Autonomic Nervous System: Sympathetic vs Parasympathetic, Animation

(USMLE topics, nervous system) The divisions of the ANS: Sympathetic, SNS, versus parasympathetic, PSNS.
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The autonomic nervous system, or ANS, is the part of the nervous system that regulates activities of internal organs. The ANS is largely AUTONOMOUS, acting independently of the body’s consciousness and voluntary control. It has two main divisions: sympathetic, SNS, and parasympathetic, PSNS.
In situations that require alertness and energy, such as facing danger or doing physical activities, the ANS activates its sympathetic division to mobilize the body for action. This division INcreases cardiac output, accelerates respiratory rate, releases stored energy, and dilates pupils. At the same time, it also inhibits body processes that are less important in emergencies, such as digestion and urination.
On the other hand, during ordinary situations, the parasympathetic division conserves and restores. It slows heartbeats, decreases respiratory rate, stimulates digestion, removes waste and stores energy.
The sympathetic division is therefore known as the “fight or flight” response, while the parasympathetic division is associated with the “rest and digest” state.
Despite having opposite effects on the same organ, the SNS and PSNS are NOT mutually exclusive. In most organs, both systems are simultaneously active, producing a background rate of activity called the “autonomic tone” - a balance between sympathetic and parasympathetic inputs. This balance SHIFTS, one way or the other, in response to the body’s changing needs.
Some organs, however, receive inputs from ONLY ONE system. For example, the smooth muscles of blood vessels only receive sympathetic fibers, which keep them partially constricted and thus maintaining normal blood pressure. An increase in sympathetic firing rate causes further constriction and INcreases blood pressure, while a DEcrease in firing rate dilates blood vessels, lowering blood pressure.
The autonomic nerve pathways, from the control centers in the central nervous system to the target organs, are composed of 2 neurons, which meet and synapse in an autonomic ganglion. Accordingly, these neurons are called PREganglionic and POSTganglionic.
In the SNS, the preganglionic neurons arise from the thoracic and lumbar regions of the spinal cord; their fibers exit by way of spinal nerves to the nearby sympathetic chain of ganglia. Once in the chain, preganglionic fibers may follow any of 3 routes: some fibers synapse immediately with postganglionic neurons; some travel up or down the chain before synapsing; some pass through the chain without synapsing - this third group continues as splanchnic nerves to nearby collateral ganglia for synapsing instead. From the ganglia, LONG POSTganglionic fibers run all the way to target organs. The SNS has a high degree of neuronal DIVERGENCE: one preganglionic fiber can synapse with up to 20 postganglionic neurons. Thus, effects of the SNS tend to be WIDESPREAD.
In the PSNS, the preganglionic neurons arise from the brainstem and sacral region of the spinal cord. Preganglionic fibers exit the brainstem via several cranial nerves and exit the spinal cord via spinal nerves before forming the pelvic splanchnic nerves. Parasympathetic ganglia are located near or within target organs, so postganglionic fibers are relatively short. The degree of neuronal divergence in the PSNS is much lower than that of the SNS. Thus, the PSNS produces more SPECIFIC, LOCALIZED responses compared to the SNS.

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The dislikes are from people without PNS and it's ANS.

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thank you for clearing up the vasodilation/constriction thing i was confused when my teacher was teaching about it

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I am having the biology exam after 2 days. I'm in 8th grade and our teacher didn't explained it that well (Though she's very helpful), I was so confused between these 2 but now my doubts are clear. Thanks

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Thanks Alila Medical Media; those who are following my 'crumb trail' will find this useful . Basically disavow both ill intent attacks on these two systems. Joop Joop!

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Which release ACH, Norepinephrine and why would of fit in this video nicely

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If urine function decreases why do people wet themselves when scared.

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That has more to do with the valve that holds the bladder/urethra closed, when you are scared, you lose control of that valve.

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I realised the 7 chakra is located on these organs.. not specifically but its placement

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Thank you, very helpful

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Saying the autonomic system is responding to the body misses the more important half of being

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ive watched so many videos about sns but this one is the best

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why does acetylcholine (parasympathetic) cause WAKEFULLNESS. Shouldn't it make you sleepy instead?? Instead, it is the ANTI-cholinergics (like diphenhydramine) that make you sleepy. Counter-intuitive?

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Blood Fainting: *body switching between the sympathetic and parasympathetic systems*

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If the sympathetic nervous system comes into play during fight or flight situations why does it have shorter myelinated axons and longer post ganglionic unmyelinated axon? Since we already know that myelinated axons transmit impulses much faster shouldnt it be the other way around?

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Parasympathetic division

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Bruh both autonomic nervous systems work in harmony, they’re never activated nor deactivated just used more or less

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What is difference between involuntarily reflexes and involuntarily sympathetic action? For example how you determine that increas of heart beat is sympathetic but increase of secretion of salivia when seeing food us a reflex?

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Aren't those pre-ganglionic neurons Oligodendrocytes ?

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Amazing explanation. Liked. However one small confusion. As you say there are only 2 neurons (pre and post ganglionic) in between the CNS and the Effector organs, how it's possible for just two microscopic neurons to cover that distance? Please elaborate.

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Yeap, tiny neurons but they have very long axons. An average length of an axon is about 1 meter!

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@@Alilamedicalmedia So you mean the entire length from the spine to the digestive system can be covered by a single neuron?

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Yes, it's amazing. Same as those motor neurons that can extend from the spine all the way to your arms or legs! Of course there are also much shorter neurons, within the spinal cord or brain for example.

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I think the colour matching of the first diagram is a little bit confusing. It seems so that the Sympathetic Nervous System Up regulates the Digestion, which is not true at all. But besides that it is a very good video!

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