[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.86,0:00:09.41,Default,,0000,0000,0000,,It's the first sense you use when you're born.
Dialogue: 0,0:00:09.41,0:00:11.28,Default,,0000,0000,0000,,One out of every fifty of your genes
Dialogue: 0,0:00:11.28,0:00:12.62,Default,,0000,0000,0000,,is dedicated to it.
Dialogue: 0,0:00:12.62,0:00:14.61,Default,,0000,0000,0000,,It must be important, right?
Dialogue: 0,0:00:14.61,0:00:16.21,Default,,0000,0000,0000,,Okay, take a deep breath
Dialogue: 0,0:00:16.21,0:00:17.25,Default,,0000,0000,0000,,through your nose.
Dialogue: 0,0:00:17.25,0:00:18.43,Default,,0000,0000,0000,,It's your sense of smell,
Dialogue: 0,0:00:18.43,0:00:20.70,Default,,0000,0000,0000,,and it's breathtakingly powerful.
Dialogue: 0,0:00:20.70,0:00:21.88,Default,,0000,0000,0000,,As an adult, you can distinguish
Dialogue: 0,0:00:21.88,0:00:23.96,Default,,0000,0000,0000,,about 10,000 different smells.
Dialogue: 0,0:00:23.96,0:00:25.76,Default,,0000,0000,0000,,Here's how your nose does it.
Dialogue: 0,0:00:25.76,0:00:27.10,Default,,0000,0000,0000,,Smell starts when you sniff molecules
Dialogue: 0,0:00:27.10,0:00:29.07,Default,,0000,0000,0000,,from the air into your nostrils.
Dialogue: 0,0:00:29.07,0:00:30.85,Default,,0000,0000,0000,,95% of your nasal cavitity
Dialogue: 0,0:00:30.85,0:00:32.51,Default,,0000,0000,0000,,is used just to filter that air
Dialogue: 0,0:00:32.51,0:00:34.00,Default,,0000,0000,0000,,before it hits your lungs.
Dialogue: 0,0:00:34.00,0:00:35.18,Default,,0000,0000,0000,,But at the very back of your nose
Dialogue: 0,0:00:35.18,0:00:37.82,Default,,0000,0000,0000,,is a region called the olfactory epithelium,
Dialogue: 0,0:00:37.82,0:00:39.04,Default,,0000,0000,0000,,a little patch of skin
Dialogue: 0,0:00:39.04,0:00:40.54,Default,,0000,0000,0000,,that's key to everything you smell.
Dialogue: 0,0:00:40.54,0:00:42.27,Default,,0000,0000,0000,,The olfactory epithelium has a layer
Dialogue: 0,0:00:42.27,0:00:43.94,Default,,0000,0000,0000,,of olfactory receptor cells,
Dialogue: 0,0:00:43.94,0:00:45.86,Default,,0000,0000,0000,,special neurons that sense smells,
Dialogue: 0,0:00:45.86,0:00:47.71,Default,,0000,0000,0000,,like the taste buds of your nose.
Dialogue: 0,0:00:47.71,0:00:49.66,Default,,0000,0000,0000,,When odor molecules hit the back of your nose,
Dialogue: 0,0:00:49.66,0:00:51.25,Default,,0000,0000,0000,,they get stuck in a layer of mucus
Dialogue: 0,0:00:51.25,0:00:53.29,Default,,0000,0000,0000,,covering the olfactory epithelium.
Dialogue: 0,0:00:53.29,0:00:54.13,Default,,0000,0000,0000,,As they dissolve,
Dialogue: 0,0:00:54.13,0:00:55.96,Default,,0000,0000,0000,,they bind to the olfactory receptor cells,
Dialogue: 0,0:00:55.96,0:00:57.17,Default,,0000,0000,0000,,which fire and send signals
Dialogue: 0,0:00:57.17,0:00:58.62,Default,,0000,0000,0000,,through the olfactory tract
Dialogue: 0,0:00:58.62,0:00:59.94,Default,,0000,0000,0000,,up to your brain.
Dialogue: 0,0:00:59.94,0:01:00.76,Default,,0000,0000,0000,,As a side note,
Dialogue: 0,0:01:00.76,0:01:01.58,Default,,0000,0000,0000,,you can tell a lot
Dialogue: 0,0:01:01.58,0:01:03.33,Default,,0000,0000,0000,,about how good an animal's sense of smell is
Dialogue: 0,0:01:03.33,0:01:05.40,Default,,0000,0000,0000,,by the size of its olfactory epithelium.
Dialogue: 0,0:01:05.40,0:01:06.72,Default,,0000,0000,0000,,A dog's olfactory epithelium
Dialogue: 0,0:01:06.72,0:01:07.88,Default,,0000,0000,0000,,is 20 times bigger
Dialogue: 0,0:01:07.88,0:01:09.50,Default,,0000,0000,0000,,than your puny human one.
Dialogue: 0,0:01:09.50,0:01:10.72,Default,,0000,0000,0000,,But there's still a lot we don't know
Dialogue: 0,0:01:10.72,0:01:12.39,Default,,0000,0000,0000,,about this little patch of cells, too.
Dialogue: 0,0:01:12.39,0:01:15.08,Default,,0000,0000,0000,,For example, our olfactory epithelium is pigmented,
Dialogue: 0,0:01:15.08,0:01:17.69,Default,,0000,0000,0000,,and scientists don't really know why.
Dialogue: 0,0:01:17.69,0:01:18.91,Default,,0000,0000,0000,,But how do you actually tell the difference
Dialogue: 0,0:01:18.91,0:01:20.44,Default,,0000,0000,0000,,between smells?
Dialogue: 0,0:01:20.44,0:01:21.56,Default,,0000,0000,0000,,It turns out that your brain has
Dialogue: 0,0:01:21.56,0:01:24.56,Default,,0000,0000,0000,,40 million different olfactory receptor neurons,
Dialogue: 0,0:01:24.56,0:01:29.86,Default,,0000,0000,0000,,so odor A might trigger neurons 3, 427, and 988,
Dialogue: 0,0:01:29.86,0:01:36.31,Default,,0000,0000,0000,,and odor B might trigger neurons 8, 76, and 2,496,678.
Dialogue: 0,0:01:36.31,0:01:37.49,Default,,0000,0000,0000,,All of these different combinations
Dialogue: 0,0:01:37.49,0:01:40.46,Default,,0000,0000,0000,,let you detect a staggeringly broad array of smells.
Dialogue: 0,0:01:40.46,0:01:42.30,Default,,0000,0000,0000,,Plus, your olfactory neurons are always fresh
Dialogue: 0,0:01:42.30,0:01:43.50,Default,,0000,0000,0000,,and ready for action.
Dialogue: 0,0:01:43.50,0:01:44.67,Default,,0000,0000,0000,,They're the only neuron in the body
Dialogue: 0,0:01:44.67,0:01:46.30,Default,,0000,0000,0000,,that gets replaced regularly,
Dialogue: 0,0:01:46.30,0:01:47.55,Default,,0000,0000,0000,,every four to eight weeks.
Dialogue: 0,0:01:47.55,0:01:48.76,Default,,0000,0000,0000,,Once those neurons are triggered,
Dialogue: 0,0:01:48.76,0:01:49.92,Default,,0000,0000,0000,,the signal travels through a bundle
Dialogue: 0,0:01:49.92,0:01:51.33,Default,,0000,0000,0000,,called the olfactory tract
Dialogue: 0,0:01:51.33,0:01:53.25,Default,,0000,0000,0000,,to destinations all over your brain,
Dialogue: 0,0:01:53.25,0:01:54.25,Default,,0000,0000,0000,,making stops in the amygdala,
Dialogue: 0,0:01:54.25,0:01:54.84,Default,,0000,0000,0000,,the thalamus,
Dialogue: 0,0:01:54.84,0:01:56.09,Default,,0000,0000,0000,,and the neocortex.
Dialogue: 0,0:01:56.09,0:01:56.85,Default,,0000,0000,0000,,This is different
Dialogue: 0,0:01:56.85,0:01:58.40,Default,,0000,0000,0000,,from how sight and sound are processed.
Dialogue: 0,0:01:58.40,0:02:00.06,Default,,0000,0000,0000,,Each of those signals goes first
Dialogue: 0,0:02:00.06,0:02:00.85,Default,,0000,0000,0000,,to a relay center
Dialogue: 0,0:02:00.85,0:02:02.64,Default,,0000,0000,0000,,in the middle of the cerebral hemisphere
Dialogue: 0,0:02:02.64,0:02:05.09,Default,,0000,0000,0000,,and then out to other regions of the brain.
Dialogue: 0,0:02:05.09,0:02:06.62,Default,,0000,0000,0000,,But smell, because it evolved
Dialogue: 0,0:02:06.62,0:02:08.36,Default,,0000,0000,0000,,before most of your other senses,
Dialogue: 0,0:02:08.36,0:02:09.37,Default,,0000,0000,0000,,takes a direct route
Dialogue: 0,0:02:09.37,0:02:11.03,Default,,0000,0000,0000,,to these different regions of the brain,
Dialogue: 0,0:02:11.03,0:02:12.74,Default,,0000,0000,0000,,where it can trigger your fight-or-flight response,
Dialogue: 0,0:02:12.74,0:02:13.98,Default,,0000,0000,0000,,help you recall memories,
Dialogue: 0,0:02:13.98,0:02:15.80,Default,,0000,0000,0000,,or make your mouth water.
Dialogue: 0,0:02:15.80,0:02:16.94,Default,,0000,0000,0000,,But even though we've all got
Dialogue: 0,0:02:16.94,0:02:18.37,Default,,0000,0000,0000,,the same physiological set-up,
Dialogue: 0,0:02:18.37,0:02:20.41,Default,,0000,0000,0000,,two nostrils and millions of olfactory neurons,
Dialogue: 0,0:02:20.41,0:02:23.14,Default,,0000,0000,0000,,not everybody smells the same things.
Dialogue: 0,0:02:23.14,0:02:24.98,Default,,0000,0000,0000,,One of the most famous examples of this
Dialogue: 0,0:02:24.98,0:02:27.83,Default,,0000,0000,0000,,is the ability to smell so-called "asparagus pee."
Dialogue: 0,0:02:27.83,0:02:29.48,Default,,0000,0000,0000,,For about a quarter of the population,
Dialogue: 0,0:02:29.48,0:02:31.25,Default,,0000,0000,0000,,urinating after eating asparagus
Dialogue: 0,0:02:31.25,0:02:33.11,Default,,0000,0000,0000,,means smelling a distinct odor.
Dialogue: 0,0:02:33.11,0:02:35.60,Default,,0000,0000,0000,,The other 75% of us don't notice.
Dialogue: 0,0:02:35.60,0:02:36.65,Default,,0000,0000,0000,,And this isn't the only case
Dialogue: 0,0:02:36.65,0:02:38.77,Default,,0000,0000,0000,,of smells differing from nose to nose.
Dialogue: 0,0:02:38.77,0:02:39.59,Default,,0000,0000,0000,,For some people,
Dialogue: 0,0:02:39.59,0:02:41.93,Default,,0000,0000,0000,,the chemical androstenone smells like vanilla;
Dialogue: 0,0:02:41.93,0:02:44.11,Default,,0000,0000,0000,,to others, it smells like sweaty urine,
Dialogue: 0,0:02:44.11,0:02:45.15,Default,,0000,0000,0000,,which is unfortunate
Dialogue: 0,0:02:45.15,0:02:46.84,Default,,0000,0000,0000,,because androstenone is commonly found
Dialogue: 0,0:02:46.84,0:02:48.59,Default,,0000,0000,0000,,in tasty things like pork.
Dialogue: 0,0:02:48.59,0:02:50.74,Default,,0000,0000,0000,,So with the sweaty urine smellers in mind,
Dialogue: 0,0:02:50.74,0:02:52.98,Default,,0000,0000,0000,,pork producers will castrate male pigs
Dialogue: 0,0:02:52.98,0:02:55.04,Default,,0000,0000,0000,,to stop them from making androstenone.
Dialogue: 0,0:02:55.04,0:02:56.63,Default,,0000,0000,0000,,The inability to smell a scent
Dialogue: 0,0:02:56.63,0:02:57.82,Default,,0000,0000,0000,,is called anosmia,
Dialogue: 0,0:02:57.82,0:02:59.78,Default,,0000,0000,0000,,and there are about 100 known examples.
Dialogue: 0,0:02:59.78,0:03:02.72,Default,,0000,0000,0000,,People with allicin anosmia can't smell garlic.
Dialogue: 0,0:03:02.72,0:03:05.54,Default,,0000,0000,0000,,Those with eugenol anosmia can't smell cloves.
Dialogue: 0,0:03:05.54,0:03:08.55,Default,,0000,0000,0000,,And some people can't smell anything
Dialogue: 0,0:03:08.55,0:03:09.75,Default,,0000,0000,0000,,at all.
Dialogue: 0,0:03:09.75,0:03:10.89,Default,,0000,0000,0000,,This kind of full anosmia
Dialogue: 0,0:03:10.89,0:03:12.30,Default,,0000,0000,0000,,could have several causes.
Dialogue: 0,0:03:12.30,0:03:14.18,Default,,0000,0000,0000,,Some people are born without a sense of smell.
Dialogue: 0,0:03:14.18,0:03:16.21,Default,,0000,0000,0000,,Others lose it after an accident
Dialogue: 0,0:03:16.21,0:03:17.56,Default,,0000,0000,0000,,or during an illness.
Dialogue: 0,0:03:17.56,0:03:20.09,Default,,0000,0000,0000,,If the olfactory epithelium gets swollen or infected,
Dialogue: 0,0:03:20.09,0:03:21.39,Default,,0000,0000,0000,,it can hamper your sense of smell,
Dialogue: 0,0:03:21.39,0:03:22.68,Default,,0000,0000,0000,,something you might have experienced
Dialogue: 0,0:03:22.68,0:03:24.53,Default,,0000,0000,0000,,when you were sick.
Dialogue: 0,0:03:24.53,0:03:25.55,Default,,0000,0000,0000,,And not being able to smell anything
Dialogue: 0,0:03:25.55,0:03:27.48,Default,,0000,0000,0000,,can mess with your other senses, too.
Dialogue: 0,0:03:27.48,0:03:29.31,Default,,0000,0000,0000,,Many people who can't smell at all
Dialogue: 0,0:03:29.31,0:03:31.02,Default,,0000,0000,0000,,also can't really taste the same way
Dialogue: 0,0:03:31.02,0:03:32.06,Default,,0000,0000,0000,,the rest of us do.
Dialogue: 0,0:03:32.06,0:03:33.69,Default,,0000,0000,0000,,It turns out that how something tastes
Dialogue: 0,0:03:33.69,0:03:35.94,Default,,0000,0000,0000,,is closely related to how it smells.
Dialogue: 0,0:03:35.94,0:03:36.90,Default,,0000,0000,0000,,As you chew your food,
Dialogue: 0,0:03:36.90,0:03:38.86,Default,,0000,0000,0000,,air is pushed up your nasal passage,
Dialogue: 0,0:03:38.86,0:03:40.87,Default,,0000,0000,0000,,carrying with it the smell of your food.
Dialogue: 0,0:03:40.87,0:03:42.61,Default,,0000,0000,0000,,Those scents hit your olfactory epithelium
Dialogue: 0,0:03:42.61,0:03:43.92,Default,,0000,0000,0000,,and tell your brain a lot
Dialogue: 0,0:03:43.92,0:03:45.16,Default,,0000,0000,0000,,about what you're eating.
Dialogue: 0,0:03:45.16,0:03:46.70,Default,,0000,0000,0000,,Without the ability to smell,
Dialogue: 0,0:03:46.70,0:03:48.30,Default,,0000,0000,0000,,you lose the ability to taste
Dialogue: 0,0:03:48.30,0:03:49.36,Default,,0000,0000,0000,,anything more complicated
Dialogue: 0,0:03:49.36,0:03:50.37,Default,,0000,0000,0000,,than the five tastes
Dialogue: 0,0:03:50.37,0:03:51.79,Default,,0000,0000,0000,,your taste buds can detect:
Dialogue: 0,0:03:51.79,0:03:52.34,Default,,0000,0000,0000,,sweet,
Dialogue: 0,0:03:52.34,0:03:53.94,Default,,0000,0000,0000,,salty,
Dialogue: 0,0:03:53.94,0:03:53.88,Default,,0000,0000,0000,,bitter,
Dialogue: 0,0:03:53.88,0:03:54.46,Default,,0000,0000,0000,,sour,
Dialogue: 0,0:03:54.46,0:03:55.23,Default,,0000,0000,0000,,and savory.
Dialogue: 0,0:03:55.23,0:03:56.92,Default,,0000,0000,0000,,So, the next time you smell exhaust fumes,
Dialogue: 0,0:03:56.92,0:03:57.93,Default,,0000,0000,0000,,salty sea air,
Dialogue: 0,0:03:57.93,0:03:58.97,Default,,0000,0000,0000,,or roast chicken,
Dialogue: 0,0:03:58.97,0:04:00.91,Default,,0000,0000,0000,,you'll know exactly how you've done it
Dialogue: 0,0:04:00.91,0:04:04.06,Default,,0000,0000,0000,,and, perhaps, be a little more thankful that you can.