Hi. It's Mr. Andersen and in this podcast I'm going to talk about the sensory
system. The sensory system is basically how you sense information in your surroundings
and then transfer that to your brain. And you're using a number of sense right now.
You hear me and you can see me and you can't smell me, but you might be able to smell something
around you. And so basically the cool thing about it is what goes to you're brain are
simply nerve signals. Or we call those action potentials. But what you're brain does with
it is way more complex with that. I can't even get into that today. And what do I mean
by that? Well right here we've got this cylinder and A and B. And A and B, this is just an
optical illusion are exactly the came color. In other words they're the same hue of grey.
And you might say no way. If I were to remove the rest of the drawing, then you see that
they're the same color of grey. And so even though when they were together let's move
it back again, even though they're the same color of grey, and your eye is receiving that
color of grey, your brain is making sense of it. And it's doing that because it realizes
this is maybe in a shadow. And so even though the sensory system brings action potentials
to your brain, know this. That you're brain can do a lot with it when it eventually gets
there. And so review a little bit of the nervous system. Basically nerve signals are action
potentials. So basically all the nerves are sitting at negative 70 millivolts. Anything
that pushes it towards that can cause an action potential. Action potential goes up. We have
an undershoot and it eventually goes back to negative 70. Now what's causing that is
going to be sodium and ions, sodium and potassium ion flow. But basically what it looks like
to the brain is an action potential. And another action potential. And another action potential.
And another action potential. And all the action potentials are identical in size and
identical in shape. But your brain is receiving those and it can tell what the signal is based
on where the signal is coming from, what nerves it's coming from. And basically the number
of action potentials you get. And so if I were to make a noise like hooooooooooooo,
then you would be getting actions potentials from your ear hooooooooooooo. And a set number
of action potentials because it's not really loud. And it's a specific pitch. If I were
to make a slightly louder noise Yawwwwww like that, then that's going to be way more action
potentials. The first sound we could think of as like this. But the second one, it's
going to be way more action potentials. They're always the same size, but more action potentials
in a given period of time. And so again, the action potentials form your nose and the action
potentials from your eyes and your ears and all of those are exactly the same. They look
exactly the same. You either have more of them or less of them. And so you might think
to yourself, well how many senses do you have? Most people would say 5. We have 5 senses
and then we have a 6th sense, which is not something that I'm even going to talk about.
But basically that would be way underestimating the number of senses. Because you can see,
you can hear, you can taste, you can smell, you can touch. But you also have sense of
balance. You make sure that you are remaining upright. You can sense temperature. You can
sense pain. You can sense acceleration. You have kinesthetic sense. I mean take your finger.
Close your eyes. Can you get your finger to your nose? Yeah? How are you doing that? Well
that's kinesthetics. And then you have dozens of other senses inside our body. Internal
senses. And so if somebody says, we've got five senses, I know I'm being picky here,
but we have way more. We have about 25 senses. So, today, what am I going to talk about?
Well I just want to talk about three of those. I'm going to start with the smell. Smell is
not super important in us, but it is important. But just as an example for the next two which
are going to be vision and then hearing. And so basically how does smell work? Well this
is your nose right here. So you have this olfactory bulb which is right up at the top.
So we've kind of zoomed into it here. And so if you want to smell something, how does
that work? Well if you really want to smell a rose, then you kind of sniff. Because you
want to bring those chemicals up into your nose. Because this is a chemical sensor. Just
like your taste buds are sensing chemicals that end up on your taste buds, your sense
of smell is the same way. So the more of those you can get up to this point, the better our
sense of smell is. And a dog is going to have way more receptors than we do. But basically
what happens is those odors are eventually going to dock with these olfactory neurons
right here in your nose. And every time they interact they're going to cause interactions.
And so the more interactions there are, the more action potentials are going to be sent
to your brain. And your brain is going to sense that. And they're going to be able to
tell you what that smell is. Or more of that smell. Now if you've ever walked into somebody's
house you'll notice that their house smells different than your house. They have a smelly
house. But then the longer you are there, eventually you are going to ignore that. And
so even though those smells are present, our brain can decide what we want to do with that
as well. But what's going to your brain again? It's just action potentials that are being
sent down the neurons that go into your brain. And if those action potentials aren't present
then you're not going to be able to smell it. But you're sensing a chemical smell. Let's
go to the next one which is vision. How does vision work? Well vision basically you have
a pupil up here. You have an opening. We have a lens that we can change the focus of. But
let's see, if I were to draw something out here. Let's say you're looking at a person
that's far away. Basically that light is going to be bent, so it's going to be bent like
that. And it's going to be projected on the back of your eye. And so again if it's a,
that's a really bad drawing, but basically we can regulate the amount of light that gets
in but this ends up on the back of our eye. We are then going to transfer that into action
potentials that go to your brain. So you're brain is going to flip that image right side
up. But how does that work? How do we sense that on the back of our eye? Well basically
on the back of our eye, you learn this as a kid, we have rods and cones. And so rods
and cones are going to be found here. Cones will be closer to the middle because cones
are good and sensing, we have what are called this foveae where there's this area where
we have lots of cones. We can sense lots of color. And then as we move farther out we're
going to have rods which are going to sense low light conditions. But they're going to
be in black and white. But what do these receptors look like? Well this is one right here. This
would be a rod right here. A rod is going to pick up light. So basically down here it's
just like a neuron. But we've got a sensory portion to it. You can see that there's synapse
here and then thats' going to send that to cells that are going to go through the optic
nerve and eventually to the brain. If we zoom in right here to this area, we get a lipid
bilayer. And then we have a chemical called rhodopsin. Rhodopsin is going to pick up light.
And so when light hits that. So when light hits rhodopsin, what's going to happen? It's
going to have a conformational change in the protein. The protein will actually change
shape. The rhodopsin is going to change its conformation. When it changes its shape, that's
going to send an action potential down here. It's going to send an action potential down
a nerve and it's going to eventually go to your brain. And so when you see light, so
if we see light here, more light on this side of the retina, that means that more of the
rhodopsin is changing its shape and we're sending more of a signal. Likewise if we see
a dark area or even if we were to close our eyes, we're going to have all that rhodopsin
go back to a specific conformation. We're not going to send action potentials to the
brain. You've noticed this sometimes. You're in a theater. It's really really dark. You
forget that you're in a theater during the day. You go outside, Bam, and you get that
light. Well that's basically all of the rhodopsin in all the rods that are being bleached we
call that. They're sending a bunch of action potentials right to your brain. And so that's
the way vision works. And vision is super important in us and so we have tons and tons
of receptors. Tons and tons of these neurons that are going to send information back to
the brain. Because we're visual kind of people. Hearing is another one. Hearing is not using
electromagnetic radiation. Hearing is actually using compressional sound waves that are passed
in through the air. And so basically when I talk right now I'm vibrating the air. And
that vibrated air is moving into your ear. It's going to vibrate this. This is called
your ear drum. We have a series of bones which are going to mechanically amplify that. Until
it eventually gets right here. And this is going to be your oval window. So the oval
window sits right here on your cochlea. The cochlea looks kind of like a snail. And that's
where you sense hearing. On top of that we have these semi circular canals. Those are
actually going to give you a sense of balance. And so there's fluid inside here. And they've
got three different dimensions. And so basically you can sense movement through three dimensional
space. But how do we sense sound? Well, what I'm, this is an awful drawing here, but basically
if I were to take the cochlea and unwind it, what you get is this long tube. And so basically
the fluid in here is going to vibrate. There are going to be nerves that go out of here
to the auditory nerve. They're going, so again I've unwound the cochlea. So basically what
happens is you're going to vibrate the fluid inside the cochlea. And depending on the pitch,
you're going to vibrate it in a different area. Example, a whale's cochlea is going
to be really, really big. And so it's going to be able to sense really low frequency sounds
that we couldn't even pick up. Or if we had something like a dog that can hear high frequency
sounds, it just means that their cochlea is going to have more neurons. It's going to
have a smaller area in there. Because when we vibrate the sound we're going to vibrate
a specific portion of that cochlea and that's going to send a signal down to our brain.
Again we're going to sense it. It's just going to be action potentials coming to the brain.
But since it's going to that portion of the brain where we sense hearing, we're going
to hear that as a sound. And sometimes those get crossed. You'll have people that can actually,
they'll hear sounds and it will be like a color. Or they'll smell something and they'll
see a color. And so it's basically action potentials going to the wrong part of your
brain. But that's sensory, that's sensation or excuse me, that's the sensory system. And
I hope that's helpful.