On This Page:ToggleFunctionNervesNeurotransmittersOver and under-activation of the SNSCalming down the SNS
On This Page:Toggle
On This Page:
The sympathetic nervous system (SNS) is one of two main divisions of theautonomic nervous system, which controls involuntary body processes.
The SNS activates what is often termed the “fight or flight” response. When the body perceives a threat, the SNS stimulates bodily responses that serve to prepare the body for actionin response to dangerrapidly.
Sympathetic vs. parasympathetic nervous systemThe SNS works in opposition to theparasympathetic nervous system(PNS), which governs the “rest and digest” functions to conserve energy.The parasympathetic branch stimulates digestion and the urinary system when relaxed, whereas the SNS slows them down as these processes are not required during heightened stress.Theneuronsof the SNS also haveshorter pathwaysthan those of the parasympathetic nervous system.This shorter distance allows for a quicker signal transmission; sometimes the responses happen before a person is consciously aware of them.Together, the SNS and PNS work tomaintain homeostasisin the body (the balance of internal physiological mechanisms).
Sympathetic vs. parasympathetic nervous system
The SNS works in opposition to theparasympathetic nervous system(PNS), which governs the “rest and digest” functions to conserve energy.
The parasympathetic branch stimulates digestion and the urinary system when relaxed, whereas the SNS slows them down as these processes are not required during heightened stress.
Theneuronsof the SNS also haveshorter pathwaysthan those of the parasympathetic nervous system.
This shorter distance allows for a quicker signal transmission; sometimes the responses happen before a person is consciously aware of them.
Together, the SNS and PNS work tomaintain homeostasisin the body (the balance of internal physiological mechanisms).
What does the SNS do?
1. Fight-or-flight response
The primary function of the SNS is to activate thefight-or-flight responsein threatening or stressful situations. When activated, the SNS can cause the following physiological responses:
These above effects can help in situations where you need to think and act quickly.
In this situation, your SNS may cause your heartbeat to quicken, you might start sweating, and you may become more alert to your surroundings.
These responses to a threatening situation areessential for survival. In evolutionary terms, the SNS would have been used to fight or escape predators and for hunting to eat and survive.
In modern-day, any stressor, even if not life-threatening, can trigger the fight-or-flight response. Examples include financial and work stress, taking a school exam, or even asking someone out on a date.
2. Regulating Body Temperature
For homeostasis to be achieved, the SNS cancontrol the body temperatureof organisms through the use of fat reserves in the body.
The SNS uses these reserves to increase heat production and change blood flow to the skin.
The SNS is also able to stimulate the sweat glands to enable the body to cool down, as well as being able tostimulate fatty acid releaseto instigate long-term responses to persistent periods of cold.
3. Cardiovascular Effects
The SNS can have effects on the cardiovascular system within the body.
This comes into play when exercising (when heart rate needs to increase), changing posture (e.g., sitting to standing), andtransitioning from sleep to wakefulness.
These changes via the SNS are necessary, especially when changing positions; otherwise, this can cause dizziness and fainting.
Nerves of the SNS
The SNS consists of neurons found within theperipheral nervous systemand the central nervous system, which usually work to stimulate the body’s organs in response to fear or stress.
The two types of neurons within the sympathetic nervous system arepreganglionic and postganglionic neurons or ganglion cells. (‘Ganglia’ refers to clusters of neurons outside the brain and spinal cord.)
The preganglionic neurons originate in thebrain stem or spinal cordand will always leave the spinal cord through areas called the thoracic and lumbar regions.
They will then synapse with the postganglionic neurons and will then extend to target organs of the SNS (e.g., heart, sweat glands, and stomach) to trigger certain effects when activated.
Neurotransmitters in the SNS
The SNS uses neurotransmitters to communicate.Neurotransmitters are the chemical messengerswhich are transmitted through neurons.
These neurotransmitters are:
As a result, these neurotransmitters encourage the body’s organs involved in the SNS to respond to a threat.
Over and under-activation of the SNS
If the SNS is activated too frequently, this can have long-lasting effects on the body, resulting inchronic stress.
Similarly, constant surges of epinephrine can damage blood vessels and arteries, which in turn can increase blood pressure and increase the risk of strokes and heart attacks.
Alternatively, if the SNS is under-functioning, this can also cause issues. If someone’s SNS is not functioning, theymay not respond appropriately in times of stress.
As their organs are not receiving signals to fight-or-flight, they may beunder-preparedin these situations, due to lack of blood being pumped around the body or other systems failing to be recruited.
Anxiety disorders, such as generalized anxiety disorder (GAD) andpanic disorder, involveoveractivation of the SNS.
In anxiety disorders, the SNS responds to non-threatening situations as if they were life-threatening, causing excessive fear and worry which can be very distressing.
Calming down the SNS
If you find yourself with an overactive SNS in situations that aren’t life-threatening, there are several strategies you can use to helpcalm your body’s stress response:
Remember, everyone responds to stress differently, so it may take some experimentation to find the strategies that work best for you.
Consistently incorporating these techniques into your daily routine can help improve your body’s ability to manage stress and regulate SNS activity over time.
References
Alshak, M. N. (2019). Neuroanatomy, sympathetic nervous system.
Biology Dictionary. (October 4, 2019). Sympathetic Nervous System. https://biologydictionary.net/sympathetic-nervous-system/
Lumen. (n.d.). Functions of the Autonomic Nervous System. Retrieved May 5, 2021 from https://courses.lumenlearning.com/boundless-ap/chapter/functions-of-the-autonomic-nervous-system/
Karina Ascunce GonzálezNeuroscience B.A. (Hons), Harvard UniversityPhD Neuroscience Student, Yale University
Karina Ascunce González
Neuroscience B.A. (Hons), Harvard University
PhD Neuroscience Student, Yale University
PhD Student at the Yale Biological & Biomedical Sciences' Interdepartmental Neuroscience Program interested in neurodegeneration, stem cell culture, and bioethics. AB in Neuroscience with a Secondary in Global Health & Health Policy from Harvard University. Karina has been published in peer reviewed journals.
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
