WEBVTT - How Do Sharks' Senses Work?

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<v Speaker 1>Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff

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<v Speaker 1>Lauren Vogelbam here sharks are cool that these beautiful, powerful,

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<v Speaker 1>toothy creatures have been swimming Earth's oceans for some three

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<v Speaker 1>hundred million years. Some species that exist today haven't really

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<v Speaker 1>changed much since the age of the dinosaurs. They fascinate

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<v Speaker 1>and sometimes frighten us because they're such keen predators thanks

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<v Speaker 1>to a number of adaptations that have clearly stood the

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<v Speaker 1>test of time. Though to be clear, we are far

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<v Speaker 1>more of a danger to them than they are to us.

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<v Speaker 1>Toilets injure some forty thousand Americans every year, and sharks

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<v Speaker 1>injure right around fifteen. Not fifteen thousand, just fifteen. But

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<v Speaker 1>it's easy to see why they make us a little

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<v Speaker 1>nervous or perhaps appropriately wary. When we humans swim in

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<v Speaker 1>the ocean, our senses are limited, our hearing is muffled.

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<v Speaker 1>We can't really see without goggles. We can't smell anything

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<v Speaker 1>without breathing in water. But shark senses are perfectly primed

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<v Speaker 1>for an underwater environment. Today, let's talk about how those

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<v Speaker 1>senses work. A firstep smell. The sharks have been referred

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<v Speaker 1>to as swimming noses. A research has shown that some

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<v Speaker 1>sharks can sniff out fish extracts in water at a

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<v Speaker 1>ratio of one part in ten billion. Other research found

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<v Speaker 1>that sharks can respond to as little blood in the

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<v Speaker 1>water as one part in a million. That's like being

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<v Speaker 1>able to detect one teaspoon of something in an Olympic

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<v Speaker 1>sized swimming pool. How does the shark do this? Just

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<v Speaker 1>under the snout are two nasal cavities or neries. Each

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<v Speaker 1>nars has two openings, one for water to enter and

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<v Speaker 1>one for water to exit. The shark sucks or pulls

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<v Speaker 1>the water into the naries through what's called a nasal sack.

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<v Speaker 1>The nasal sack is filled with a series of skin

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<v Speaker 1>folds that contain sensory cells, which send signals to the

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<v Speaker 1>shark's brain. The olfactory lobes and the shark's brain analyze

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<v Speaker 1>the data looking for anything that matches the scent of

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<v Speaker 1>potential prey or potential mates. And sharks have pretty advanced

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<v Speaker 1>equipment up there. The olfactory lobes can make up two

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<v Speaker 1>thirds of a shark's brain weight. Once a shark identifies

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<v Speaker 1>a scent and decides to pursue, it starts swimming the

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<v Speaker 1>shark's natural swimming motion moves its head from side to side,

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<v Speaker 1>which provides further assistance and determining where the scent is

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<v Speaker 1>coming from. Because a shark's sense of smell is directional,

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<v Speaker 1>with each movement the snout picks up more water for

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<v Speaker 1>the shark to analyze and hone in on whatever it's smelling.

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<v Speaker 1>Its sense of smell works so well partially because a

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<v Speaker 1>shark's nose doesn't have anything else to do well. Unlike

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<v Speaker 1>a human with a nose connected to our lungs, sharks

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<v Speaker 1>breed through separate gills. Next up hearing. If you've never

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<v Speaker 1>seen a shark's ear, that's because they have no outer

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<v Speaker 1>ear structures, just a hole on either side of their head.

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<v Speaker 1>But because injured and therefore e prey tend to flop

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<v Speaker 1>around and emit low frequency pulsing hums, it pays for

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<v Speaker 1>sharks to be tuned into those sounds. That pulse is

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<v Speaker 1>sometimes called a yummy hum for that reason, it's like

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<v Speaker 1>a dinner belt to a shark. A shark's ear consists

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<v Speaker 1>of three D shaped, fluid filled canals that allow the

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<v Speaker 1>shark to orient and balance itself like you're inner ears do,

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<v Speaker 1>and tiny hair like structures that sense the vibrations of

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<v Speaker 1>sound waves in the water. Because sound, and especially that

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<v Speaker 1>low frequency sound, travels farther and faster underwater, sharks are

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<v Speaker 1>easily able to detect their prey from distances of more

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<v Speaker 1>than eight hundred feet that's about two hundred and fifty

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<v Speaker 1>meters or more than two football fields. And sharks also

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<v Speaker 1>here with another sensory organ called lateral lines. These are

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<v Speaker 1>a set of tubes that crisscross just under the shark's skin.

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<v Speaker 1>Two main ones run on both sides of the body

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<v Speaker 1>from the shark's head all the way to its tail.

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<v Speaker 1>Water flows into these main tubes through pores on the

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<v Speaker 1>skin in surface. The insides of the tubes are lined

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<v Speaker 1>with more hair like sensory structures. A sound waves or

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<v Speaker 1>nearby movement will cause vibrations in the water in the

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<v Speaker 1>lateral lines, which the shark can interpret to help it

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<v Speaker 1>hone in on things around it. But let's talk vision.

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<v Speaker 1>Some less active sharks that stay near the water's surface

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<v Speaker 1>don't have particularly acute eyesight, while sharks that live in

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<v Speaker 1>the deeps have very large eyes that let them see

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<v Speaker 1>in near darkness. A Most have eyes positioned one on

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<v Speaker 1>each side of their heads, giving them a nearly three

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<v Speaker 1>hundred and sixty degree field of vision. They can typically

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<v Speaker 1>only see about fifty feet or fifteen meters around them,

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<v Speaker 1>and they do have two major blind spots, one right

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<v Speaker 1>in front of the snout and one behind their head,

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<v Speaker 1>so sense of sight is really only important to a

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<v Speaker 1>shark once it's closed in on its prey. Their eyes

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<v Speaker 1>work much like ours, but unlike us, sharks that swim

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<v Speaker 1>in the deep dark parts of the ocean can still

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<v Speaker 1>see well thanks to the tapedum lucidum. This is that's

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<v Speaker 1>the structure located behind the retina that's made of mirror

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<v Speaker 1>like crystals. When light goes through the retina and hits

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<v Speaker 1>those crystals, it's reflected back onto the retina, giving the

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<v Speaker 1>shark a second chance of perceiving anything moving through its

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<v Speaker 1>field of view. A cat's eyes have the same structure,

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<v Speaker 1>and that's why both cat eyes and shark eyes appear

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<v Speaker 1>to glow in the dark, though a shark's to pedem

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<v Speaker 1>lucidum can be about two times as effective as a cat's.

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<v Speaker 1>Humans lack this structure, which is why some sharks can

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<v Speaker 1>see about ten times better than a human can in

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<v Speaker 1>dim light. Another unique thing about shark eyes is the eyelid.

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<v Speaker 1>Sharks use their eyelids primarily as protective measure. When it's

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<v Speaker 1>feeding time or when the shark has an encounter with

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<v Speaker 1>another shark, it will close its eyelids to protect the

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<v Speaker 1>eyes from abrasion. However, a shark's eyelids don't close all

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<v Speaker 1>the way. Some sharks have a third lid, known as

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<v Speaker 1>a nictitating membrane, which will fully protect the eye. Sharks

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<v Speaker 1>that don't have this feature, such as the great white

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<v Speaker 1>and the whale shark, will roll their eyes back into

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<v Speaker 1>their heads to protect the delicate structures. This is also

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<v Speaker 1>why they look wildly wide eyed while they're attacking. Many

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<v Speaker 1>shark species also rely heavily on their sense of taste.

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<v Speaker 1>Before these sharks eat something, they'll give it a test

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<v Speaker 1>bite first. The sensitive taste buds, clustered in the mouth

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<v Speaker 1>analyze the potential meal to see if it's a good one.

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<v Speaker 1>Sharks will often reject prey outside of their ordinary diet,

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<v Speaker 1>such as human beings, after this first bite. And Sharks

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<v Speaker 1>also possess electra reception. They can sense electrical fields elect

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<v Speaker 1>the faint ones created by a beating heart. The organ

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<v Speaker 1>that lets them do this is called the ampullae of Lorenzini.

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<v Speaker 1>These are small clusters of electrically sensitive receptor cells positioned

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<v Speaker 1>under the skin in the shark's head. They're connected to

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<v Speaker 1>pores on the skin's surface via small, jelly filled tubes.

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<v Speaker 1>Researchers are still learning about this organ, but they seem

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<v Speaker 1>to help sharks sense potential prey even if it's not

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<v Speaker 1>flopping about. So yes, all of this makes sharks extremely

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<v Speaker 1>good at what they do and should inspire a healthy

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<v Speaker 1>respect in anything swimming with them. I certainly prefer my

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<v Speaker 1>shark encounters to be from behind some good, thick aquarium glass.

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<v Speaker 1>Today's episode is based on the article how do Sharks

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<v Speaker 1>ce Smellin' Here? On how stuff Works dot Com written

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<v Speaker 1>by Molly Edmonds, with additional material from the article What's

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<v Speaker 1>the Shark's Bummy Hum? By Josh Clark and the brain

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<v Speaker 1>stuff video how do Shark Senses Work? Written by Ben Bollen.

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<v Speaker 1>Brainstuff is production of i Heeart Radio in partnership with

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<v Speaker 1>how stuff Works dot Com, and it's produced by Tyler Klang.

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<v Speaker 1>Four more podcasts my heart Radio, visit the iHeartRadio app,

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<v Speaker 1>Apple Podcasts, or wherever you listen to your favorite shows,