Your sympathetic nervous system is one of the branches of your autonomic nervous system. It controls functions under unconscious control related to “fight or flight.”
Your nervous system plays a critical role in almost all bodily functions. Without it, you wouldn’t be able to think, move, or survive.
The autonomic nervous system (ANS) is the branch of your peripheral nervous system (PNS) that controls subconscious functions. It can be further broken down into two categories:
- Sympathetic nervous system: Carries out your body’s “fight or flight” functions
- Parasympathetic nervous system: Carries out your body’s “rest and digest” functions
Sympathetic nerve fibers exit your central nervous system and affect many of your major organs.
Read on to learn more about the sympathetic nervous system including what it does and what problems can affect it.
Your sympathetic nervous system is a network of nerves under involuntary control associated with your “fight or flight” response. It helps mobilize your body into action to protect itself from a perceived threat.
Nerve fibers from your sympathetic nervous system lead to almost every organ system in your body.
Activation of your sympathetic nervous system causes short-term changes to your body that occur alongside hormonal changes. Hormones generally have a slower but longer-lasting action than neurological signals.
Your sympathetic nervous system plays a vital role in helping your body respond to external stressors and threats. When activated, it triggers physiological changes to prepare your body for immediate action. Some
- increasing heart rate and blood pressure to allow more blood to reach your muscles and heart
- expanding airways to allow more air to flow into your lungs
- dilating your pupils to allow more light to enter
- reducing digestive activity to divert energy toward your muscles and vital organs
- reducing insulin secretion to give your body access to sugar in your blood
- increasing sweating to regulate body temperature during increased activity
Additionally, your sympathetic nervous system is constantly active even in non-stressful situations. It continuously works with your parasympathetic nervous system to dilate your airways during respiration, among other tasks.
Your sympathetic nervous system relies on specific neurotransmitters to transmit signals and coordinate its functions. The primary neurotransmitters involved are:
- Norepinephrine (noradrenaline): Norepinephrine is the main neurotransmitter of the sympathetic nervous system. It’s released by
postganglionic neurons , which are neurons leading to target organs. - Epinephrine (adrenaline): Epinephrine is
released by your adrenal glands into your bloodstream. It causes effects like increasing heart rate and boosting energy availability. - Acetylcholine: Acetylcholine is a neurotransmitter primarily associated with the parasympathetic nervous system. It’s also released by
preganglionic neurons in your sympathetic nervous system. These nerves have their cell bodies in yourspinal cord .
The sympathetic and parasympathetic nervous systems work together to regulate your body’s involuntary functions. The parasympathetic branch is primarily responsible for “rest and digest” functions.
These two branches of your nervous system tend to have
| Effect | Sympathetic effects | Parasympathetic effects |
|---|---|---|
| Heart rate | increases | decreases |
| Blood pressure | increases | decreases |
| Pupils | get bigger | get smaller |
| Sweating | increases | decreases |
| Digestive activity | decreases | increases |
Dysfunction of your sympathetic nervous system is associated with many medical conditions, including:
Heart disease
A variety of heart conditions can cause changes that lead to increased sympathetic and decreased parasympathetic activity to maintain heart function. These conditions may include:
Tumors
Some tumors like pheochromocytoma can increase the activity of your sympathetic nervous system by increasing the secretion of epinephrine and norepinephrine.
Genetic disorders
Some genetic disorders can cause dysautonomia, which is the improper function of your autonomic nervous system. These
- familial dysautonomia
- Fabry disease
- hereditary sensory autonomic neuropathy
- amyloidosis
Autoimmune conditions
Autoimmune
Spinal cord injuries
Hyperhidrosis (excessive sweating)
Hyperhidrosis is the medical name for excessive sweating. It may be treated in some cases by removing the nerves that tell your glands to produce sweat.
Anxiety and stress
Chronic stress and anxiety can lead to chronic overactivation of your sympathetic nervous system. This can lead to chronic changes like increased blood pressure and a rapid heart rate.
Problems with your sympathetic nervous system depend on the underlying condition with which you’re dealing. Symptoms and signs associated with overactivity of your sympathetic nervous system include:
- rapid or irregular heartbeat
- high or low blood pressure
- excessive sweating or lack of sweating
- dizziness or fainting
- difficulty regulating body temperature
- anxiety or heightened stress responses
- digestive issues, such as constipation or diarrhea
- sexual dysfunction
It’s important to see a doctor if you develop concerning symptoms, such as:
- persistent dizziness or fainting
- severe fluctuations in blood pressure
- unexplained rapid heart rate or palpitations
- difficulty breathing
- chest pain
- unusual sweating
- chronic digestive problems
If you believe you may have a sympathetic nervous system problem, the first tests your doctor will likely perform include:
- review of your personal and family medical history
- review of your symptoms
- physical exam
If your doctor thinks you may have a nervous system problem, you may receive additional testing, such as:
- electrocardiogram (EKG)
- electroencephalogram
- blood pressure test
- blood tests
- genetic tests
- imaging, such as MRI
- a series of tests called autonomic nervous system testing
Treatment for sympatric nervous system disorders depends on the specific condition.
Making lifestyle improvements may help support your overall health and conditions, such as anxiety or chronic stress. Lifestyle changes you can make include:
- eating a balanced diet
- eating small, frequent meals
- minimizing or avoiding illegal drugs, alcohol, and smoking (quitting can be difficult, but a doctor can build a plan that works for you)
- exercising regularly
- scheduling time for stress-relieving activities
- getting plenty of sleep
- wearing compression socks and other garments to maintain blood pressure
Other conditions may need additional treatment, such as:
- medications or procedures for heart conditions
- surgery and emergency treatment for spinal injuries
- surgery for excessive sweating
- medications for autoimmune conditions
- chemotherapy, radiation therapy, or other cancer treatments
Your sympathetic nervous system is under subconscious control. It’s responsible for your body’s fight-or-flight response.
In general, your sympathetic nervous system makes energy more available. Problems with your sympathetic nervous system can cause changes like a rapid heart rate, high blood pressure, or digestive problems.