Sympathetic nervous system

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Sympathetic nervous system


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Sympathetic nervous system

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Bronchodilation p. 712

sympathetic receptors and p. 239


sympathetic receptors and p. 239

Renal sympathetic discharge p. 612

Renin p. 612

sympathetic receptors and p. 239

Sympathetic activity

venous return and p. 293

Sympathetic nervous system p. 237

male sexual response p. 651

Sympathetic receptors p. 237


sympathetic receptors p. 239


The nervous system is divided into the central nervous system, so the brain and spinal cord, and the peripheral nervous system, which includes all the nerves that connect the central nervous system to the muscles and organs.

The peripheral nervous system can be divided into the somatic nervous system, which controls voluntary movement of our skeletal muscles, and the autonomic nervous system, which is further divided into the sympathetic and the parasympathetic, and controls the involuntary movement of the smooth muscles and glands of our organs.

The sympathetic and parasympathetic nervous systems have opposite effects on the body.

The sympathetic nervous system controls functions like increasing the heart rate and blood pressure, as well as slowing digestion. All of this maximizes blood flow to the muscles and brain, and can help you either run away from a threat or fight it, which is why it’s also called the fight-or-flight response.

The parasympathetic nervous system instead slows the heart rate and stimulates digestion - the effects can be summarized as 'rest and digest'.

Now, neurons are the main cells of the nervous system. They’re composed of a cell body, which contains all the cell’s organelles, and nerve fibers, which are projections that extend out from the neuron cell body.


The sympathetic nervous system is a part of the autonomic nervous system (ANS) that helps regulate the body's involuntary functions such as breathing, digestion, heart rate, and blood pressure. It is based on a preganglionic or cholinergic neuron that releases acetylcholine and a postganglionic neuron that releases either catecholamines or acetylcholine to a target cell.

The sympathetic nervous system is often referred to as the fight or flight system because it helps prepare the body for action in response to a threatening or stressful situation. In emergency situations, the activity of the sympathetic nervous system increases and diverts blood away from the organs that are not necessary for survival, like the gastrointestinal tract and the bladder, and increases blood flow to muscles and organs like the brain. The sympathetic nervous system works in opposition to the parasympathetic nervous system, which helps the body to relax and conserve energy.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Adrenoceptor Function and Expression in Bladder Urothelium and Lamina Propria" Urology (2013)
  6. "The Sympathetic Nervous System in Heart Failure" Journal of the American College of Cardiology (2009)

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