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The Parasympathetic Nervous System

The main nerves of the parasympathetic system is the tenth cranial nerve, the vagus nerves. They have their origin in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the lower part of the brain and spinal cord.

The main nerves of the parasympathetic system is the tenth cranial nerve, the vagus nerves.  They have their origin in the medulla oblongata.  Other preganglionic parasympathetic neurons also extend from the lower part of the brain and spinal cord.

Each neuron preganglionic parasympathetic neurons synapse with postganglionic few that are close to – or – the effector organ, muscle or gland.  Acetylcholine (ACH) is the neurotransmitter in all the above and most of the postganglionic parasympathetic neurons.  But some of the postganglionic neurons release nitric oxide (NO) as neurotransmitter.

The physiologist, Nobel laureate Otto Loewi discovered (in 1920) that the effect of stimulation of both sympathetic and parasympathetic mediated by chemicals released.  He took the beating heart of the frog, and the sympathetic and parasympathetic nerves intact.  As expected, stimulation of the initial acceleration of the heart, while stimulation of the other is slower.

Loewi discovered that these two reactions that occur in a frog’s heart comes with a second salt solution comes from the heart stimulated.  Electrical stimulation of the vagus nerve leading to the heart first, not only slowed the pace, but soon after, and the second heart slowed.  The substance responsible was later shown that acetylcholine.  During sympathetic stimulation, the adrenaline (frog) released.
parasympathetic stimulation causes

* Slow heart rate (as demonstrated by Loewi)
* Reduced blood pressure
* Constriction of pupils
* Increased blood flow to the skin and internal organs
* Gastro-intestinal peristalsis

In summary, parasympathetic system returns the body to function normally after being changed by sympathetic stimulation.  In times of danger, the sympathetic system prepares the body for violent activity.  The parasympathetic system reverses these changes when the danger is past.

Vagus nerve also helps to keep inflammation under control.  Inflammation stimulates sensory neurons near the vagus nerve.  When these nerve impulses when the medulla, which is relayed along the fibers of the motor to the inflamed area.  The acetylcholine from motor neurons suppresses the release of inflammatory cytokines such as tumor necrosis factor (TNF) in macrophages in inflamed tissue.

Although the autonomic nervous system is regarded as involuntary, it is not true.  A certain degree of conscious control can be exercised on him as it has been demonstrated by practitioners of yoga and Zen Buddhism.  During his periods of meditation, these people are clearly able to change a number of autonomic functions like heart rate and rate of oxygen consumption.  These changes are not simply a reflection of decreased physical activity due to exceeding the number of changes that occur during sleep or hypnosis.

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