The sympathetic nervous system is an essential part of the autonomic nervous system, responsible for regulating the body's internal organs and their functions. It is involved in the body's response to stress and emergencies, often referred to as the "fight or flight" response. This article will discuss the anatomy and function of the sympathetic nervous system.

Anatomy of the Sympathetic Nervous System

The sympathetic nervous system consists of a network of neurons that originate in the spinal cord and extend throughout the body. The cell bodies of the sympathetic neurons are located in the lateral horn of the spinal cord between T1 and L2 vertebrae. These neurons extend out from the spinal cord as preganglionic fibers, which synapse with postganglionic fibers in ganglia outside the spinal cord. The postganglionic fibers then extend to their target organs.

Scheme depicting which organs are controled by the sympathetic nervous system. The sympathetic nervous system is part of the autonomous nervous system. It extends from the brain (from the pons region at the top of the image) and travels down the spinal cord. At several instances, branches come out of the spinal cord to form the spinal nerves. These nerves innervate the bodily organs. BruceBlaus. Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436., CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons 

There are two types of ganglia in the sympathetic nervous system: the sympathetic chain ganglia and the collateral ganglia. The sympathetic chain ganglia are located on either side of the spinal cord and extend from the base of the skull to the coccyx. The collateral ganglia are located outside the sympathetic chain and include the celiac ganglion, superior mesenteric ganglion, and inferior mesenteric ganglion.

The sympathetic nervous system also has two major adrenal glands located on top of the kidneys. These glands release adrenaline (epinephrine) and noradrenaline (norepineprhine), which are hormones that enhance the body's response to stress.

Function of the Sympathetic Nervous System

The sympathetic nervous system is responsible for the body's response to stress and emergencies. It prepares the body for action, often referred to as the "fight or flight" response. When the sympathetic nervous system is activated, it causes several physiological changes in the body that you may recognize if you have read our article on the symptoms of stress. They are brought about by adrenaline (epinephrine) and include:

  1. Increased heart rate: The sympathetic nervous system increases heart rate by increasing the rate of contraction of the heart muscle. This increase in heart rate helps to pump more blood to the muscles, providing them with the energy needed to respond to a stressful situation.
  2. Dilated pupils: The sympathetic nervous system causes the pupils to dilate, allowing more light to enter the eye. This improves vision in low light conditions and helps the body to better detect potential threats.
  3. Bronchodilation: The sympathetic nervous system causes the bronchi in the lungs to dilate, increasing the amount of oxygen that can be taken in with each breath. This helps to provide the body with the energy it needs to respond to a stressful situation.
  4. Increased blood pressure: The sympathetic nervous system increases blood pressure by causing the blood vessels to constrict. This helps to increase blood flow to the muscles, providing them with the energy needed to respond to a stressful situation.
  5. Elevated blood sugar: The sympathetic nervous system increases blood sugar levels by stimulating the release of glucose from the liver. This provides the body with the energy it needs to respond to a stressful situation.
  6. Reduced digestive activity: The sympathetic nervous system reduces digestive activity by decreasing blood flow to the digestive organs. This helps to redirect blood flow to the muscles, providing them with the energy needed to respond to a stressful situation.
  7. Increased sweat production: The sympathetic nervous system increases sweat production, which helps to regulate body temperature during periods of increased physical activity.
  8. Constriction of blood vessels: The sympathetic nervous system causes the blood vessels to constrict, reducing blood flow to non-essential organs such as the skin, digestive system, and kidneys. This helps to redirect blood flow to the muscles, providing them with the energy needed to respond to a stressful situation.
  9. Increased blood flow to muscles: The sympathetic nervous system increases blood flow to the muscles, providing them with the energy needed to respond to a stressful situation. This is achieved by the vasodilation of the blood vessels that supply the muscles.
  10. Suppression of immune system: The sympathetic nervous system suppresses the immune system by reducing the production of immune cells. This helps to prioritize energy towards the "fight or flight" response, which takes precedence over immune system activity.

Overall, the sympathetic nervous system prepares the body for immediate action in response to a perceived threat or emergency. It activates the body's fight or flight response, which allows an individual to quickly respond to a potentially dangerous situation.

Dysfunction of the Sympathetic Nervous System

Dysfunction of the sympathetic nervous system can lead to various disorders. Some of these disorders include:

  1. Autonomic Dysfunction: Autonomic dysfunction is a disorder that affects the autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems. This disorder can cause a range of symptoms, including dizziness, rapid heartbeat, and abnormal sweating.
  2. Hyperhidrosis: Hyperhidrosis is a disorder that causes excessive sweating, often in response to stress or anxiety. This disorder can be caused by dysfunction of the sympathetic nervous system.
  3. Raynaud's Disease: Raynaud's disease is a disorder that causes the blood vessels in the fingers and toes to constrict in response to cold temperatures or stress. This disorder can be caused by dysfunction of the sympathetic nervous system.
  4. Hypertension: Hypertension, or high blood pressure, can be caused by dysfunction of the sympathetic nervous system. This is because the sympathetic nervous system can cause the blood vessels to constrict, increasing blood pressure.

Takehome message about the sympathetic nervous system

The sympathetic nervous system is an essential part of the autonomic nervous system. It is responsible for the body's response to stress and emergencies, often referred to as the "fight or flight" response. The sympathetic nervous system prepares the body for immediate action by increasing heart rate, dilating pupils, increasing blood pressure, and increasing blood sugar levels. Dysfunction of the sympathetic nervous system can lead to various disorders, including autonomic dysfunction, hyperhidrosis, Raynaud's disease, and hypertension.

Cover image: http://www.scientificanimations.com, CC BY-SA 4.0

https://creativecommons.org/licencses/by-sa/4.0, via Wikimedia Commons