I’ve got a little challenge for you this week. If you’re able to, stand on one foot
with your hands on your hips for 30 seconds. Keep your feet and hands as still as possible.
If your hands lift off your hips, you lose a point. If your toes come off the ground,
you lose a point. If that’s too easy, close your eyes. That should've made it harder,
but not impossible. With your eyes still closed, put your hands
hands over your ears. That should've made it harder, but why?
Yes, you changed your balance point to be more top heavy, but you also changed
one of your primary ways of establishing balance — your ears. While balancing on one foot
makes for a fun little challenge, this phenomenon also explains the sensation of vertigo. So
in this video, we’ll go over the delicate anatomy that gives us our sense of balance.
To understand how our ears influence balance, we’ll need some background anatomy. Anatomists
typically divide the ear into three main sections: the outer, middle, and inner ear. The outer
ear includes everything you see on the surface plus the ear canal — mostly elastic cartilage
wrapped in skin that’s rich with sebaceous oil glands and ear wax glands. At this point,
the purpose of the ear is just to collect sound waves, kind of like how a satellite
dish is concave to collect radio waves. Those sound waves rattle the eardrum, or tympanic
membrane, an extremely thin membrane that amplifies and transmits sound waves to the
three smallest bones in our bodies — the hammer, anvil, and stirrup or malleus, incus,
and stapes if you want to use Latin. Then those vibrations wiggle the cochlea in the
inner ear, which transforms vibrations into nervous impulses that travel to the brain
and get interpreted as your favorite Tiktok song. This is my how do you do, fellow kids
moment isn’t it? Right next to the cochlea is the tiny vestibular system, which includes
three semicircular canals, and tiny segments called the utricle and saccule, all of which
are filled with fluid. These things are the main organs for balance. If we shrunk down
into the semicircular canals, we’d find a space lined with little sensory cells called
hair cells, named so because they poke out of the canal a little bit — not because
they’re actual hair. Whenever we turn or tilt our heads, the inner ear moves with it,
and the fluid inside the canals sloshes back and forth. And that movement of the fluid
pushes on the hair cells, which are sensitive enough to detect less than a nanometer’s
length worth of movement. Each of those canals detects motion on a different axis — one
detects tilting up or down, one detects rotation, and one detects bending left or right. The
other organs, the utricle and saccule, works similarly. They both have those hair cells,
but they have tiny calcium crystals on them. That makes this part of the balance organ
specialized to detect acceleration. I personally picture the balance organs like those spirit
levels with the bubbles inside them. But instead of our eyes determining the position of the
bubble visually, the sensors are built into the level. From there, the balance organs
work like any other sense. They convert the motion from the hair cells into nervous impulses
and send them to the brain. There, they combine with information like what your eyes are focusing
on, or the position of your foot, or the stretch of certain tendons. But every now
and then, those different inputs conflict with each other like when you’re on a boat
or airplane, which manifests as dizziness or even nausea. Unfortunately, all of these
sensory systems break down as you get older. So it’s no surprise that the elderly are
at a drastically increased risk of experiencing dizziness and falls over their younger selves.
While just about every part of your balance organs deteriorates over time, you start losing
hair cells as you age which contributes to impaired balance. But even before you start
aging, if you have a disease or injury that affects the inner ear, there’s a good chance
it’ll throw off your balance. The most common cause of vertigo in adults is called benign
paroxysmal positional vertigo, or BPPV, and it happens when some of the crystals in the
inner ear become dislodged from where they usually are. Or there’s Meniere’s disease
which is an inner ear disorder that might be caused by abnormal buildup of fluid in
the balance organs — scientists aren’t totally sure why it happens. This causes vertigo
and ringing in the ears, although typically just one ear. So it’s a bit of a tradeoff.
We have this intricate, three dimensional system for detecting our position in space,
but it’s delicate. I wish I could give you hope, or tell you the one secret doctors don’t
want you to know, but it’s a fact of life. You get old, systems break down, then you
die. Well… Thanks for watching Human. Speaking of things coming to an end, this episode marks
the end of season 2 of Human. Don’t worry, we’re still working on videos behind the
scenes, so make sure to subscribe to us here on Youtube and drop a comment if you have
a topic you want me to cover in Season 3. Thanks for watching.