Name: 副交感神經系統。速成班A&P #15 (Parasympathetic Nervous System: Crash Course A&P #15)
Uploaded: 2021-01-14T05:32:14.000Z
Duration: 10 min 17 s
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情態副詞

For the average person -- at rest, like you probably are, sitting there watching me -- the

heart beats at around 60 beats per minute.

But if you were to somehow disconnect your heart from your autonomic nervous system,

things, as you might imagine, would change.

But, your heart would not stop. Actually, it would be the opposite.

It would start beating at around 100 beats per minute -- and that’s just at rest.

With your heart beating two-thirds faster than normal, before you even broke a sweat,

your cardiac muscle would experience a lot of extra wear and tear. The surrounding blood

vessels would be under enormous pressure. And your body would suddenly require -- and

Part of what keeps your heart under control is your parasympathetic nervous system.

It’s often described as the calming side of your autonomic system -- a kind of antidote

to the effects of stress created by the sympathetic system.

Unlike your sympathetic division, which lets you deal with the crisis of the now, the parasympathetic

system allows your body to handle … everything else.

It not only calms you down after being stressed out, it’s what allows you to digest food,

to reproduce, to excrete waste, to fight off infections.

Basically, it lets you do the business of living.

But our bodies can only do that when they are in balance, somewhere between excitement

and inhibition, both aroused enough and calm enough to keep things working.

So the parasympathetic system is why our hearts don’t pump so hard that they explode, sure.

But it also explains a lot of other stuff about our bodies.

Learning about the parasympathetic system is going to involve a lot of memorizing.

You will recall that our sympathetic & parasympathetic systems not only have different functions

-- more or less engaging the same organs to opposite effects -- they also have different structures.

Their ganglia, for example, are located in different places: The sympathetic ganglia

are located near the spinal cord, while on the parasympathetic side, they’re close to the effectors.

And likewise, the use of neurotransmitters in the two systems is similar, but not quite the same.

In both systems, neurons release acetylcholine, or ACh, in their preganglionic synapses.

But in your parasympathetic system, the postganglionic neurons release ACh at their synapses with

...as opposed to in the sympathetic system, where effectors get a dose of norepinephrine instead.

But the biggest anatomical difference between these two systems has to do with the physical

networks that they form as they reach throughout your body.

While the sympathetic nerves all spring from the thoracolumbar area of your spinal cord,

right around your midsection, the nerves of the parasympathetic division are craniosacral.

And with the exception of a couple of sacral nerves near the tailbone that run to the bladder

and genitals and rectum, most of these nerves never go through the spinal cord.

Instead, they run right from the brain almost all the way to their effectors.

There are 12 of these cranial nerves, and they vary in terms of what kinds of neurons they contain.

I mean, we’re talking about the autonomic system here, but they are not all autonomic motor fibers.

Some of your cranial nerves also carry motor fibers that control voluntary functions, like

And others carry only sensory fibers, which relay data to and from your sensory organs.

And, you know, just to keep things interesting, some of your cranial nerves carry both motor

So, which ones are where? And what exactly does each one of these 12 nerves do?

As anatomists, we have to keep track of the human wiring-diagram that are cranial nerves,

because you don’t want to end up like some sidekick in a ‘90s action movie who has

SHOULD I CUT THE RED WIRE OR THE BLACK WIRE?

Honestly, though, if you find yourself inside of somebody’s brain stem you probably shouldn’t

Since all 12 of these cranial nerves are important, you’re gonna have to come up with some kind

of mnemonics to help you keep track of both their names and their functions.

You’ll need to know what each one is called, whether it’s a sensory nerve, a motor nerve, or both.

And the map that we follow of the cranial nerves is based on a ventral view of the brain

-- looking at its underside, with the anterior portion at the top, and posterior on the bottom.

Starting at the top, the first cranial nerve you encounter is the olfactory nerve, which

takes scent information gathered by the nose and sends it to the brain.

Followed by the optic nerve, which does the same, but with visual data.

Then there’s oculomotor, which controls four of the six muscles that control the movements of your eyes.

The next nerve, near the center of the brain’s ventral side, is the trochlear nerve, which

controls a single muscle in the eye, and it lets you do this.

Just below that is the trigeminal nerve, the largest of the cranial nerves, which branches

into three main strands -- hence the ‘tri’ -- and innervates the face and jaw muscles.

After that there’s the abducens, which stimulates the muscles that let your eyes do this -- from

side to side, followed by the facial nerve, which operates the muscles that make most

Then there’s the auditory nerve. You can probably guess what that’s for.

You might notice that, up until the auditory nerve, the cranial nerves mostly control organs

in the front of the cranium -- mainly the eyes and facial muscles.

But as you work your way down, the nerves tend to innervate the lower and more posterior

Like the glossopharyngeal nerve, which leads to your tongue and your pharynx.

That’s followed by your vagus nerve -- you should definitely remember that one -- and

then the spinal accessory nerve -- which has to do with moving your head and shoulders,

and not whether your belt matches your shoes.

Lastly there’s the hypoglossal, the nerve that allows you to swallow and talk, among

other things that you do with your mouth and tongue.

That was a lot of information and probably new words, so how are you gonna remember it all?

Well, by finding a way to remember the first letter of each name, in order. Which is:

That doesn’t spell anything useful at all. There is a mnemonic that you’ll probably

On old Olympus’ towering top, a Fin and German viewed some hops.

That’s pretty weird sounding -- not terribly easy to remember. I mean, Olympus? Fin? Hops?

There’s gotta be something more relevant to us 21st century science lovers. Like, the

Lord of the Rings fans out there might prefer something along the lines of:

Onward old orcs! Toward the Argonath for a Great Villain! Slay Hobbits!

Whatever device you use to remember the names of the cranial nerves, you also have to keep