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Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff

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Speaker 1: Lauren Vogelbam here sharks are cool that these beautiful, powerful,

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Speaker 1: toothy creatures have been swimming Earth's oceans for some three

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Speaker 1: hundred million years. Some species that exist today haven't really

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Speaker 1: changed much since the age of the dinosaurs. They fascinate

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Speaker 1: and sometimes frighten us because they're such keen predators thanks

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Speaker 1: to a number of adaptations that have clearly stood the

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Speaker 1: test of time. Though to be clear, we are far

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Speaker 1: more of a danger to them than they are to us.

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Speaker 1: Toilets injure some forty thousand Americans every year, and sharks

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Speaker 1: injure right around fifteen. Not fifteen thousand, just fifteen. But

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Speaker 1: it's easy to see why they make us a little

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Speaker 1: nervous or perhaps appropriately wary. When we humans swim in

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Speaker 1: the ocean, our senses are limited, our hearing is muffled.

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Speaker 1: We can't really see without goggles. We can't smell anything

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Speaker 1: without breathing in water. But shark senses are perfectly primed

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

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Speaker 1: senses work. A firstep smell. The sharks have been referred

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Speaker 1: to as swimming noses. A research has shown that some

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Speaker 1: sharks can sniff out fish extracts in water at a

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Speaker 1: ratio of one part in ten billion. Other research found

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Speaker 1: that sharks can respond to as little blood in the

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Speaker 1: water as one part in a million. That's like being

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Speaker 1: able to detect one teaspoon of something in an Olympic

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Speaker 1: sized swimming pool. How does the shark do this? Just

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Speaker 1: under the snout are two nasal cavities or neries. Each

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Speaker 1: nars has two openings, one for water to enter and

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Speaker 1: one for water to exit. The shark sucks or pulls

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Speaker 1: the water into the naries through what's called a nasal sack.

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Speaker 1: The nasal sack is filled with a series of skin

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Speaker 1: folds that contain sensory cells, which send signals to the

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Speaker 1: shark's brain. The olfactory lobes and the shark's brain analyze

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Speaker 1: the data looking for anything that matches the scent of

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Speaker 1: potential prey or potential mates. And sharks have pretty advanced

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Speaker 1: equipment up there. The olfactory lobes can make up two

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Speaker 1: thirds of a shark's brain weight. Once a shark identifies

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Speaker 1: a scent and decides to pursue, it starts swimming the

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Speaker 1: shark's natural swimming motion moves its head from side to side,

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Speaker 1: which provides further assistance and determining where the scent is

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

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Speaker 1: with each movement the snout picks up more water for

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

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Speaker 1: Its sense of smell works so well partially because a

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

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Speaker 1: a human with a nose connected to our lungs, sharks

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Speaker 1: breed through separate gills. Next up hearing. If you've never

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Speaker 1: seen a shark's ear, that's because they have no outer

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Speaker 1: ear structures, just a hole on either side of their head.

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Speaker 1: But because injured and therefore e prey tend to flop

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Speaker 1: around and emit low frequency pulsing hums, it pays for

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Speaker 1: sharks to be tuned into those sounds. That pulse is

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Speaker 1: sometimes called a yummy hum for that reason, it's like

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Speaker 1: a dinner belt to a shark. A shark's ear consists

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Speaker 1: of three D shaped, fluid filled canals that allow the

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

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Speaker 1: and tiny hair like structures that sense the vibrations of

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Speaker 1: sound waves in the water. Because sound, and especially that

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Speaker 1: low frequency sound, travels farther and faster underwater, sharks are

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Speaker 1: easily able to detect their prey from distances of more

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Speaker 1: than eight hundred feet that's about two hundred and fifty

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Speaker 1: meters or more than two football fields. And sharks also

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Speaker 1: here with another sensory organ called lateral lines. These are

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

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Speaker 1: Two main ones run on both sides of the body

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Speaker 1: from the shark's head all the way to its tail.

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Speaker 1: Water flows into these main tubes through pores on the

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Speaker 1: skin in surface. The insides of the tubes are lined

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Speaker 1: with more hair like sensory structures. A sound waves or

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Speaker 1: nearby movement will cause vibrations in the water in the

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Speaker 1: lateral lines, which the shark can interpret to help it

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Speaker 1: hone in on things around it. But let's talk vision.

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Speaker 1: Some less active sharks that stay near the water's surface

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Speaker 1: don't have particularly acute eyesight, while sharks that live in

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Speaker 1: the deeps have very large eyes that let them see

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Speaker 1: in near darkness. A Most have eyes positioned one on

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Speaker 1: each side of their heads, giving them a nearly three

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Speaker 1: hundred and sixty degree field of vision. They can typically

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Speaker 1: only see about fifty feet or fifteen meters around them,

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Speaker 1: and they do have two major blind spots, one right

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Speaker 1: in front of the snout and one behind their head,

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Speaker 1: so sense of sight is really only important to a

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Speaker 1: shark once it's closed in on its prey. Their eyes

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Speaker 1: work much like ours, but unlike us, sharks that swim

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Speaker 1: in the deep dark parts of the ocean can still

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Speaker 1: see well thanks to the tapedum lucidum. This is that's

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Speaker 1: the structure located behind the retina that's made of mirror

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Speaker 1: like crystals. When light goes through the retina and hits

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Speaker 1: those crystals, it's reflected back onto the retina, giving the

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Speaker 1: shark a second chance of perceiving anything moving through its

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

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Speaker 1: and that's why both cat eyes and shark eyes appear

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Speaker 1: to glow in the dark, though a shark's to pedem

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Speaker 1: lucidum can be about two times as effective as a cat's.

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Speaker 1: Humans lack this structure, which is why some sharks can

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Speaker 1: see about ten times better than a human can in

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Speaker 1: dim light. Another unique thing about shark eyes is the eyelid.

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Speaker 1: Sharks use their eyelids primarily as protective measure. When it's

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Speaker 1: feeding time or when the shark has an encounter with

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Speaker 1: another shark, it will close its eyelids to protect the

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

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Speaker 1: the way. Some sharks have a third lid, known as

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Speaker 1: a nictitating membrane, which will fully protect the eye. Sharks

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Speaker 1: that don't have this feature, such as the great white

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Speaker 1: and the whale shark, will roll their eyes back into

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Speaker 1: their heads to protect the delicate structures. This is also

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Speaker 1: why they look wildly wide eyed while they're attacking. Many

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Speaker 1: shark species also rely heavily on their sense of taste.

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Speaker 1: Before these sharks eat something, they'll give it a test

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Speaker 1: bite first. The sensitive taste buds, clustered in the mouth

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

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Speaker 1: Sharks will often reject prey outside of their ordinary diet,

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Speaker 1: such as human beings, after this first bite. And Sharks

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Speaker 1: also possess electra reception. They can sense electrical fields elect

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Speaker 1: the faint ones created by a beating heart. The organ

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Speaker 1: that lets them do this is called the ampullae of Lorenzini.

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Speaker 1: These are small clusters of electrically sensitive receptor cells positioned

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Speaker 1: under the skin in the shark's head. They're connected to

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

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Speaker 1: Researchers are still learning about this organ, but they seem

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Speaker 1: to help sharks sense potential prey even if it's not

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Speaker 1: flopping about. So yes, all of this makes sharks extremely

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Speaker 1: good at what they do and should inspire a healthy

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Speaker 1: respect in anything swimming with them. I certainly prefer my

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Speaker 1: shark encounters to be from behind some good, thick aquarium glass.

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Speaker 1: Today's episode is based on the article how do Sharks

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Speaker 1: ce Smellin' Here? On how stuff Works dot Com written

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Speaker 1: by Molly Edmonds, with additional material from the article What's

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Speaker 1: the Shark's Bummy Hum? By Josh Clark and the brain

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Speaker 1: stuff video how do Shark Senses Work? Written by Ben Bollen.

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Speaker 1: Brainstuff is production of i Heeart Radio in partnership with

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

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Speaker 1: Four more podcasts my heart Radio, visit the iHeartRadio app,

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Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows,