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  • Thanks to Brilliant for supporting this episode of SciShow.

  • Go to to learn how you can take your STEM skills

  • to the next level.

  • [♩INTRO]

  • The feeling of a kicking fetus is perhaps one of the more fun parts

  • of having a baby.

  • And these movements serve a purpose well beyond letting you know

  • that that little thing is in there.

  • Like the pilots in Pacific Rim learning to control their giant robotic Jaegers,

  • these movements are evidence that your tiny incipient human's brain

  • is learning to control its body.

  • When a fetus is in the womb, it's not just sitting around waiting to be born.

  • It's actually working really hard to learn everything it needs to survive

  • in the outside world, including breathing, swallowing, and, of course, moving.

  • There are over six hundred muscles in the human body,

  • which makes for a lot of controls to master.

  • So fetuses need to get an early start,

  • and the womb is the perfect place to get some practice in.

  • The first fetal movements happen around seven weeks after the parent's last period.

  • Which is pretty early!

  • They consist of slow bending movements of the head and trunk,

  • and eventually simple movements of the arms and legs.

  • Things start to change at a postmenstrual age of nine to ten weeks.

  • That's when the fetus starts to move with all the parts of its body,

  • and the directions and speeds of these movements start to vary.

  • These movement patterns are called general movements,

  • and their purpose is to explore all the possible combinations of movements

  • the fetus's tiny body can make.

  • These movements generate proprioceptive sensory signals,

  • that is, sensory information about the position and movement of the body.

  • Every possible general movement has its own set of proprioceptive signals,

  • which helps the brain learn what these movements feel like.

  • So not only is the brain sending out all sorts of commands

  • to the muscles in the body, but the body is teaching the brain

  • the consequences of those commands.

  • The brain is learning what groups of neurons

  • are responsible for what movements.

  • It's essentially the equivalent of learning to control a Jaeger

  • by flailing your arms and seeing what happens.

  • It doesn't end there, though.

  • General movements continue to evolve and change

  • throughout pregnancy and into the first few months after birth.

  • More or less.

  • See, these changes in general movements occur at fairly predictable

  • postmenstrual ages, but are not affected by birth.

  • Infants who are born prematurely tend to follow the same

  • motor development patterns as their counterparts who are still in utero,

  • but are the same postmenstrual age.

  • It seems like the brain still needs about the same amount of time

  • to learn to control the body, regardless of whether or not it is still in the uterus.

  • It's not until several months after birth that these general movements

  • are replaced with goal-directed movements,

  • movements used to accomplish specific goals, like rolling over or reaching.

  • However, there are a few goal-directed movements

  • that have to be learned in the uterus.

  • Sucking and swallowing are vital because they help a newborn eat,

  • and therefore survive.

  • So they have to develop before birth.

  • Fetuses have to learn to breathe, too, which they seem to do via hiccuping.

  • Other than that, infants tend to learn goal-directed movements

  • in a consistent order after birth,

  • starting with eye tracking and head balance,

  • and advancing to rolling over, grasping objects,

  • crawling, sitting, standing, and eventually walking.

  • Turns out it's hard work learning to pilot a human body.

  • Thanks for watching this episode of SciShow!

  • If you want to keep learning,

  • why not make a goal-directed movement over to Brilliant?

  • Brilliant is a problem solving-based website and app with a hands-on approach,

  • with over 60 interactive courses in math, science, and computer science.

  • And if we've got you thinking right now,

  • You know, I really do want to learn how to pilot a giant robot,”

  • they might be a good place to start.

  • Like their course on algorithm fundamentals,

  • which is all about getting computers to do what you want.

  • Sound close?

  • Right now, the first 200 people to sign up at

  • will get 20% off the annual Premium subscription.

  • So go forth and design your Jaegers!

  • [♩OUTRO]

Thanks to Brilliant for supporting this episode of SciShow.


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B1 中級

胎兒為什麼會踢得那麼厲害? (Why Do Fetuses Kick So Much?)

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    林宜悉 發佈於 2021 年 01 月 14 日