Parasympathetic nervous system


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Parasympathetic nervous system

Nervous system

Anatomy and physiology

Nervous system anatomy and physiology

Neuron action potential

Cerebral circulation

Blood brain barrier

Cerebrospinal fluid

Cranial nerves

Ascending and descending spinal tracts

Somatic nervous system

Motor cortex

Pyramidal and extrapyramidal tracts

Muscle spindles and golgi tendon organs

Spinal cord reflexes

Sensory receptor function

Somatosensory receptors

Somatosensory pathways

Autonomic nervous system

Sympathetic nervous system

Adrenergic receptors

Parasympathetic nervous system

Cholinergic receptors

Enteric nervous system


Body temperature regulation (thermoregulation)

Hunger and satiety



Basal ganglia

Basal ganglia: Direct and indirect pathway of movement

Higher order brain functions










Parasympathetic nervous system


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Parasympathetic nervous system

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Parasympathetic nervous system p. 237

male erection p. 651

Parasympathetic receptors p. 237

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Content Reviewers

Rishi Desai, MD, MPH


Antonella Melani, MD

Sam Gillespie, BSc

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. These are either dendrites that receive signals from other neurons, or axons that send signals along to other neurons.


The parasympathetic nervous system is one of two divisions of the autonomic nervous system (ANS), the other being the sympathetic nervous system. The ANS controls the body's automatic or unconscious functions, such as heart rate, digestion, and breathing.

The activity of the parasympathetic nervous system can be summarized as �rest and digest' because it slows the heart rate and keeps the body's energy use as low as possible to stimulate organs like the gastrointestinal tract and the bladder.

In the parasympathetic nervous system, preganglionic cholinergic neurons release acetylcholine to activate postganglionic cholinergic neurons, which then release acetylcholine to target cells. Thus, their nerve fibers are referred to as cholinergic fibers.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Physiology of the Autonomic Nervous System" American Journal of Pharmaceutical Education (2007)
  6. "The sacral autonomic outflow is sympathetic" Science (2016)

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