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How your muscular system works - Emma Bryce

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    Each time you take a step,
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    200 muscles work in unison
    to lift your foot,
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    propel it forward,
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    and set it down.
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    It's just one of the many thousands
    of tasks performed by the muscular system.
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    This network of over 650 muscles
    covers the body
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    and is the reason we can blink,
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    smile,
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    run,
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    jump,
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    and stand upright.
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    It's even responsible for
    the heart's dependable thump.
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    First, what exactly
    is the muscular system?
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    It's made up of three main muscle types:
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    skeletal muscle, which attaches
    via tendons to our bones,
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    cardiac muscle, which is only
    found in the heart,
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    and smooth muscle, which lines
    the blood vessels and certain organs,
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    like the intestine and uterus.
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    All three types are
    made up of muscle cells,
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    also known as fibers,
    bundled tightly together.
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    These bundles receive signals from
    the nervous system
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    that contract the fibers, which in turn
    generates force and motion.
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    This produces almost all
    the movements we make.
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    Some of the only parts of the body
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    whose motions aren't governed
    by the muscular system
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    are sperm cells,
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    the hair-like cilia in our airways,
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    and certain white blood cells.
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    Muscle contraction can be split
    into three main types.
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    The first two, shortening muscle fibers
    and lengthening them,
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    generate opposing forces.
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    So the biceps will shorten
    while the triceps will lengthen or relax,
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    pulling up the arm and making it
    bend at the elbow.
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    This allows us to, say, pick up a book,
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    or if the muscle relationship
    is reversed, put it down.
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    This complimentary partnership
    exists throughout the muscular system.
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    The third type of contraction
    creates a stabilizing force.
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    In these cases, the muscle fibers
    don't change in length,
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    but instead keep the muscles rigid.
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    This allows us to grip a mug of coffee
    or lean against a wall.
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    It also maintains our posture
    by holding us upright.
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    Skeletal muscles form the bulk
    of the muscular system,
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    make up about 30-40% of the body's weight,
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    and generate most of its motion.
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    Some muscles are familiar to us,
    like the pectorals and the biceps,
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    Others may be less so,
    like the buccinator,
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    a muscle that attaches your cheek
    to your teeth,
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    or the body's tiniest skeletal muscle,
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    a one-millimeter-long tissue fragment
    called the stapedius
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    that's nestled deep inside the ear.
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    Wherever they occur, skeletal muscles are
    connected to the somatic nervous system,
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    which gives us almost complete control
    over their movements.
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    This muscle group also contains
    two types of muscle fibers
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    to refine our motions even further,
    slow-twitch and fast-twitch.
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    Fast-twitch fibers react instantly
    when triggered
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    but quickly use up their energy
    and tire out.
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    Slow-twitch fibers, on the other hand,
    are endurance cells.
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    They react and use energy slowly
    so they can work for longer periods.
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    A sprinter will accumulate more
    fast-twitch muscles in her legs
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    through continuous practice,
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    enabling her to quickly, if briefly,
    pick up the pace,
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    whereas back muscles contain
    more slow-twitch muscles
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    to maintain your posture all day.
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    Unlike the skeletal muscles, the body's
    cardiac and smooth muscles
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    are managed by
    the autonomic nervous system
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    beyond our direct control.
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    That makes your heart thumb roughly
    3 billion times
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    over the course of your life,
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    which supplies the body
    with blood and oxygen.
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    Autonomic control also contracts
    and relaxes smooth muscle
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    in a rhythmic cycle.
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    That pumps blood through the smooth
    internal walls of blood vessels,
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    enables the intestine to constrict and
    push food through the digestive system
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    and allows the uterus to contract
    when a person is giving birth.
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    As muscles work, they also use energy
    and produce an important byproduct, heat.
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    In fact, muscle provides
    about 85% of your warmth,
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    which the heart and blood vessels
    then spread evenly across the body
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    via the blood.
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    Without that, we couldn't maintain
    the temperature necessary
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    for our survival.
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    The muscular system
    may be largely invisible to us,
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    but it leaves its mark on almost
    everything we do,
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    whether its the blink of an eye
    or a race to the finish line.
Title:
How your muscular system works - Emma Bryce
Description:

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
04:45

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