is the Autonomic Nervous System (ANS)?
Structure of the Autonomic Nervous System
Autonomic Nervous System Functions
Disorders of the Autonomic Nervous System

Autonomic Nervous System: Divisions, Functions, Anatomy, Function, Disorders

What is the Autonomic Nervous System (ANS)?

The autonomic nervous system is one of the crucial subdivisions of the PNS. It governs such involuntary activities as heartbeat, blood pressure, digestion rate, and respiratory rate. It runs beneath conscious awareness to maintain homeostasis and to respond to stress.

Two main branches that constitute the ANS are the sympathetic nervous system, which prepares the body for situations concerning 'fight or flight', and the parasympathetic nervous system, leading to 'rest and digest'. These two systems ensure that the body adjusts to various demands but stays balanced within itself.

The autonomic nervous system plays an essential role in homeostasis because it controls most of the fundamental, vital activities in the body subconsciously. It provides prompt responses to stressors and thus maintains survival and optimal organ functions by distributing energy to sustain life processes like circulation, respiration, and digestion.

Structure of the Autonomic Nervous System

The ANS is complex in terms of the anatomical basis of its multiple components and pathways through which it exercises its control over bodily functions. There are two main divisions, along with various neurons and ganglia, that function together to transmit signals.

Division of the ANS

Sympathetic nervous system: This prepares the body for intense physical activity and stress.
Parasympathetic Nervous System: Anabolic predominance for rest and recovery.

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The Components of the ANS

Preganglionic Neurons: Those originating in the central nervous system that convey the signal to the autonomic ganglia.
Postganglionic Neurons: Receives signals from preganglionic neurons and innervates target organs.

Anatomy of Autonomic Ganglia

Found in various parts of the body; serve as relay stations for nerve impulses.
Enable nerve impulses from the CNS to reach the target organs.

Autonomic Nervous System

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Autonomic Nervous System Functions

The ANS is responsible for maintaining homeostasis and bringing about an appropriate response to stimuli.

Sympathetic division

Through vasoconstriction, it redirects blood flow away from the gastrointestinal system and skin.
Peristalsis is inhibited by it.
It improves blood flow to the skeletal muscles and lungs.
By using epinephrine to dilate the bronchioles, it permits increased oxygen exchange in the alveoli.
It increases heart rate and contracts cardiac cells to improve blood flow in the skeletal muscles.
It improves eye vision by relaxing the ciliary muscles and dilation of the pupils.
It dilates the heart's coronary arteries.
The intestinal and urinary sphincters are constricted.
It facilitates orgasm stimulation.

Parasympathetic division

By widening the blood arteries, it enhances the flow of blood to the gastrointestinal system.
When oxygen is not required, it constricts the bronchioles.
The heart is parasympathetically controlled by the vagus nerves in the cardiac branches
It allows for closer vision by constricting the pupil and contracting the ciliary muscles.
By activating the salivary glands, it speeds up peristalsis and improves nutrient absorption.
They participate in the erection of genital tissues and increase sexual desire.

Enteric Nervous System

It detects alterations in the gut's chemistry and mechanics.
It controls the gut's secretions.
It alters the movements of the peristaltic

Disorders of the Autonomic Nervous System

Several disorders and diseases are associated with the ANS; they cause severe health complications.

Dysautonomia

Genetic inheritance, autoimmune diseases, or injury; major symptoms: fainting, unstable blood pressure, and digestive problems
Diagnosed by autonomic function tests; medicines and changes in lifestyle for treatment.

Other Disorders of the ANS

Postural Orthostatic Tachycardia Syndrome (POTS): Rapid heartbeat upon standing.
Autonomic Neuropathy: It is the damage to autonomic nerves and it is usually seen in the case of Diabetes.

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Frequently Asked Questions (FAQs)

1. What is the autonomic nervous system and what is its function?

The autonomic nervous system controls involuntary functions, such as the rate of heartbeats, digestion rate, respiratory rate, etc. It maintains homeostasis.

2. How is the sympathetic nervous system different from the parasympathetic nervous system?

The sympathetic system prepares the body for 'fight or flight' responses and the parasympathetic system prepares it for 'rest and digest' activities.

3. What are the common disorders of the autonomic nervous system?

Common disorders include Dysautonomia, Postural Orthostatic Tachycardia Syndrome, and Autonomic Neuropathy.

4. How is autonomic nervous system dysfunction diagnosed?

These range from autonomic function testing and heart rate variability tests to tilt table testing in some cases.

5. What are the available treatments for the disorders of the autonomic nervous system?

Treatments include medications, changes in lifestyle and physical therapy, and, in some cases, alternative therapies like biofeedback.

6. How do neurotransmitters function in the autonomic nervous system?

Neurotransmitters are chemical messengers that transmit signals between neurons in the autonomic nervous system. The main neurotransmitters in the ANS are acetylcholine and norepinephrine. Acetylcholine is used by all preganglionic neurons and parasympathetic postganglionic neurons, while norepinephrine is used by most sympathetic postganglionic neurons.

7. How does chronic stress affect the autonomic nervous system?

Chronic stress can lead to prolonged activation of the sympathetic nervous system, which can disrupt the balance of the ANS. This can result in various health problems, including cardiovascular issues, digestive disorders, and mental health conditions.

8. How does the autonomic nervous system influence sexual function?

The ANS plays a crucial role in sexual arousal and function. The parasympathetic division is primarily responsible for sexual arousal, causing increased blood flow to the genitals. The sympathetic division is involved in orgasm and ejaculation in males.

9. How does the autonomic nervous system affect the immune system?

The ANS interacts closely with the immune system. The sympathetic division generally suppresses immune responses, while the parasympathetic division, particularly through the vagus nerve, can enhance certain immune functions. This interaction is part of the field known as psychoneuroimmunology.

10. How does the autonomic nervous system regulate blood glucose levels?

The ANS plays a role in glucose regulation by influencing the release of insulin and glucagon from the pancreas. The sympathetic division stimulates glucagon release (increasing blood glucose), while the parasympathetic division stimulates insulin release (decreasing blood glucose).

11. What is the role of the parasympathetic nervous system?

The parasympathetic nervous system is often referred to as the "rest and digest" system. It promotes relaxation, conserves energy, and regulates bodily functions during normal conditions. It slows heart rate, stimulates digestion, and promotes other restorative processes.

12. How does the autonomic nervous system affect the respiratory system?

The ANS regulates breathing rate and depth. The sympathetic division increases respiratory rate and dilates bronchioles, while the parasympathetic division generally has the opposite effect. This control allows for rapid adjustments in oxygen intake based on the body's needs.

13. What is the role of the autonomic nervous system in thermoregulation?

The ANS plays a crucial role in thermoregulation by controlling sweat glands, blood vessel dilation/constriction, and shivering. The sympathetic division activates sweat glands and causes blood vessel constriction in cold conditions, while the parasympathetic division promotes heat dissipation through vasodilation.

14. How does the autonomic nervous system affect the urinary system?

The ANS controls bladder function and urination. The sympathetic division promotes urine storage by relaxing the bladder and contracting the internal urethral sphincter. The parasympathetic division facilitates urination by contracting the bladder and relaxing the sphincter.

15. How does the autonomic nervous system control pupil dilation?

Pupil dilation is controlled by the opposing actions of the sympathetic and parasympathetic divisions. The sympathetic system causes pupil dilation (mydriasis) in low light or during stress, while the parasympathetic system causes pupil constriction (miosis) in bright light or during close focus.

16. How does the autonomic nervous system affect the skin?

The ANS regulates several skin functions. The sympathetic division controls sweat glands and causes piloerection (goosebumps), while both divisions influence blood flow to the skin, affecting temperature regulation and blushing.

17. What is the relationship between the autonomic nervous system and blood pressure regulation?

The ANS plays a crucial role in short-term blood pressure regulation. The sympathetic division can increase blood pressure by constricting blood vessels and increasing heart rate and contractility. The parasympathetic division can decrease blood pressure by slowing heart rate.

18. How does the autonomic nervous system affect the eyes beyond pupil dilation?

In addition to controlling pupil size, the ANS influences tear production (parasympathetic), focusing of the lens (parasympathetic), and blood flow to the eye (sympathetic). It also plays a role in the regulation of intraocular pressure.

19. How does the autonomic nervous system affect the liver?

The ANS influences liver function through both sympathetic and parasympathetic innervation. It regulates blood flow to the liver, glucose metabolism, and bile production. The sympathetic system generally promotes glucose release from the liver, while the parasympathetic system promotes glucose storage.

20. What is autonomic dysreflexia and who is at risk?

Autonomic dysreflexia is a potentially dangerous complication that can occur in individuals with spinal cord injuries above the T6 level. It involves an overreaction of the sympathetic nervous system to stimuli below the level of injury, leading to sudden, severe increases in blood pressure.

21. What is autonomic balance and why is it important?

Autonomic balance refers to the equilibrium between sympathetic and parasympathetic activity. It's crucial for maintaining homeostasis and overall health. Imbalances can lead to various disorders, including cardiovascular problems, digestive issues, and mood disorders.

22. What is autonomic dysfunction and what are some common symptoms?

Autonomic dysfunction, also known as dysautonomia, occurs when the autonomic nervous system doesn't work properly. Common symptoms include dizziness, fainting, rapid or slow heart rate, blood pressure problems, digestive issues, and abnormal sweating.

23. What is autonomic neuropathy and what causes it?

Autonomic neuropathy is damage to the nerves that carry information from the brain and spinal cord to the heart, blood vessels, bladder, intestines, and other organs. It can be caused by various factors including diabetes, certain autoimmune diseases, and some medications.

24. What is autonomic hyperreflexia and why is it dangerous?

Autonomic hyperreflexia is a potentially life-threatening condition that can occur in individuals with spinal cord injuries. It involves an overreaction of the sympathetic nervous system to stimuli below the level of injury, leading to dangerous spikes in blood pressure, severe headaches, and other symptoms.

25. What is the role of the vagus nerve in the autonomic nervous system?

The vagus nerve is a major component of the parasympathetic nervous system. It innervates many organs in the chest and abdomen, regulating heart rate, digestion, and other functions. It's also involved in the inflammatory reflex, linking the nervous system and immune system.

26. How does the "fight or flight" response relate to the autonomic nervous system?

The "fight or flight" response is primarily controlled by the sympathetic division of the autonomic nervous system. When activated, it prepares the body for immediate action by increasing heart rate, dilating pupils, and redirecting blood flow to muscles, among other effects.

27. What is the significance of the hypothalamus in autonomic function?

The hypothalamus is a crucial control center for the autonomic nervous system. It integrates information from various parts of the brain and body, and coordinates appropriate autonomic responses. It plays a key role in maintaining homeostasis by regulating functions such as body temperature, hunger, thirst, and circadian rhythms.

28. How does the autonomic nervous system affect the cardiovascular system?

The ANS regulates heart rate and blood pressure. The sympathetic division increases heart rate and blood pressure, while the parasympathetic division decreases them. This dual control allows for rapid adjustments in response to changing physiological needs.

29. How does the autonomic nervous system influence digestion?

The ANS plays a significant role in digestion. The parasympathetic division stimulates digestive processes by increasing peristalsis, enzyme secretion, and blood flow to the digestive organs. The sympathetic division, when activated, generally inhibits these processes to conserve energy for other functions.

30. What is the enteric nervous system and how does it relate to the ANS?

The enteric nervous system is often called the "second brain" and is a network of neurons in the walls of the digestive tract. While it can function independently, it's considered part of the autonomic nervous system and interacts closely with both the sympathetic and parasympathetic divisions to regulate digestive functions.

31. What are the two main divisions of the autonomic nervous system?

The two main divisions of the autonomic nervous system are the sympathetic nervous system and the parasympathetic nervous system. These two systems generally work in opposition to maintain homeostasis in the body.

32. How does the autonomic nervous system influence metabolism?

The ANS plays a crucial role in metabolism. The sympathetic division generally increases metabolic rate, promoting the breakdown of glycogen and fat. The parasympathetic division promotes energy conservation and the storage of nutrients.

33. What is the role of the autonomic nervous system in exercise?

During exercise, the ANS helps to meet increased physiological demands. The sympathetic division increases heart rate, blood pressure, and respiratory rate, and redirects blood flow to muscles. After exercise, the parasympathetic division helps return these parameters to baseline.

34. How does the autonomic nervous system influence inflammation?

The ANS plays a significant role in regulating inflammation. The parasympathetic nervous system, particularly through the vagus nerve, can suppress inflammation in a pathway known as the inflammatory reflex. The sympathetic nervous system can both promote and inhibit inflammation depending on the context.

35. What is autonomic tone and how is it maintained?

Autonomic tone refers to the baseline level of activity in the sympathetic and parasympathetic nervous systems. It's maintained through constant, subtle adjustments by the ANS to keep the body in a state of balance. Proper autonomic tone is crucial for maintaining homeostasis.

36. What is the autonomic nervous system and how does it differ from the somatic nervous system?

The autonomic nervous system (ANS) is a division of the peripheral nervous system that controls involuntary bodily functions, such as heart rate, digestion, and breathing. It differs from the somatic nervous system, which controls voluntary movements, in that the ANS operates largely unconsciously and regulates internal organ functions.

37. What is the baroreceptor reflex and how does it relate to the ANS?

The baroreceptor reflex is a homeostatic mechanism for maintaining blood pressure. Baroreceptors in blood vessels detect changes in blood pressure and send signals to the brain, which then adjusts heart rate and blood vessel constriction via the autonomic nervous system to maintain stable blood pressure.

38. What is autonomic testing and when is it used?

Autonomic testing involves a series of non-invasive tests to evaluate the function of the autonomic nervous system. It's used when autonomic dysfunction is suspected, and may include tests of heart rate variability, blood pressure response to position changes, and sweat function.

39. How does the autonomic nervous system change with aging?

As we age, there's often a gradual decline in autonomic function. This can lead to reduced heart rate variability, slower responses to postural changes, and decreased sweating. These changes can increase the risk of falls, heat intolerance, and other health issues in older adults.

40. What is the relationship between the autonomic nervous system and circadian rhythms?

The ANS plays a crucial role in maintaining circadian rhythms, our internal 24-hour clock. It regulates daily fluctuations in body temperature, hormone release, and sleep-wake cycles. Disruptions to the ANS can lead to sleep disorders and other circadian rhythm disturbances.

41. What is the role of the autonomic nervous system in pain perception?

The ANS is involved in pain modulation. Sympathetic activation can enhance pain perception in some cases, while parasympathetic activation can have pain-relieving effects. The ANS also influences the body's stress response to pain.

42. What is the relationship between the autonomic nervous system and the endocrine system?

The ANS and endocrine system work closely together to maintain homeostasis. The ANS can directly stimulate or inhibit hormone release from various glands, while hormones can influence autonomic function. This interaction is part of the neuroendocrine system.

43. What is autonomic failure and how does it differ from autonomic dysfunction?

Autonomic failure refers to a severe, often progressive loss of autonomic function, while autonomic dysfunction is a broader term that can include milder or more localized problems. Autonomic failure can result in severe issues with blood pressure regulation, thermoregulation, and other vital functions.

44. How does the autonomic nervous system contribute to emotional responses?

The ANS plays a key role in the physiological aspects of emotions. For example, the sympathetic "fight or flight" response contributes to feelings of fear or anger, while parasympathetic activation can contribute to feelings of calm and contentment.

45. How does the autonomic nervous system affect sleep?

The ANS plays a crucial role in the sleep-wake cycle. Parasympathetic activity generally increases during sleep, promoting rest and recovery. The ANS also regulates changes in body temperature, heart rate, and other physiological parameters that occur during different sleep stages.

46. What is autonomic storming and when does it occur?

Autonomic storming, also known as paroxysmal sympathetic hyperactivity, is a condition characterized by episodes of extreme sympathetic nervous system activation. It can occur after severe brain injuries and is marked by rapid heart rate, high blood pressure, sweating, and other symptoms.

47. How does the autonomic nervous system influence gastrointestinal motility?

The ANS regulates gastrointestinal motility through its effects on smooth muscle in the digestive tract. The parasympathetic division generally increases motility and secretions, while the sympathetic division tends to decrease them.

48. How does the autonomic nervous system affect the pancreas?

The ANS influences pancreatic function by regulating the release of digestive enzymes and hormones. The parasympathetic division stimulates the release of digestive enzymes and insulin, while the sympathetic division can stimulate glucagon release.

49. What is autonomic dysregulation in autism spectrum disorders?

Autonomic dysregulation in autism spectrum disorders refers to abnormalities in ANS function that are often observed in individuals with autism. This can manifest as differences in heart rate variability, skin conductance responses, and other autonomic functions.

50. How does the autonomic nervous system contribute to the stress response?

The ANS, particularly the sympathetic division, is a key component of the stress response. It works in conjunction with the hypothalamic-pituitary-adrenal (HPA) axis to produce the physiological changes associated with stress, such as increased heart rate and blood pressure.

51. What is the role of the autonomic nervous system in thermoregulation during fever?

During a fever, the ANS helps to raise and maintain body temperature. The sympathetic division causes vasoconstriction to reduce heat loss and increases metabolic rate. Once the fever breaks, the ANS promotes heat loss through vasodilation and sweating.

52. How does the autonomic nervous system affect saliva production?

Saliva production is primarily controlled by the parasympathetic nervous system. Parasympathetic stimulation increases both the volume and enzyme content of saliva. Sympathetic stimulation can also affect saliva, typically producing a small amount of protein-rich saliva.

53. What is the relationship between the autonomic nervous system and chronic pain conditions?

Chronic pain conditions often involve dysregulation of the ANS. This can manifest as increased sympathetic activity, decreased parasympathetic activity, or both. These autonomic changes can contribute to pain persistence and associated symptoms like fatigue and sleep disturbances.

54. How does the autonomic nervous system influence bone metabolism?

The ANS plays a role in bone metabolism, although this is an area of ongoing research. Sympathetic nervous system activation generally promotes bone resorption, while parasympathetic activity may have a protective effect on bone mass.

55. What is the role of the autonomic nervous system in addiction and substance use disorders?

The ANS is involved in many aspects of addiction, including the physiological responses to drug use and withdrawal. Chronic substance use can lead to changes in autonomic function, which may contribute to cravings and difficulty in maintaining abstinence. Understanding these autonomic changes is important for developing effective treatments for addiction.