Definition and Overview
The autonomic nervous system (ANS) is a nervous system that automatically regulates the functions of internal organs. Almost all organs, including the heart, lungs, gastrointestinal tract, bladder, and blood vessels, are under the control of the autonomic nervous system and play a role in maintaining the balance of the body's internal environment without conscious effort.
The name autonomic nervous system was first used by British physiologist Langley in 1898. Langley divided the autonomic nervous system into three branches, the sympathetic nervous system, parasympathetic nervous system, and enteric nervous system, according to the location of the nerves, and this classification is still used to this day.
The autonomic nervous system includes both sensory pathways that send information from organs to the brain and motor pathways that send commands from the brain to organs. Sensory pathways convey information about the state of organs to the brain, allowing autonomic reflexes to occur.
structure
sympathetic nervous system
The sympathetic nervous system is often called the ‘battle mode nerve’. Nerves originate from the thoracic to lumbar areas of the spinal cord (1st thoracic to 2nd lumbar vertebrae). This nerve passes through a nerve relay station (ganglion) located next to or in front of the spine before reaching each organ.
In the front section of the sympathetic nervous system, a signaling substance called acetylcholine is used, and in the back section of the relay center, a signaling substance called norepinephrine is used. However, the sympathetic nerves that control the sweat glands use acetylcholine as an exception.
parasympathetic nervous system
The parasympathetic nervous system corresponds to the ‘recovery mode nerve’. Nerves originate from the brain stem and the sacral region of the spinal cord (sacral vertebrae 2 to 4). The parasympathetic nerve coming out of the brain stem travels along several cranial nerves, of which the vagus nerve transmits about 75% of parasympathetic nerve signals.
The parasympathetic nerve uses acetylcholine as a signaling substance in both the anterior and posterior segments of the relay station.
intestinal nervous system
The enteric nervous system is an independent neural network made up of more than 100 million nerve cells located in the walls of the digestive tract. It is called the ‘second brain’ because it can control the movement of the digestive tract, secretion of digestive juices, and blood flow on its own without commands from the brain.
function
cardiovascular regulation
The autonomic nervous system maintains appropriate blood pressure and blood flow by regulating heart rate, cardiac contraction force, and degree of blood vessel constriction. When the sympathetic nervous system is activated, the heart beats faster and harder and blood vessels narrow. Conversely, the parasympathetic nerve (vagus nerve) slows the heart rate.
When at rest, the heart is under constant inhibition from the vagus nerve, which is called vagal tone. Vagal tone can be measured indirectly by testing heart rate variability (HRV).
breathing control
The parasympathetic nerves narrow the bronchi, and the sympathetic nerves widen the bronchi. In airway hypersensitivity diseases such as asthma, excessive activity of the parasympathetic nervous system is involved.
digestive function
The parasympathetic nerve (vagus nerve) promotes gastric acid secretion, digestive enzyme secretion, and intestinal movement. Conversely, the sympathetic nerve suppresses digestive function and tightens the sphincter. The enteric nervous system coordinates the digestive process through its own reflexes, separate from these external nerve signals.
body temperature regulation
Sweat secretion, changes in skin blood flow, and contraction of the erector pilonidal muscle are key mechanisms for regulating body temperature. In a hot environment, the sympathetic nerve stimulates sweat glands to release sweat and expands skin blood vessels to dissipate heat.
Symptoms of autonomic nervous system abnormalities
When the balance of the autonomic nervous system is broken, various symptoms appear across multiple organs. This condition is called autonomic dysfunction.
Typical symptoms are as follows:
- Cardiovascular system: palpitations, dizziness when standing up (orthostatic hypotension), sudden fainting (syncope)
- Digestive system: heartburn, indigestion, constipation or diarrhea
- Temperature/sweating: Cold hands and feet, excessive sweating, abnormal body temperature regulation
- Urinary system: frequent urination, feeling of residual urination
- Systemic symptoms: chronic fatigue, sleep disturbance, difficulty concentrating.
Postural orthostatic tachycardia syndrome (POTS) is a representative autonomic disease in which the heart rate rapidly increases to more than 30 beats per minute when standing up.
Inspection method
Representative tests to evaluate autonomic function are as follows.
- Heart rate variability (HRV) analysis: This is a non-invasive test that determines the state of autonomic nervous system balance by analyzing minute changes in heartbeat intervals. According to the 1996 European Society of Cardiology standards, an SDNN of less than 100ms suggests a decline in autonomic function.
- Standing tilt table test: The patient is fixed to the bed and tilted to observe changes in blood pressure and heart rate.
- Valsalva maneuver: Analyze blood pressure and heart rate responses after holding your breath and exerting force.
- Deep breathing test: Measures heart rate changes due to deep breathing.
- Perspiration function test: Evaluates sweat secretion ability to check for autonomic nervous system abnormalities.
life management
Daily management rules to maintain autonomic balance are as follows.
- Regular aerobic exercise: Walking, swimming, or cycling for more than 30 minutes, 3 to 5 times a week, helps improve parasympathetic nerve function.
- Sufficient sleep: Regular sleep of 7 to 8 hours a day is essential for autonomic recovery.
- Stress management: Overactivation of the sympathetic nervous system can be suppressed through abdominal breathing, meditation, and relaxation training.
- Balanced diet: Reduce excessive caffeine and alcohol intake and drink plenty of fluids.
- Be careful of sudden changes in posture: If you have orthostatic symptoms, stand up slowly and avoid standing for long periods of time.
If chronic stress, lack of sleep, and irregular lifestyle continue, overactivation of the sympathetic nervous system may become established and various symptoms of autonomic abnormalities may appear. If symptoms persist, it is recommended to consult a specialist.