[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.04,0:00:09.66,Default,,0000,0000,0000,,It's the first sense you use\Nwhen you're born.
Dialogue: 0,0:00:09.69,0:00:12.86,Default,,0000,0000,0000,,One out of every fifty of your genes\Nis dedicated to it.
Dialogue: 0,0:00:12.88,0:00:14.58,Default,,0000,0000,0000,,It must be important, right?
Dialogue: 0,0:00:14.61,0:00:17.23,Default,,0000,0000,0000,,Okay, take a deep breath\Nthrough your nose.
Dialogue: 0,0:00:17.25,0:00:18.76,Default,,0000,0000,0000,,It's your sense of smell,
Dialogue: 0,0:00:18.78,0:00:20.68,Default,,0000,0000,0000,,and it's breathtakingly powerful.
Dialogue: 0,0:00:20.70,0:00:24.22,Default,,0000,0000,0000,,As an adult, you can distinguish\Nabout 10,000 different smells.
Dialogue: 0,0:00:24.25,0:00:25.73,Default,,0000,0000,0000,,Here's how your nose does it.
Dialogue: 0,0:00:25.76,0:00:29.12,Default,,0000,0000,0000,,Smell starts when you sniff molecules\Nfrom the air into your nostrils.
Dialogue: 0,0:00:29.14,0:00:30.82,Default,,0000,0000,0000,,95% of your nasal cavity
Dialogue: 0,0:00:30.85,0:00:33.98,Default,,0000,0000,0000,,is used just to filter that air\Nbefore it hits your lungs.
Dialogue: 0,0:00:34.00,0:00:35.58,Default,,0000,0000,0000,,But at the very back of your nose
Dialogue: 0,0:00:35.60,0:00:37.96,Default,,0000,0000,0000,,is a region called\Nthe olfactory epithelium,
Dialogue: 0,0:00:37.98,0:00:40.70,Default,,0000,0000,0000,,a little patch of skin\Nthat's key to everything you smell.
Dialogue: 0,0:00:40.72,0:00:43.92,Default,,0000,0000,0000,,The olfactory epithelium has\Na layer of olfactory receptor cells,
Dialogue: 0,0:00:43.94,0:00:45.84,Default,,0000,0000,0000,,special neurons that sense smells,
Dialogue: 0,0:00:45.86,0:00:47.69,Default,,0000,0000,0000,,like the taste buds of your nose.
Dialogue: 0,0:00:47.71,0:00:49.86,Default,,0000,0000,0000,,When odor molecules hit\Nthe back of your nose,
Dialogue: 0,0:00:49.88,0:00:53.26,Default,,0000,0000,0000,,they get stuck in a layer of mucus\Ncovering the olfactory epithelium.
Dialogue: 0,0:00:53.29,0:00:56.10,Default,,0000,0000,0000,,As they dissolve, they bind\Nto the olfactory receptor cells,
Dialogue: 0,0:00:56.12,0:00:58.76,Default,,0000,0000,0000,,which fire and send signals\Nthrough the olfactory tract
Dialogue: 0,0:00:58.79,0:00:59.92,Default,,0000,0000,0000,,up to your brain.
Dialogue: 0,0:00:59.94,0:01:01.60,Default,,0000,0000,0000,,As a side note, you can tell a lot
Dialogue: 0,0:01:01.62,0:01:03.69,Default,,0000,0000,0000,,about how good\Nan animal's sense of smell is
Dialogue: 0,0:01:03.71,0:01:05.73,Default,,0000,0000,0000,,by the size of its olfactory epithelium.
Dialogue: 0,0:01:05.75,0:01:07.08,Default,,0000,0000,0000,,A dog's olfactory epithelium
Dialogue: 0,0:01:07.11,0:01:09.48,Default,,0000,0000,0000,,is 20 times bigger\Nthan your puny human one.
Dialogue: 0,0:01:09.50,0:01:13.08,Default,,0000,0000,0000,,But there's still a lot we don't know\Nabout this little patch of cells, too.
Dialogue: 0,0:01:13.10,0:01:15.49,Default,,0000,0000,0000,,For example, our olfactory\Nepithelium is pigmented,
Dialogue: 0,0:01:15.52,0:01:17.67,Default,,0000,0000,0000,,and scientists don't really know why.
Dialogue: 0,0:01:17.69,0:01:20.56,Default,,0000,0000,0000,,But how do you actually tell\Nthe difference between smells?
Dialogue: 0,0:01:20.58,0:01:22.10,Default,,0000,0000,0000,,It turns out that your brain has
Dialogue: 0,0:01:22.13,0:01:24.54,Default,,0000,0000,0000,,40 million different\Nolfactory receptor neurons,
Dialogue: 0,0:01:24.56,0:01:27.04,Default,,0000,0000,0000,,so odor A might trigger
Dialogue: 0,0:01:27.06,0:01:29.83,Default,,0000,0000,0000,,neurons 3, 427, and 988,
Dialogue: 0,0:01:29.86,0:01:32.10,Default,,0000,0000,0000,,and odor B might trigger
Dialogue: 0,0:01:32.12,0:01:36.28,Default,,0000,0000,0000,,neurons 8, 76, and 2,496,678.
Dialogue: 0,0:01:36.31,0:01:37.98,Default,,0000,0000,0000,,All of these different combinations
Dialogue: 0,0:01:38.00,0:01:40.44,Default,,0000,0000,0000,,let you detect a staggeringly\Nbroad array of smells.
Dialogue: 0,0:01:40.46,0:01:43.17,Default,,0000,0000,0000,,Olfactory neurons are always fresh\Nand ready for action.
Dialogue: 0,0:01:43.20,0:01:46.27,Default,,0000,0000,0000,,They're the only neuron in the body\Nthat gets replaced regularly,
Dialogue: 0,0:01:46.30,0:01:47.63,Default,,0000,0000,0000,,every four to eight weeks.
Dialogue: 0,0:01:47.65,0:01:50.50,Default,,0000,0000,0000,,Once they are triggered,\Nthe signal travels through a bundle
Dialogue: 0,0:01:50.52,0:01:51.77,Default,,0000,0000,0000,,called the olfactory tract
Dialogue: 0,0:01:51.80,0:01:54.92,Default,,0000,0000,0000,,to destinations all over your brain,\Nmaking stops in the amygdala,
Dialogue: 0,0:01:54.94,0:01:56.49,Default,,0000,0000,0000,,the thalamus, and the neocortex.
Dialogue: 0,0:01:56.51,0:01:59.20,Default,,0000,0000,0000,,This is different from how sight\Nand sound are processed.
Dialogue: 0,0:01:59.22,0:02:01.57,Default,,0000,0000,0000,,Each of those signals goes first\Nto a relay center
Dialogue: 0,0:02:01.59,0:02:03.50,Default,,0000,0000,0000,,in the middle of the cerebral hemisphere
Dialogue: 0,0:02:03.52,0:02:05.54,Default,,0000,0000,0000,,and then out to other\Nregions of the brain.
Dialogue: 0,0:02:05.56,0:02:08.58,Default,,0000,0000,0000,,But smell, because it evolved\Nbefore most of your other senses,
Dialogue: 0,0:02:08.60,0:02:11.49,Default,,0000,0000,0000,,takes a direct route\Nto these different regions of the brain,
Dialogue: 0,0:02:11.51,0:02:13.97,Default,,0000,0000,0000,,where it can trigger\Nyour fight-or-flight response,
Dialogue: 0,0:02:13.100,0:02:16.48,Default,,0000,0000,0000,,help you recall memories,\Nor make your mouth water.
Dialogue: 0,0:02:16.50,0:02:19.41,Default,,0000,0000,0000,,But even though we've all got\Nthe same physiological set-up,
Dialogue: 0,0:02:19.43,0:02:21.63,Default,,0000,0000,0000,,two nostrils and millions\Nof olfactory neurons,
Dialogue: 0,0:02:21.65,0:02:23.43,Default,,0000,0000,0000,,not everybody smells the same things.
Dialogue: 0,0:02:23.46,0:02:25.34,Default,,0000,0000,0000,,One of the most famous examples of this
Dialogue: 0,0:02:25.36,0:02:27.80,Default,,0000,0000,0000,,is the ability to smell\Nso-called "asparagus pee."
Dialogue: 0,0:02:27.83,0:02:29.64,Default,,0000,0000,0000,,For about a quarter of the population,
Dialogue: 0,0:02:29.66,0:02:31.23,Default,,0000,0000,0000,,urinating after eating asparagus
Dialogue: 0,0:02:31.25,0:02:33.08,Default,,0000,0000,0000,,means smelling a distinct odor.
Dialogue: 0,0:02:33.11,0:02:35.58,Default,,0000,0000,0000,,The other 75% of us don't notice.
Dialogue: 0,0:02:35.60,0:02:38.86,Default,,0000,0000,0000,,And this isn't the only case\Nof smells differing from nose to nose.
Dialogue: 0,0:02:38.89,0:02:41.91,Default,,0000,0000,0000,,For some people, the chemical\Nandrostenone smells like vanilla;
Dialogue: 0,0:02:41.93,0:02:44.08,Default,,0000,0000,0000,,to others, it smells like sweaty urine,
Dialogue: 0,0:02:44.11,0:02:45.13,Default,,0000,0000,0000,,which is unfortunate
Dialogue: 0,0:02:45.15,0:02:48.57,Default,,0000,0000,0000,,because androstenone is commonly found\Nin tasty things like pork.
Dialogue: 0,0:02:48.59,0:02:50.72,Default,,0000,0000,0000,,So with the sweaty urine smellers in mind,
Dialogue: 0,0:02:50.74,0:02:52.96,Default,,0000,0000,0000,,pork producers will castrate male pigs
Dialogue: 0,0:02:52.98,0:02:55.02,Default,,0000,0000,0000,,to stop them from making androstenone.
Dialogue: 0,0:02:55.04,0:02:57.79,Default,,0000,0000,0000,,The inability to smell a scent\Nis called anosmia,
Dialogue: 0,0:02:57.82,0:02:59.76,Default,,0000,0000,0000,,and there are about 100 known examples.
Dialogue: 0,0:02:59.78,0:03:03.05,Default,,0000,0000,0000,,People with allicin anosmia\Ncan't smell garlic.
Dialogue: 0,0:03:03.07,0:03:05.92,Default,,0000,0000,0000,,Those with eugenol anosmia\Ncan't smell cloves.
Dialogue: 0,0:03:05.95,0:03:08.52,Default,,0000,0000,0000,,And some people can't smell anything
Dialogue: 0,0:03:08.55,0:03:09.73,Default,,0000,0000,0000,,at all.
Dialogue: 0,0:03:09.75,0:03:12.28,Default,,0000,0000,0000,,This kind of full anosmia\Ncould have several causes.
Dialogue: 0,0:03:12.30,0:03:14.49,Default,,0000,0000,0000,,Some people are born\Nwithout a sense of smell.
Dialogue: 0,0:03:14.52,0:03:17.53,Default,,0000,0000,0000,,Others lose it after an accident\Nor during an illness.
Dialogue: 0,0:03:17.56,0:03:20.07,Default,,0000,0000,0000,,If the olfactory epithelium\Ngets swollen or infected,
Dialogue: 0,0:03:20.09,0:03:21.71,Default,,0000,0000,0000,,it can hamper your sense of smell,
Dialogue: 0,0:03:21.74,0:03:24.45,Default,,0000,0000,0000,,something you might have experienced\Nwhen you were sick.
Dialogue: 0,0:03:24.48,0:03:27.77,Default,,0000,0000,0000,,Not being able to smell anything\Ncan mess with your other senses, too.
Dialogue: 0,0:03:27.80,0:03:29.42,Default,,0000,0000,0000,,Many people who can't smell at all
Dialogue: 0,0:03:29.45,0:03:32.03,Default,,0000,0000,0000,,also can't really taste\Nthe same way the rest of us do.
Dialogue: 0,0:03:32.06,0:03:35.92,Default,,0000,0000,0000,,It turns out that how something tastes\Nis closely related to how it smells.
Dialogue: 0,0:03:35.94,0:03:38.84,Default,,0000,0000,0000,,As you chew your food,\Nair is pushed up your nasal passage,
Dialogue: 0,0:03:38.86,0:03:40.84,Default,,0000,0000,0000,,carrying with it the smell of your food.
Dialogue: 0,0:03:40.87,0:03:42.95,Default,,0000,0000,0000,,Those scents hit your olfactory epithelium
Dialogue: 0,0:03:42.97,0:03:45.36,Default,,0000,0000,0000,,and tell your brain a lot\Nabout what you're eating.
Dialogue: 0,0:03:45.38,0:03:48.16,Default,,0000,0000,0000,,Without the ability to smell,\Nyou lose the ability to taste
Dialogue: 0,0:03:48.18,0:03:50.35,Default,,0000,0000,0000,,anything more complicated\Nthan the five tastes
Dialogue: 0,0:03:50.37,0:03:51.96,Default,,0000,0000,0000,,your taste buds can detect:
Dialogue: 0,0:03:51.99,0:03:53.46,Default,,0000,0000,0000,,sweet, salty,
Dialogue: 0,0:03:53.48,0:03:55.21,Default,,0000,0000,0000,,bitter, sour, and savory.
Dialogue: 0,0:03:55.23,0:03:57.23,Default,,0000,0000,0000,,So, the next time you smell exhaust fumes,
Dialogue: 0,0:03:57.25,0:03:58.95,Default,,0000,0000,0000,,salty sea air, or roast chicken,
Dialogue: 0,0:03:58.97,0:04:00.89,Default,,0000,0000,0000,,you'll know exactly how you've done it
Dialogue: 0,0:04:00.91,0:04:03.92,Default,,0000,0000,0000,,and, perhaps, be a little more\Nthankful that you can.