Squeaks, I'm so excited for your big trip!
You're going to see so many new places!
Oh yeah, I wish I could go with you too, but I promised our neighbor that I would take care of her garden while she visits her family, and I don't want to go back on a promise.
I'll miss you too, buddy.
We'll go on another trip together someday.
But I thought of a way that I could still kind of join you this time.
Ta-da!
Tiny Jessie can come with you!
Well, Tiny Jessie can't experience everything exactly like I can.
Humans experience the world through our senses, and Tiny Jessie doesn't have senses.
But maybe she can help remind you of the senses that I use to explore.
For example, you'll be going to see some amazing places.
Exactly, using your eyes.
Eyes are really cool body parts that help animals survive.
An animal's eyes take in information about the world around them, like if there's food or water nearby or something dangerous to avoid.
Animals can do these things using other senses too, but eyes help us by letting our brains understand light.
When I see something like your luggage bag, what's really happening is light is reflecting off of its surface and into my eyes.
The black circle in the middle of my eye is actually a hole called a pupil.
That's where light comes in.
Then the light goes through the lens which focuses all the light into a small point, and then it hits the back of my eye, called the retina.
The retina helps turn the light into special signals that can get carried to my brain through my optic nerves.
And once the signals get there, my brain can make sense of it all, and I see your luggage.
Yeah, senses like sight are complicated.
My eyes have lots of little structures or parts inside, but they're all tools that help my brain to sense light and understand the world.
Squeaks is asking about color, and yes, my eyes help me to understand and sense color, too.
Objects that are different colors reflect slightly different kinds of light, and eyes have to make sense of these differences.
The retinas at the back of my eyes have two different structures for understanding the light that reaches them.
Together, they're called photoreceptors.
Rods are one kind of photoreceptor.
They send my brain signals when there's just a little light to see.
This is important for seeing things when it's dark out, but rods don't tell me anything about color.
It's the other kind of photoreceptor, called cones, that help me see colors.
Most people have three types of cones, and each is better at picking up a different kind of light.
Like, one is really good at picking up blue light, and another is best at picking up red light.
That way, my brain can take the different messages these cones send together and turn them into any color we can see, from orange to light, yellow to dark, green or pink, like your nose.
It's like my brain is mixing light like you or I might mix paints and coming up with one final color that we're actually seeing.
Oh, good question, Squeaks.
Squeaks wants to know if everyone's eyes work this way.
The answer is actually no.
What do I mean?
Well, even among humans, there's a lot of difference in how our eyes work.
Lots of people's eyes see things as blurry unless objects are really close or if objects are really far away.
This is because their eyeballs are shaped a bit differently.
And it causes the light that goes through the lens to focus either in front of or behind the retina instead of right in the retina, where all of those important rods and cones are.
This is why some people wear glasses.
Glasses help to move the light just a little bit, so the light can focus right at the retina in the back of the eyes.
Meanwhile, for some people, their cones don't respond as well to the colors they're supposed to.
Or they might have been born without one or more types of cone.
People with eyes like this see colors differently.
Like they might see shades of red and shades of green as pretty much the same, even though other people like me can see red and green as being very different.
We call conditions like this colorblindness, when people's eyes can't see the full rainbow of light that other people can.
And there are actually lots of animals besides humans that are colorblind or at least can't see the same number of colors that we do.
Fish, dogs, cats, they all see fewer colors than humans.
Meanwhile, some animals can see more colors and kinds of light that we can't see at all.
Can you guess what kind of animal that has special vision?
Birds!
I have an idea.
Let's give Bill and Webb a call.
Hi, Bill.
Hi, Webb.
Hi, Jessie and Squeaks.
Bill and I were just arguing about which color is better, blue, like my hat, Or red, like my scarf.
Maybe you could help settle the debate.
Squeaks and I were just talking about colors.
I think blue is a great color for Webb, and red is a great color for Bill.
Interesting opinion.
I like it.
Me too.
So what's up?
Squeaks and I are learning about eyes and how they work.
And I once heard that birds can see a special type of light.
Oh, I love my eyes.
Birds like us can see colors, like humans do, but we can also see a type of light called ultraviolet light or UV light.
UV light is basically invisible to humans, but birds have an extra kind of cone in our eyes that lets us see it.
It helps us to find food that reflects ultraviolet light.
Oh, and birds can also see certain patterns on each other's feathers that reflect ultraviolet light.
Our eyes see these ultraviolet patches on each other and whether the patches are lighter or darker, so we can tell each other apart by the ultraviolet light from our feathers.
To a human, two birds might look like identical twins, but to us, they look different.
I don't see any ultraviolet spots on you Squeaks, but maybe we can get some UV paint from the craft store and give you some ultraviolet stripes next time we hang out.
That sounds so fun.
Let's get together after Squeaks comes back from his trip.
Bye.
Bye.
So tiny Jessie might not have eyes that work like mine or yours or Bill and Webb's, but I have another present for you that can help me experience all of the cool things you'll see.
It's a camera!
Now you and Tiny Jessie can take pictures of everything you see on your trip.
And when you get home, I can use my eyes to see all of the special places that you visited.
Okay, just one more photo.
Say cheese!
Nice!
Oh, hi there!
Squeaks is going on a trip around the world and because I can't go with him, he's bringing Tiny Jesse to keep him company.
But since Tiny Jesse doesn't have real eyes like I do, he's going to take photos with this camera so I can see all of the cool stuff that he experienced.
Oh, I hadn't thought of that.
Squeaks is wondering how I might be able to hear all of the cool places he's going to visit.
You are going to hear lots of amazing sounds on your trip, like rushing waterfalls or chirping birds or people playing musical instruments.
And just like Tiny Jessie can't see like I can, she also can't hear.
Those tiny ears of hers sure are cute, but they aren't real.
So let's think about how ears work and then use that to find a way that you can help me hear the sounds of your adventure after you get back.
Sounds can help us understand if there's a friend talking to us or popcorn popping or a thunderstorm rumbling.
Our ears are body parts that can help our brains hear and understand sounds.
And once we understand a sound, we can make a decision like go get some of that yummy popcorn or hurry inside before it starts to rain.
That's right.
It's super helpful.
Now, each sound is a special kind of wave that can move through the air or water or even solids like wood.
And it does that by wiggling tiny particles in the air or this table just a little bit.
Can you see the wave moving through it?
When a sound wave reaches my ear, it first runs into the auricle.
That's the big flappy part of the ear that helps collect sound waves and directs them into the auditory canal.
But you have other ear parts that are inside your head, so we're not done yet.
All that wiggling air travels down the auditory canal and starts to wiggle a special part of your ear that looks a bit like the head of a drum.
Exactly, the eardrum.
Although scientists have another name for it too, the tympanic membrane.
No, the eardrum doesn't wiggle my brain.
In fact, everything from the auricle to the eardrum is considered to be part of the outer ear.
But behind the eardrum, there's also the middle ear and the inner ear.
Yeah, there really is a lot more to the ear than you might think.
The middle ear is where the sound waves get amplified, or made stronger.
And in this particular spot you've got three teeny tiny bones that move.
That stronger signal to the inner ear.
The inner ear is the home to the structure called the cochlea.
It's shaped kind of like a snail shell.
And inside of it, there's some liquid and a bunch of teeny tiny hairs.
Uh, no, not like the hairs on my head.
They're really a kind of nerve, which is a cell that can send messages to other parts of your body.
So when the bones from the middle ear bring the sound wave to the cochlea, the hairs start to wiggle too, which finally sends a signal to your brain.
And then your brain can take all that information and go, hey, I heard something.
Ooh, good question!
Squeaks wants to know if I can hear all kinds of vibrations.
I can't hear every kind of sound wave.
If a sound wave is too quiet, it won't get all the parts in my ear wiggling.
But also, it has to be the right pitch.
You can think about pitch as the different notes.
You can play on a keyboard or sing using your voice.
Here's an example of a higher pitch.
And here's an example of a lower pitch.
And depending on my pitch, I can wiggle the air a little bit differently.
But just like musical instruments can only make a certain range of pitches, human ears can only hear sound waves within a certain range of pitches.
If the pitch is too low or too high, We can't hear it no matter how loud it is.
But that's not all.
Because just like every human can't see the exact same colors, we don't all hear the same sounds.
For example, many people lose the ability to hear certain pitches as they get older or if different parts of their ears get damaged.
Also, some people are born unable to hear some or all of the sounds that others can.
People who are deaf or hard of hearing might use technology to help them hear, like a hearing aid to make sounds louder, or a device called a cochlear implant that sends vibrations straight to the nerves and skips over the rest of the ear.
That isn't working so well.
Yeah, there are lots of people who use tools like these, of all ages, too.
Everyone's ears are different.
But that's not just true for humans.
It's also true for other animal species.
Lots of animals can hear sounds that humans normally can't, or can't hear sounds that humans normally can.
Say, let's call someone who I know has some pretty impressive ears.
Hi, Sam.
Oh, hi, Bill.
Hi, Jessie.
Hi, Squeaks.
I'm helping Bill with a project.
I'm making Webb a red hat for his birthday.
He's going to love it whether he wants to or not.
What are you two up to?
Well, Squeaks and I, we're talking about how ears work.
And I know that you have some... Some pretty amazing ears.
Man, I love my ears.
Bats like me tend to have really big auricles to funnel sound waves into our ears.
But most of us also have really big cochlea for how small our bodies are.
And we have extra nerves to help us hear really quiet sounds and really high pitches.
That's right.
Squeaks way higher than Jesse can hear.
It's super helpful because a lot of bats use echolocation to get around.
We make a very high pitched noise with our mouth.
And after the sound wave travels for a bit, it might hit something like a tree or a bug and bounce back to us.
When our ears pick up this bounced back sound wave, we know there's a tree that we don't want to accidentally fly into or there's a tasty bug to eat.
That's super useful, Sam.
And Bill, I was curious about something.
I know that you don't have auricles like Sam and I do, but do you mind if I ask how birds hear?
No problem.
Even though we don't have those flappy bits sticking out of our heads, birds still have an auditory canal and eardrum, a middle ear that makes sound waves stronger and an inner ear with nerves that send information to the brain about those sound waves.
Our ear parts look a little different, but they work a lot like yours.
Whoa, that's so cool.
Thanks.
We've got to finish up here, but we'll come visit soon.
Bye.
Bye.
Wow, different animals have some incredible ways of understanding sound with their ears.
And I think I have an idea.
This camera can take pictures, but it can also record video.
And more importantly, Audio.
You can use it to help you record all of the awesome sound waves you come across on your trip.
And Tiny Jesse might not have real ears, but this will help you to save sounds for me to experience later.
Have fun with Squeaks, Tiny Jesse.
Oh, hi.
Welcome back to the fort.
Squeaks is finally going on his trip around the world tomorrow.
And while I've been helping him pack, we've been talking about our senses and the body parts we use to gather information from the world around us.
While I can't go with him, we've come up with ways that I can experience what he senses during his trip.
He's going to use this camera to take pictures to show me what he saw with his eyes and record audio of the sounds that he used his ears to hear.
How else could you share your experiences?
Well, we need to figure out things to do that can take the place of your senses.
Oh, let's see who's calling.
Maybe they can help us.
It's Bill and Webb.
Hi, Jessie.
We need you to settle another argument for us.
Yes, after Bill told you about how birds hear, we decided to learn more about all the senses we have.
I say there are five senses.
Sight, hearing, touch, taste, and smell.
And I say there are more than five.
Like, what about sense of direction?
You know, the one you never seem to have when it's time to go someplace warmer in the winter.
That's not a real sense.
Quack, quack, quack, quack, quack, quack, quack.
Hang on a second, guys.
Sometimes you'll hear people say, we have the five senses Bill just mentioned.
But there really are more senses than that.
First, sensory organs like our eyes have special parts called receptors.
A receptor captures a specific kind of information from the outside world, then changes it into a signal that goes to the brain.
And once the signal gets to the brain, the brain directs the body what to do to respond.
Right!
When we talked about the eye, we talked about photoreceptors, and how we see.
Photoreceptors take in light, then change the light into a signal.
The brain makes sense of that signal, so we know what we're looking at.
And when we talked about the ear, we covered the receptors called hair cells in the inner ear that change sound waves into signals that our brains use for our sense of hearing.
We also have receptors in our tongue, nose, and skin for our senses of taste, smell, and touch.
So that's five senses!
Well, yes, Bill.
Some of the receptors in our skin, like the ones that help us feel if something is soft or bumpy or hard, sense pressure.
And different receptors in the skin help us to sense temperature.
When we wash our hands before we eat, these receptors sense how warm the water is.
But if the water gets too hot, a completely different kind of receptor senses that we might hurt our skin.
These are pain receptors, and they can cause the body to take action fast.
So we pull our hands out from under the hot water quickly, and the skin doesn't get damaged.
I don't like what those receptors make me feel at all.
Yeah, pain hurts.
It does hurt, but pain receptors are super important because they let us know when something's not right with our bodies, so we can figure out what's going on and hopefully fix it if we need to.
Yeah, what about these other senses?
Well, for example, we have receptors that give us a sense of balance.
If you could see deep inside your ears, you'd see a part that's made of three loops full of liquid.
And inside these loops there are little receptors that can send signals up to the brain that tell it which way your head is facing.
This is how we know which way is up, down, left, and right.
Without this sense, we couldn't stand or sit upright.
I never thought about that before, but that's an important sense.
It would be hard to fly without it.
Yes, there are other senses too.
There's also a really cool one called proprioception.
Whoa, that's a big word.
I think it's a fun length.
Proprioception.
Way more fun to say than sight or hearing, but what's it mean?
Proprioception is the sense of where our body is in space.
Okay, how about this?
Close your eyes and think about where the tips of your wings are, or your fingers if you have them.
Now, touch your bill or nose.
Super easy, right?
Even though you couldn't see anything, while you were moving your body, you knew where everything was.
That's proprioception.
Where are the receptors for proprioception?
Well, they're found in places like your muscles and joints.
This sense of body awareness also helps us figure out how much force we need to use when doing different activities.
Like, picking up an empty water bottle is going to require a little less oomph than a full one.
Speaking of water, what about feeling thirsty?
That's gotta be a sense.
Nah, that's just part of the sense of taste.
No, it's not.
Quack, quack, quack, quack, quack.
Remember, to be a sense, there have to be receptors.
Our tongues have receptors in them that sense different flavors, like salty or sweet.
But there's no thirst receptor.
Instead, we feel thirsty when our brain detects the amount of water throughout our body is getting too low.
Okay, but what about my sense of the passage of time?
Well, that's not a sense at all!
Quack, quack, quack!
Bill!
Webb!
Okay, bye guys.
You want tiny Jessie to experience balance and proprioception for me?
What else are you going to do on your trip, Squeaks?
Dancing?
That sounds amazing!
Dancing requires both balance and muscle movement.
Although, remember, Tiny Jessie doesn't have receptors.
That's why you're bringing the camera.
So, you know what you can do?
You can learn a dance routine from one of the countries you're going to and then come back and teach me.
Then I'll get to experience the movement and balance that you did.
Alright, it's a plan!
And here's the thing, you'll have to use many of your other senses to get that routine to me.
You'll have to watch the dancers, and listen to the sounds they're dancing to, and more.
I can't wait until your back squeaks!
Although, Tiny Jessie will keep you company throughout your journey.
Thanks for joining all of us on SciShow Kids.
If you want to have fun with me, Squeaks, and all our friends, you can subscribe to SciShow Kids.
And we'll see you next time here at the Fort.
