Pratique du Shadowing: Embryology of the Nervous System - Apprendre l'anglais à l'oral avec la vidéo

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In this video, we'll talk about nervous system embryology.

Let's get started.

The important thing to note here is that you have something called a blastula, and over time, that blastula will sort of fold into itself, shown here in red.

In doing so, the blastula will give rise to a blastopor.

For the purposes of nervous system embryology, we don't really care about the blastopor because that goes on to form a cavity for the GI system.

But what we do care about is that after the blastula folds into itself, we get the formation of three germ layers.

Those three germ layers are the endoderm, the mesoderm, and the ectoderm.

And in talking about nervous system embryology, we are particularly focused on the ectoderm.

The ectoderm is what goes on to become the entire nervous system.

So here's where we are right now.

We've got an ectoderm shown in purple, mesoderm shown in orange, and I'm not even showing you the endoderm

because it's kind of irrelevant for the purposes of this embryology discussion.

So between where the mesoderm sits, you get the development of something called the nodochord.

And the nodochord will secrete growth factors, and those growth factors will seep out and act on the ectoderm.

Those growth factors are going to tell the ectoderm to start to differentiate into a neural plate.

Now, as that neural plate begins to form in the center, it pushes out the ectoderm laterally.

The combination of the ectoderm moving laterally and the growing neural plate forming in the medial section,

this is all referred to as the neuroectoderm because the ectoderm is giving rise to all of the nervous system.

Now, what's going to start to happen here is that the neural plate will sort of start to fold over.

And as it grows and continues to fold, it's going to push the ectoderm up and out.

And it's going to look like this.

So that growing, if we were on this side, that growing neural plate starts to fold.

And then the ectoderm forms these folds that will curve out at the top.

Now between the ectoderm, which is shown in purple and is continually moving out laterally and folding over.

And the neural plate, which is shown in teal, which is growing in a sort of circular fashion,

that area in between them shown here with the brown circles, that is going to ultimately give rise to neural crest.

So again, in teal, we have neural plate.

In brown, we have the tissue that will ultimately become neural crest.

And in purple, we have the ectoderm that's folding out laterally, and this is referred to as the neural folds.

Now as these neural folds start to invaginate, they sort of pinch medially,

and as this happens, the neural plate area of the neural folds will move toward the midline.

And so when all of these motions are happening in 3D in real time, you're slowly going to get the formation of a circular object.

And what we end up with is a neural tube, which was derived from the neural plate, the neural crest, which sits right above it,

which was the area in between the ectoderm of the neural fold and the neural plate of the neural fold.

And then we've got the remnants of the ectoderm up on the top.

And so this entire process that I've just described is what's known as neurulation.

And on your exams, neurulation is is really the meat of all of your questions.

So if they're going to ask you a black

and white question about embryology in terms of how these things are folding and moving, it's probably going to be about neuralation.

So here's where we are.

And let's pause for a moment

because what becomes really high yield is not only knowing how

neuralation works in terms of the neural ectoderm giving rise to the neural crest and the neural tube,

but also pathology that can occur if this doesn't happen the way that it's supposed to.

So embryology, if you want to really be a reductionist here

and think about this in a really simple and stupid kind of way.

Embryology is normal, but when embryology doesn't occur normally, you get pathology and congenital abnormalities.

So let's talk about spina bifida.

Spina bifida in general refers to varying degrees of congenital abnormalities

that result from the failure of the neural tube to close caudally.

In other words, if neuralation, as I've just described it, doesn't occur the way that it's supposed to, one of the manifestations of that is spina bifida.

So let's go and talk about the three different types of spina bifida.

We'll start with spina bifida occulta.

Spina bifida occulta, there is no protrusion of spinal contents.

Okay, so look at the image below.

There's three different types of spina bifida.

There's spina bifida occulta, spina bifida with meningocele, and spina bifida with myelomeningocele.

And as you move from left to right across these three different types, it gets more severe.

So in spina bifida occulta, no protrusion of the spinal contents will be coming out through the vertebrae.

And in this case, alpha fetal protein, when it's measured, will be normal.

You would only see elevated levels of alpha fetal protein

if there is an open hole in the low back through the vertebrae, because that's where the AFP will leak out, and that's where it's measured.

Now in these patients with spina bifida occulta, you could see a tuft of hair or a sacral dimple right in

that area of the low back where in more severe versions of spina bifida, you would see protrusion.

But again, in occulta, it's called occulta because it's occult.

You don't see it.

It's kind of there hidden with no protrusion.

So this is the most benign version of spina bifida.

Now in spina bifida with meninges seal, we do see protrusion of the meninges.

And because we're seeing protrusion and because there's that opening in the low back, levels of alpha-fetoprotein will be increased if measured.

And in these patients, the spinal cord is undamaged.

And that's important to know because even though you have protrusion of something, it's just the meninges.

It's not the spinal cord itself.

So look in the image, the spinal cord is still in the canal where it's supposed to be.

It's just the meninges that are protruding through.

Lastly, we have spina bifida with myelomeningocele.

And this is the most severe type of spina bifida.

In myelomeningocele, you see protrusion of both the meninges and the spinal cord.

And because of this, because there's a hole in the low back, fluid can leak out.

So if measured, you'll see increased levels of alpha-feta protein.

What's very important to know for exams is that spina bifida with myelomeningocele is highly associated with Chiari type 2 malformations.

Now these are the three different types of spina bifida, and I want to show you this summary chart so that you can keep all of this straight.

Again, occulta is occult.

It's not protruding through.

It's just there in the low back.

So there's no protrusion and AFP is normal.

In these patients, you could see a tuft of hair or sacral dimpling.

In spina bifida with meninges, it's meninges.

It's just meninges.

So protrusion of the meninges through the low back, there's a hole there, so AFP will be increased.

It's just meninges, so the spinal cord is fine.

It's just the meninges.

In spina bifida with myelomeningocele, it's myeloplus meningoceles.

So So it's spinal cord, mylo, plus meningo, plus meninges.

So it's protrusion of meninges and spinal cord.

There's a hole in the low back, so AFP is increased.

And this is highly associated with Chiari 2 malformations.

So these are the three different types of spina bifida.

Again, this pathology occurs if neurulation does not happen normally.

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The other pathology I want to talk about is anencephaly.

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And this is a really sad and unfortunate congenital malformation where you have partial absence of the brain,

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calvaria, or skull because the neural tube didn't close at the cephalic end.

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So spina bifida is at the other end, not the cephalic end.

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But anencephaly is the cephalic end, right?

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So it's up at the top where the head would be.

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So in anencephaly, you can, you really see incompatible with life, right?

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So this isn't compatible with survival.

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If, if, if a developing baby has anencephaly, then unfortunately it's, it's either going to be stillborn or it will probably pass within a few hours of birth.

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And in anencephaly, you're going to see increased levels of AFP and polyhydramnios.

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Again, there's a hole up where the head should be, and that allows the leakage of fluid.

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So we'll the increased AFP and polyhydramnios.

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Now again, this is what we were talking about.

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So we were talking about neurulation and this is where we ended.

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And what's important to note now is that at that neural tube, at the top of the neural tube where that black star is shown,

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this is what's going to lead to primary vesicle formation.

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So let's talk about that now.

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So primary vesicle formation is the formation of the developing nervous system.

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And the first thing that's going to form are three primary vesicles.

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So we have the prosencephalon, which gives rise to the forebrain, the mesencephalon, which gives rise to the midbrain,

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and the romencephalon, which gives rise to the hindbrain.

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Again, all of this is derived from the top part of the neural tube.

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Now each of these three areas shown in different colors for your convenience gives rise to more and more structures.

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So the prosencephalon will give rise to both the telencephalon and the diencephalon.

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The mesencephalon will give rise to the mesencephalon, so that's pretty easy to memorize.

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The romencephalon will give rise to both the metencephalon and the myelencephalon.

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Now, I'm going to pause for a moment.

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I have another video on my channel that goes through this and gives you mnemonics to remember all of this.

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So I'm just describing the embryology here, but if you want the mnemonic for how all of this is easily memorized, then see that other video.

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So now we have the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon.

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And these are going to give rise to neural derivatives, okay?

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So just to keep things stupid and simple, we talked about these are your primary vesicles.

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They give rise to secondary vesicles.

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Here are your secondary vesicles that will give rise to neural derivatives, okay?

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So the telencephalon will give rise to the cerebral hemispheres and the globus pallidus, and the diencephalon will give rise to the thalamus and the hypothalamus.

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The mesencephalon, the metencephalon, and the myelencephalon give rise to midbrain, pons, cerebellum, and medulla.

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And if you're a little confused right now in terms of how you're supposed to learn all of this

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and keep all of this straight, aside from using my mnemonic, which I have in my other video on this topic.

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Really, if you know neuroanatomy, this should make sense because the telencephalon is at the top, the myelencephalon is at the very bottom,

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and then you've got varying degrees of these vesicles in between.

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And so from top down, if you know where the cerebral hemispheres are, where the globus pallidus is, thalamus, hypothalamus, as I go down this list,

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et cetera, et cetera, I'm moving from top to bottom.

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So if you know that the telencephalon is at the top and the myelencephalon is at the bottom, and then you're asked which one gives rise to the medulla, well, in your head, you could be like,

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I know that the medulla is at the bottom or the base of the brain.

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So which of the secondary vesicles is at the bottom or is at the base?

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And so myelencephalon gives rise to medulla.

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Conversely, if you're asked what gives rise to the cerebral hemispheres, in your head you could be like,

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well, I know that the cerebral hemispheres are sort of like at the outside or at the top of the brain,

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and so it's probably the topmost secondary vesicle, so it's probably telencephalon.

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And so it's easier to guess if you have a rough idea of the general neuroanatomy from top to bottom.

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And that's a theme that we'll carry over into the next slide as well.

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So these neural derivatives each give rise to cavities or where CFS or CSF flows.

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That's a tongue twister.

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So the telencephalon goes to cerebral hemispheres and globus pallidus.

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That gives rise to the lateral ventricle.

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The diencephalon gives rise to the thalamus and hypothalamus.

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That gives rise to the third ventricle.

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Mesencephalon gives rise to midbrain that creates the cerebral aqueduct.

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Metencephalon, pond cerebellum, that gives rise to the upper part of the fourth ventricle.

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And the myelencephalon gives rise to the medulla, that gives rise to the lower part of the fourth ventricle and the central canal.

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So just like we saw with the neural derivatives, if you have a rough understanding of top to bottom neural anatomy,

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you can make a very educated guess about which ventricle or which cavity is formed from which structure.

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And so here is an image of how CSF flows from top to bottom.

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So lateral ventricle to third ventricle to cerebral aqueduct to fourth ventricle to central canal.

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And top to bottom, you see on this slide, it's identical to this slide.

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So telencephalon at top, then diencephalon, mesencephalon, metencephalon, myelencephalon, top to bottom.

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And so keeping this color coded top to bottom, we go lateral to third, cerebral, fourth, central.

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Again, the takeaway here is that you can either memorize it, you can learn a mnemonic from my other video,

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or you can just, if you know neuroanatomy, work top to bottom.

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And this should all make sense.

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So those are the derivatives.

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So here's what we talked about.

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The top part of the neural tube gave rise to primitive vesicles or primary vesicles.

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Those gave rise to secondary vesicles.

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Those gave rise to neural derivatives and those gave rise to cavities.

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So that's what we just talked about.

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That was all from the top part of the neural tube.

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The bottom part of the neural tube, that gives rise to the spinal cord.

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Not really a lot to talk about there.

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Just know that the bottom part of the neural tube becomes the spinal cord.

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Top part of the neural tube basically becomes everything else.

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So I flew through that, but that is nervous system embryology.

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Again, I'd probably re-watch this video once or twice because it is a complex topic, but at the end of the day, if they're going to ask you questions about this,

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they'll either ask you about how neuralation works, they'll ask you about pathology, you know, spina bifida, that sort of thing.

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They'll ask you about the derivatives from the top of the neural tube, or they'll just be really, really nice to you and they'll say, where does the spinal cord come from?

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And that's the bottom of the neural tube.

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Good luck.

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Vocabulaire et conseils d’expression pour cette leçon

Cette leçon d’expression orale de niveau C1 s’appuie sur la vidéo « Embryology of the Nervous System ». Les mots qui reviennent le plus souvent : neural, rise, bifida, spina, ectoderm. Cette vidéo contient 186 phrases et 2553 mots à répéter en shadowing. La partie parlée dure 14:48. Le locuteur parle à un rythme naturel d’environ 173 mots par minute, proche d’une conversation courante. Seuls 77 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.

Vocabulaire clé de cette vidéo

Les 15 mots les plus avancés de la vidéo, avec leur prononciation et leur sens :

Mot	Prononciation	Sens
neural adjectif	/ˈnʊɹəl/	neural
ectoderm nom		ectoderme
fold verbe	/ˈfəʊld/	plier
meninx nom	/ˈmi.nɪŋks/	méninge
spinal adjectif	/spaɪ.nəl/	spinal
protrusion nom	/pɹəˈtɹuːʒən/	protubérance
embryology nom		embryologie
cord nom	/ˈkoɹd/	corde
telencephalon nom	/ˌtɛlənˈsɛfələn/	télencéphale
cerebral adjectif	/səˈɹi.bɹəl/	cérébral
derivative nom	/dɪˈɹɪvətɪv/	dérivé
diencephalon nom	/ˌdaɪ̯.ənˈsɛfəlɑn/	diencéphale
medulla nom	/məˈdulə/	moelle allongée
pathology nom	/pəˈθɒləd͡ʒi/	pathologie
hemisphere nom	/ˈhɛmɪsfɪə/	hémisphère

Les verbes à particule que vous entendrez

Mot	Prononciation	Sens
come out verbe	/ˌkʌm ˈaʊt/	sortir
go down verbe		descendre
go through verbe		traverser
move out verbe		déménager

La grammaire de cette vidéo

Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :

Structure	Dans la vidéo
Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait	is shown · is referred · was derived
Propositions relatives who / which + proposition — une précision sur une personne ou une chose	ectoderm, which is · plate, which is · tube, which was
Present perfect have/has + participe passé — une action passée qui compte encore maintenant	I've just described

Prononciation à surveiller

Le locuteur utilise 36 contractions et formes réduites, comme you're, they'll, I'm. Prononcez-les sous leur forme courte, telles que vous les entendez.

Les sons « th »: pathology /pəˈθɒləd͡ʒi/, thalamus /ˈθæləməs/
Les sons « sh » et « zh »: protrusion /pɹəˈtɹuːʒən/, neuralation /ˌn(j)uːɹəˈleɪʃən/, manifestation /ˌmænɪfɛˈsteɪʃən/, differentiate /dɪf.əˈɹɛn.ʃi.eɪt/
Mots longs — placez bien l’accent: telencephalon /ˌtɛlənˈsɛfələn/, mesencephalon /ˌmɛzənˈsɛfələn/, derivative /dɪˈɹɪvətɪv/, anencephaly /æn.ɪnˈsɛ.fə.lɪ/, diencephalon /ˌdaɪ̯.ənˈsɛfəlɑn/

Les sons difficiles pour les francophones :

/tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: pathology /pəˈθɒləd͡ʒi/, blastula /ˈblæst͡ʃələ/, congenital /kənˈdʒɛnɪt(ə)l/, germ /d͡ʒɝm/, leakage /ˈliːkɪd͡ʒ/
/r/ anglais — langue recourbée, sans frotter la gorge: neural /ˈnʊɹəl/, protrusion /pɹəˈtɹuːʒən/, cord /ˈkoɹd/, ventricle /ˈvɛn.tɹɪk.əl/, cerebral /səˈɹi.bɹəl/

Comment s’entraîner avec cette vidéo

Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme neural, ectoderm, fold.

Qu'est-ce que la technique du Shadowing ?

Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.

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Pratique du Shadowing: Embryology of the Nervous System - Apprendre l'anglais à l'oral avec la vidéo

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