June 28, 2023 • 37 mins
In Episode 139, we explore a new discovery in nerve signaling in the brain called a dendritic action potential (dCaAP), we look at a whacky proposed model of brain function, and we share some ideas about how we can help our students understand the core concepts of chemical signaling and signal transduction in different contexts. Put on your thinking caps and jump into this fresh episode now.
00:00 | Introduction
00:50 | Dendritic Action Potentials
12:16 | Transducer Model of the Brain
21:43 | Chemical Signals & Signal Transduction
35:09 | Staying Connected
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The adage that fact is stranger than fiction seems to be especially true for the workings of the brain. (V.S. Ramachandran)
Dendritic Action Potentials
11.5 minutes
In this segment, the focus is on a fascinating discovery about nerve signaling related to dendritic action potentials (dCaAPs). These unique potentials occur in layers two and three of the human cerebral cortex and play a role in complex brain functions. Unlike typical action potentials, dendritic action potentials are graded and produced by the influx of calcium ions. They enable processing and decision-making at a more complex level, expanding our understanding of the human brain's uniqueness.
★ Scientists Uncover a Never-Before-Seen Type of Signal Occurring in The Human Brain (plain English summary of the new discovery from Science Alert) AandP.info/p08
★ Dendritic action potentials and computation in human layer 2/3 cortical neurons (report in Science) AandP.info/g48
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
>>Kevin Patton:
V.S. (00:00):
undefined
Ramachandran, the prominent neuroscientistand author, once wrote, "The adage that fact
is stranger than fiction seems to be especiallytrue for the workings of the brain."
>>Aileen Park: Welcome to The A&P Professor, a few minutes (00:14):
undefined
to focus on teaching human anatomy and physiologywith a veteran educator and teaching mentor,
your host, Kevin Patton.
>>Kevin Patton: In episode 139, I talk about a new discovery (00:27):
undefined
and nerve signaling in the brain, a possiblenew model of brain function, and how we can
help our students understand core conceptsof chemical signaling and signal transduction.
(00:47):
A couple of years ago, in the journal, Science,there was a very interesting discovery about
nerve signaling that was published.
It has to do with the complexity of brainfunction, specifically in nerve signaling.
Now, this is something that goes beyond thatbasic story of nerve signaling that we tell
(01:10):
our students about how computations work ina nerve network, that is at the neuron level,
neuron and synapse and network level.
We see that there are inputs that come inalong the dendrites and soma, and they may
(01:30):
or may not travel all the way to the axon.
But if they do, it's going to determine whetheran action potential begins in the axon.
And we know that action potentials are allor none events.
So we know if it starts at the beginning ofthe axon near the soma, then we know that
it's going to travel all the way down to theend of the axon.
(01:51):
So what happens in those dendrites reallyis where the decision making is occurring,
where the computation is happening, becausethat's going to determine whether we get a
signal go forward or not.
So we have that.
That's our basic story.
But what they discovered a couple of yearsago is that in layers two and three of the
(02:12):
human cortex, where we have our pyramidalcells and where many neurobiologists believe
the complexity that's going on there is reallywhat makes us uniquely human or makes our
brain a uniquely human brain.
And so what they discovered is dendritic actionpotentials that are occurring there, not the
typical local potentials that we would expectto see along dendrites and the soma in any
(02:39):
part of the nervous system.
These are dendritic action potentials.
And so, yeah, they are going to continue totravel and get to the axon we know.
But an interesting thing about them is that,unlike those other action potentials that
we normally think of, they are graded.
(03:01):
And what that means is that they're not alwaysgoing to get to a certain peak the way we
normally think of an action potential.
They could have a lower amplitude or a higheramplitude, depending on the pathway and the
circumstances and so on.
So that makes it kind of weird.
(03:23):
But that's not the only thing that makes theseweird.
Number one, they're in a dendrite and they'rean action potential.
Number two, they can be graded.
But secondly or thirdly.
Boy, I can't even count.
I don't think my dendritic action potentialsare working.
Thirdly, what triggers them, the mechanismbehind them, maybe is a better way to say
(03:46):
that, is the influx of calcium ions.
Normally when we're looking at an axon, what'sthe mechanism?
It's the influx of sodium ions that causesthat shift in voltage, that becomes the peak
of the action potential.
But in dendritic action potentials, what ishappening is calcium channels are opening,
(04:09):
and calcium influx is what triggers the creationof the instance of a dendritic action potential.
And so that's different.
I mean, that's not highly unusual.
We see calcium causing shifts in membranevoltage in muscle cells, for example.
(04:30):
So yeah, that's something that happens innature, but we didn't expect it to happen
here and under these particular circumstances.
So all of that is kind of weird.
But the importance of it is something that'svery profound, I think.
And that is, it enables processing, decisionmaking at a more complex level and in a simpler
(04:57):
or at least a different way than we expected.
And so this might be part of the key to understandingthe uniqueness of the human brain.
Now, who knows, we might end up finding thisin other brains somewhere else, but then that
would make them complex and in this uniquecategory, I guess, as well.
(05:19):
So how does it do that?
How does it fit in and change that computation?
Well, first of all, we start with this ideaor this model of looking at the brain as if
it were a computer.
And of course, it's not a computer.
And like any model, that falls apart at certainlevels.
But it's a widely used model right now.
(05:41):
When we have nerve signals coming to a neuron,they're going to be coming in by way of synapses
on the dendrites and on the soma.
That's where we're getting signals from otherneurons.
And those signals, they might poop out beforethey get to the axon.
And if so, then that's the decision that weget.
(06:05):
We shut it off.
The switch gets turned off.
And that's partly how computers work withtheir little transistors and so on too.
They're like little gates that acted likea gate that turned off the signal.
If the signal, coming into the dendrite getsto the axon and triggers those voltage-gated
(06:25):
channels there, then we'll have an actionpotential.
And that will get to the distal end of thataxon, and now that's the switch being turned
on.
It's a gateway that allowed the signal toget through.
When we use the lingo of computation, we normallythink of axons as being able to send AND messages
(06:46):
where signals coming in from the dendriteand soma, they are summated and maybe they
work together, and they can send the signalforward.
That is if signal X and signal Y are sent.
Then together, that's enough to trigger thosevoltage-gated channels, and the signal gets
(07:08):
sent forward.
Or we could have a situation where we havemultiple connections to dendrites.
And that's certainly going to happen in thesepyramidal cells in the cortex, layers two
and three of the cortex.
And so we get something called an OR messagepossible.
(07:28):
That's where if we get a signal from one pathway,then that's going to be enough to send the
signal all the way through to get to the beginningof the axon and trigger that action potential
and send it through.
But we could also get a sufficient signalfrom a different pathway.
And when that comes in through the dendriteand gets to the beginning of the axon, if
(07:55):
that's sufficient enough, that's going totrigger the voltage-gated channels.
And yes, we're going to get a signal.
So a shorthand way of saying that is, if weget a signal from X, then the message gets
sent along.
If we get a message from Y, the message getssent along.
So it's X or Y.
(08:16):
So we can set up situations here.
We can set up pathways where you need bothX and Y, and then the signal will get sent.
Or you could set up a situation where eitherX or Y could send the signal forward.
So that gives us quite a bit of flexibilityin how that network is going to work and what
(08:38):
kinds of signaling, what kinds of decisionsare made, what kind of computations are made.
But in complex computer design, there areother kinds of signal processing that can
occur.
And one of those is called the X-OR gateway.
The X stands for exclusive.
(09:00):
So what that means is it's an exclusive-ORoption.
So remember or is X or Y, either one is goingto trigger it.
Exclusive-OR means that X or Y, but the possibilityof turning off X or turning off Y.
(09:24):
So we're going to need another kind of signalthat's happening along with the main signal.
And that signal is going to tamper or modifywhether this signal or that signal, it really
can get the message through.
So I realize I'm oversimplifying this, butthe idea is that those kinds of computations
(09:49):
can happen in the nervous system.
We can see them happening in the nervous system,but only if there is a network of neurons
that are connected with each other and takingon those various aspects.
In other words, that separate signal thatis needed is happening in another neuron,
and that's what's allowing either messageX or message Y from getting through.
(10:14):
Well, here we just have one pyramidal neuronthat's having its usual typical potentials.
Alongside that are these dendritic actionpotentials, and they're acting as the modifier.
So what we're saying is, using just singlecells, we can perform the complex functions
(10:37):
that are associated typically with a networkof neurons.
So how do you pack more neurons into a smallerspace?
Well, you arrange it so you don't need allthose neurons.
So you have neurons that have these weirddendritic action potentials that allow them
(10:57):
to act like multiple neurons, at least interms of their processing power.
So looking at neurons and networks of neuronsas if they were a computer processing system
is a good idea in general.
But there are neurobiologists who get downto this level of figuring out the ons and
(11:21):
offs and modifications of these switches andso on.
And what they're telling us by the discoveryof this dendritic action potential and the
observations they made of them is that, wow,there are some cells that can do some things
that other cells can't, and that makes themwork in a much more complex way than usual.
(11:42):
So circling back to what we tell our students,number one, promise me you're not going to
tell your students about this.
But if they ask, if the discussion goes downthat road, now after having read this research,
you'll be able to say, "Well, yeah, thereare exceptions to these basic principles that
(12:04):
I've been giving you, but they're in veryspecial cells that do very special things,
and possibly exist only in humans."
The computer is often used as a model forthe human nervous system, particularly the
brain and its complex functioning.
I think it's important for us to understandthat that model is a recent model.
(12:32):
In the early days of neurobiology when wewere first beginning to understand that neurons
have a role in the nervous system and whatthat role is and how the nervous system works,
in those early days, we often used a telegraphsystem as a model for the nervous system.
If you're not familiar with a telegraph system,it's simply a wire stretched across a long
(12:55):
distance.
And by creating an electrical signal in thatwire, you can produce a tap or some other
kind of signal at the other end.
So basically, you switch it on, switch iton, switch it on, or switch on, off, on, off.
And a guy named Morse came up with a wholecode, the Morse code, where you could send
(13:19):
telegrams, that is a telegraphic message acrossthe wire where it was just a series of clicks,
short clicks and long clicks, and a certaincombination can be interpreted at the other
end.
And so that was used as a model for sendingsignals in the nervous system.
And then as technology got a little more complexand we started building telephone systems,
(13:43):
we start using that as the model for the humannervous system.
And then as time went by, we realized, well,it's more complex even than that.
And oh, look, we have computers.
That's a good model.
And so there are very many aspects of computerfunction that we're seeing that there are
similar or analogous things happening in thehuman brain.
(14:06):
But as I pointed out way back in episode 112when I was talking about the idea of using
models and codes for things in A&P to helpus understand those things.
And really, models are used a lot in scienceto help scientists understand what it is they're
looking at and form new quests, new questionsthat is, on what to look at next and fill
(14:34):
out and expand those discoveries.
So models are analogies that help us understandthings.
They help us learn things.
They help us discover new things.
But they're just models, they're not the conceptsthemselves.
They're not the discoveries themselves.
So it's important to always be open to settingaside older models and using new models, or
(14:57):
maybe even having several different modelsthat we use to look at several different aspects
of whatever it is we're trying to learn.
So there's that part of it.
But I want to introduce to you a new modelof the human nervous system that is probably
so wacky, it's going to turn out to not beanything close to reality, but it kind of
(15:21):
gives us the idea that there are other waysof thinking about how the nervous system works.
And this comes from an essay written by thepsychologist, Robert Epstein, who's kind of
known for stepping outside of the mainstreamoccasionally and helping us understand things
in a different way and think about thingsin a different way.
(15:45):
And here he is not exactly proposing thisnew model, but setting it out there as something
to just hold onto and think about, and notactually apply to the human brain right now,
but don't disregard it because it could leadus down a pathway that we otherwise wouldn't
have gone down if we're sticking so closelyto that computer model.
(16:08):
And what model is it that he's putting outthere?
He calls it the transducer model.
Now we know what transduction is, right?
We talk about that core concept a lot in humananatomy and physiology.
We talk about how a chemical signal, for example,a neurotransmitter is transduced to become
(16:29):
a signal on the other side of the synapse.
In other words, a neurotransmitter crossesthe synapse, it hits a receptor, signal transduction
occurs in that process of that receptor reaction,and it produces a reaction in the postsynaptic
cell.
We know that hormones are involved in signaltransduction with their target cells and produce
(16:53):
some effect in the target cell.
And we see sensory transduction happen allthe time.
We see where different wavelengths of lightand frequencies of light, they're transduced
into information that eventually gets to ourbrain and is interpreted in a certain way.
Sounds are transduced by the auditory functionsthat begin in our ear.
(17:17):
We have tastes and smells and stress and otherkinds of sensory stimuli that are transduced
and become part of our sensory awareness somewherealong the line.
So what Epstein is saying is, what if we thoughtof the brain as a transducer rather than a
computer, a two-way transducer where it'ssending information out and getting information
(17:43):
back.
So one sort of way that he imagines this isto think of our brain as sort of like a mobile
phone where there's all kinds of things Ican do with my mobile phone.
I can get all kinds of stored information.
And some of that information is actually storedin my phone, but a lot of information I would
(18:06):
need to get from outside the phone.
I would need to tap into a database somewhereon the internet, for example, and search for
that information and find it, and then applyit in whatever way I'm going to apply it.
And he's saying, maybe we do that.
Maybe we send information out of our brainand then bring information back into our brain.
(18:31):
And maybe not everything is stored in ourbrain.
Maybe some things are stored in our brain.
And you know, neuroscience has yet to explainexactly how all of our memories are stored,
the exact mechanisms where they're stored,where they're stored, how they're stored.
Now, a lot of it's been worked out, but notnearly enough to really understand the process.
(18:53):
So he's saying, well, what if we can't understandthe process because we're limiting ourselves
to looking in the brain?
In other words, if we take a mobile phoneand look at it, we can't really explain everything
because not all that information resides there.
Not all of the processing that our searchengine is doing on the internet, that's not
all happening in our phone.
(19:15):
A lot of that's happening somewhere else ona server somewhere.
And so the question then is, where are theservers that our brains are tapping into and
sending information to and getting informationfrom?
And well, that's a big question, isn't it?
That's why we're not adopting this model,are we?
(19:35):
No, because we don't know where that is, orif such a thing exists, such a mechanism exists.
And he throws out there, I don't know if hereally sees it as a serious possibility or
just the idea that science has been discoveringthings beyond our conscious awareness.
And he throws out there this idea of otherdimensions, which physicists, many physicists
(19:59):
at least, will tell you absolutely do exist.
There are these other dimensions, maybe paralleldimensions, maybe there's several possibilities,
some of which apparently have been shown toexist in some way or shape or form.
Can we completely eliminate the idea thatmaybe there's a way that our brain is tapping
(20:20):
into that?
Maybe there's some kind of little quantumthing going on where we're dumping memories
into another dimension, and then when we needthem, we pull them back out of that other
dimension.
Maybe some computations or processing or searchingor some other kind of algorithm is happening
in that other dimension, or a parallel universe,or some sort of shared or networked consciousness,
(20:47):
or who knows?
We don't have to know that part of it yet,not to simply start asking different questions
about the function of the brain that go beyondthe current ways of thinking.
Maybe that's part of why we biologically havehad such a hard time pinning down some of
(21:11):
the complexities of human consciousness andthe evolution of languages and things like
that.
So he is sort of just throwing that out thereas, what if we think about the brain as a
transducer rather than solely as a computer?
And I'm thinking that is wacky.
I'm not ready to adopt it yet.
(21:34):
I bet you aren't either.
But I don't know.
It's just fun to think about, isn't it?
Chemical signaling and transduction of thosechemical signals are core concepts in human
anatomy and physiology that show up time andagain throughout many different topics in
(21:55):
our course.
For example, in the nervous system, when we'retalking about chemical synapses, of course,
there's a neurotransmitter that when it hitsthe postsynaptic membrane, it needs to be
transduced.
And then we get an effect, we get a resultof that signal, we get a reaction to that
(22:16):
signal.
The same thing happens with hormones.
When they hit their target cell, that signalhas to be transduced and then we get a change
in that target cell.
And we see that in the immune system, wherevarious cytokines are sending signals to various
target cells, immune system cells, for example.
(22:40):
And that signal needs to be transduced.
So we see all kinds of signal transductionoccurring in various different ways, shapes
and forms throughout the human body.
And as with any of the core concepts, theseare concepts that we need to help our students
understand are repeating, that they do occurin many different areas of the body.
(23:07):
So when they show up, we need to find waysto help them recognize those core concepts
as concepts they've seen before, as mechanismsthat they've seen operating before, but in
maybe a very different context.
And by doing that, they're going to understandboth contexts, the story that's unfolding
(23:29):
in both contexts much more deeply than theywould have if we keep them separate.
So that's, I think, part of our role as instructors,is to be connectors, to help the students
connect those core concepts.
So I think that should be a goal of ours.
But also, we need to make sure that our studentsknow that that's their goal too, is to connect
(23:55):
those concepts, is to start looking for thoseconnections themselves.
And I've talked about various specific strategiessuch as running concept lists, for example,
and concept mapping, that students can helpthemselves do that and see those connections.
And we can help our students do that by modelingthose strategies ourselves in our teaching
(24:21):
and in our discussions and in our advice thatwe give students in how to study and how to
learn anatomy and physiology.
I also want to point out, at this moment,that transition that we make from nervous
system function to endocrine function in ourcourses, and I realize that not everyone teaches
(24:47):
the topics in exactly the same sequence.
There's sort of a common sequence that manyof us use, but a lot of us modify it from
time to time.
So not everyone does it this way.
But in many A&P courses, a discussion of thenervous system and learning about the nervous
system is then immediately followed by endocrineconcepts and understanding endocrine hormonal
(25:10):
signaling.
And one of the benefits of that is that wecan take this signaling process in one context
that is the nervous system, and transportmany of those core concepts right over to
the discussion of endocrine regulation.
And that transition period where we're justbeginning that discussion of the endocrine
(25:34):
system, having so recently explored the nervoussystem, that's a good place to stop and talk
about connecting the core concepts acrosstopics, and use this as an example of, look
at nerve signaling, look at hormonal signaling.
There are some differences, but there aresome similarities too.
(25:58):
They're basically the same concepts, but they'regoing to play out in different ways and in
different contexts between the two.
And it's not just the concept of signaling,but the structures that are used in signaling.
There's some similarity too.
And let's start there, with structures.
(26:20):
Something that I always point out to my studentsis there are some, what we call endocrine
structures that are producing chemical signalsthat are hormones.
I mean, they literally are hormones becausethey're acting like a hormone.
And that's our definition.
It's a functional definition of a hormone,is a secreting molecule, secreted into the
(26:42):
bloodstream to have an effect outside of thetissue that produced it.
When we are looking at the neurohypophysisand we're looking at the adrenal medulla,
and we look at the pineal gland, and I knowthe other pronunciation is pineal, but I like
pineal because it reminds me of a pine cone,and that's what it's named after.
(27:03):
So all of those glands are really, in a way,modified neurons.
They're secreting what would otherwise beconsidered a neurotransmitter, except that
there's no synapse there.
There's no postsynaptic cell right there.
So they diffuse into the bloodstream, andthen they find that postsynaptic cell, which
(27:24):
is not really postsynaptic because it's notpart of a synapse, it's the target cell.
So that's what replaces the postsynaptic cell,is the target cell.
But it's still signal transduction and stillworks the same way of that other chemical
signal transduction mechanisms work.
At least in general, it works the same way.
(27:48):
So we can see that there is a connection rightaway between those two systems.
Conceptually, at least, there's a connectionbecause some glands really are just modified
presynaptic neurons.
But let's go to the functional side of thingsbecause there, I think, we can even more clearly
(28:09):
see the connection, the conceptual connectionbetween nervous system regulation and endocrine
regulation.
And by doing that, I think our students canmore easily identify the different kinds of
regulation and how the nervous system andendocrine system are complimentary systems
(28:30):
in terms of regulation.
One similarity we can point out is in thenervous system, it's all about regulating
effectors.
And one of the general goals is to help maintainhomeostasis.
And in the endocrine function, we see thatit's regulation of effectors to maintain homeostasis,
(28:53):
it's the same.
So they have the same overall function.
I mean, we're oversimplifying the function,of course, but we're at the beginning of the
story, so we want to do that.
Basically what we're doing is regulating effectorsthroughout the body.
Which one is it, endocrine or nervous systemdoing that?
It's both of them doing that, but they'regoing to be doing it in different ways.
(29:16):
When we look at the endocrine system, we seethat, well, there are regulatory feedback
loops that operate, yeah.
And we can call those endocrine reflexes ifwe want, those feedback loops.
And then we look at the nervous system andwe see, yeah, there are regulatory feedback
loops that operate there too.
And we might call those nerve reflexes whenthose occur.
(29:39):
So yeah, there's some similarity there too,at least in the way the information can be
processed in both those systems.
And then we look at the endocrine system.
It has effector tissues, those we call eitherendocrine effectors or target cells.
Virtually all tissues are target cells ofone or more hormones.
(30:03):
Then we look at the nervous system and wesee, well, there's all kinds of nervous effectors,
and they include mostly muscles and glandulartissue, but we know there's some others like
adipose tissue and so on, but they need tobe connected to the system.
So the endocrine system, these endocrine effectorsand these target cells throughout the body
(30:29):
and the nervous system, well, you got to behooked up to a synapse.
You got to be in the right place at the righttime.
So we're going to see postsynaptic cells beingsort of the target cells of the endocrine
system or equivalent to the target cells inthe endocrine system.
So there's a similarity there too.
(30:51):
I always use a table, by the way, that comparesthe two, and we kind of go through that as
a group, and I sort of unveil the differentrows of the table as we go through so we can
kind of predict and discuss them as we gothrough, so that it's not just reading through
some facts, but actually figuring out thefacts.
And then like, oh, yes, we were right.
(31:11):
Sort of like in Jeopardy, oh, I guessed right.
Another thing that we can look at is the chemicalmessenger itself.
In both places you have a chemical messenger,right?
In the endocrine system, the chemical messengersare called hormones.
And in the nervous system, the chemical messengersare called neurotransmitters.
So in that way, they're alike.
(31:32):
And we have, in both systems, cells that secretethe chemical messenger.
So those would be either the glandular epithelialcells or the neurosecretory cells, if we're
talking about the endocrine system.
And if we're talking about the nervous system,those are the neurons, the presynaptic neurons.
(31:53):
And then here's a big difference between thetwo.
If we look at the distance traveled by thatchemical messenger and the method of travel
of that chemical messenger, now we see somebig differences.
In the endocrine system, it's a long distancethat's traveled by the hormone, and the method
is by way of the circulating blood.
(32:16):
The nervous system on the other hand, hasa short distance for that chemical messenger
to travel.
That neurotransmitter goes across a microscopicsynapse.
And so that's diffusion and it's a short distance.
So there's a contrast there between the two.
And then we look at, well, where are the receptorslocated in the effector cell?
(32:40):
Well, in the endocrine system, on the plasmamembrane or within the cell is where we're
going to be finding those receptors.
And it's pretty similar in the nervous system.
It's just on the plasma membrane, we're notgoing to be receiving the neurotransmitters
inside the postsynaptic cell, even thoughthat's an option in the endocrine system.
(33:04):
So again, we're back to really pretty similarscenarios or strategies or mechanisms that
are operating there.
And then we look at the characteristics ofregulatory effects.
And in the nervous system, the students would'velearned that the effects usually appear rapidly,
(33:25):
but they're short-lived.
Unless we keep them going, they don't lastvery long.
And now that's in general, of course.
And then we look at the endocrine system andwe say, well, it takes longer for them to
appear because they have to get into the bloodsupply, they have to circulate around, finally
hit their target cell.
So it just physically is a longer distance.
(33:47):
So yeah, it's going to take longer for theregulatory effects to appear, but because
the hormones kind of linger for a while andthey don't all hit the target cells right
away, and they kind of go back around againand come back.
And yeah, there might still be some left inthe blood there, they're prolonging that effect.
Now, within that group, when we look at hormones,we see that some produce effects sooner than
(34:14):
others, some last longer than others.
So yeah, there's a range of activity withinthat.
But when you're just looking at a very simplelevel and comparing endocrine versus nervous,
we can say that endocrine is slow, but long-lasting.
And nervous system effects, they appear rapidly,and they're short-lived.
(34:35):
That's just kind of an approach.
It may or may not fit into the way you dothings in your course, but I think that's
a good opportunity for us to not only makethat transition from nervous system to endocrine,
but in doing so, look at some of these coreconcepts of chemical signaling and signal
transduction and how they operate similarlyin the two different systems, and how they
(35:01):
also sometimes play out differently in thetwo different systems.
Well, let's see.
In episode 139, I put on my thinking cap andshared some ideas about how we can help our
students understand the core concepts of chemicalsignaling and signal transduction in different
(35:25):
contexts.
And before that, I briefly described the transducermodel of brain function, a wacky new idea
that psychologist, Robert Epstein, thinksmay help us work out where we're stuck in
understanding how the nervous system works,and especially the brain, in those complex
(35:47):
ways that are uniquely human.
And we started this episode with a new discoveryand nerve signaling in the brain called dendritic
action potentials that involve the calciummechanism instead of the sodium mechanism,
and may help explain the complexity of humancortical function.
(36:12):
Now, as always, I have links for you for allthese topics.
If you don't see links in your podcast player,go to the episode page at theAPprofessor.org/139.
And while you're there, you can claim yourdigital credential for listening to this episode.
(36:35):
And don't forget to call in.
Please call in with your anecdotes, tips,and questions at the podcast hotline.
That's 1-833-LION-DEN, or 1-833-546-6336.
Or send a recording or a written message topodcast@theAPprofessor.org.
(36:58):
I'll see you down the road.
>>Aileen Park: The A&P Professor is hosted by Dr. Kevin Patton, (37:06):
undefined
an award-winning professor and textbook authorin human anatomy and physiology.
>>Kevin Patton: Listening to this episode may cause permanent (37:15):
undefined
changes in the brain.
undefined
Ramachandran, the prominent neuroscientistand author, once wrote, "The adage that fact
is stranger than fiction seems to be especiallytrue for the workings of the brain."
>>Aileen Park: Welcome to The A&P Professor, a few minutes (00:14):
undefined
to focus on teaching human anatomy and physiologywith a veteran educator and teaching mentor,
your host, Kevin Patton.
>>Kevin Patton: In episode 139, I talk about a new discovery (00:27):
undefined
and nerve signaling in the brain, a possiblenew model of brain function, and how we can
help our students understand core conceptsof chemical signaling and signal transduction.
(00:47):
A couple of years ago, in the journal, Science,there was a very interesting discovery about
nerve signaling that was published.
It has to do with the complexity of brainfunction, specifically in nerve signaling.
Now, this is something that goes beyond thatbasic story of nerve signaling that we tell
(01:10):
our students about how computations work ina nerve network, that is at the neuron level,
neuron and synapse and network level.
We see that there are inputs that come inalong the dendrites and soma, and they may
(01:30):
or may not travel all the way to the axon.
But if they do, it's going to determine whetheran action potential begins in the axon.
And we know that action potentials are allor none events.
So we know if it starts at the beginning ofthe axon near the soma, then we know that
it's going to travel all the way down to theend of the axon.
(01:51):
So what happens in those dendrites reallyis where the decision making is occurring,
where the computation is happening, becausethat's going to determine whether we get a
signal go forward or not.
So we have that.
That's our basic story.
But what they discovered a couple of yearsago is that in layers two and three of the
(02:12):
human cortex, where we have our pyramidalcells and where many neurobiologists believe
the complexity that's going on there is reallywhat makes us uniquely human or makes our
brain a uniquely human brain.
And so what they discovered is dendritic actionpotentials that are occurring there, not the
typical local potentials that we would expectto see along dendrites and the soma in any
(02:39):
part of the nervous system.
These are dendritic action potentials.
And so, yeah, they are going to continue totravel and get to the axon we know.
But an interesting thing about them is that,unlike those other action potentials that
we normally think of, they are graded.
(03:01):
And what that means is that they're not alwaysgoing to get to a certain peak the way we
normally think of an action potential.
They could have a lower amplitude or a higheramplitude, depending on the pathway and the
circumstances and so on.
So that makes it kind of weird.
(03:23):
But that's not the only thing that makes theseweird.
Number one, they're in a dendrite and they'rean action potential.
Number two, they can be graded.
But secondly or thirdly.
Boy, I can't even count.
I don't think my dendritic action potentialsare working.
Thirdly, what triggers them, the mechanismbehind them, maybe is a better way to say
(03:46):
that, is the influx of calcium ions.
Normally when we're looking at an axon, what'sthe mechanism?
It's the influx of sodium ions that causesthat shift in voltage, that becomes the peak
of the action potential.
But in dendritic action potentials, what ishappening is calcium channels are opening,
(04:09):
and calcium influx is what triggers the creationof the instance of a dendritic action potential.
And so that's different.
I mean, that's not highly unusual.
We see calcium causing shifts in membranevoltage in muscle cells, for example.
(04:30):
So yeah, that's something that happens innature, but we didn't expect it to happen
here and under these particular circumstances.
So all of that is kind of weird.
But the importance of it is something that'svery profound, I think.
And that is, it enables processing, decisionmaking at a more complex level and in a simpler
(04:57):
or at least a different way than we expected.
And so this might be part of the key to understandingthe uniqueness of the human brain.
Now, who knows, we might end up finding thisin other brains somewhere else, but then that
would make them complex and in this uniquecategory, I guess, as well.
(05:19):
So how does it do that?
How does it fit in and change that computation?
Well, first of all, we start with this ideaor this model of looking at the brain as if
it were a computer.
And of course, it's not a computer.
And like any model, that falls apart at certainlevels.
But it's a widely used model right now.
(05:41):
When we have nerve signals coming to a neuron,they're going to be coming in by way of synapses
on the dendrites and on the soma.
That's where we're getting signals from otherneurons.
And those signals, they might poop out beforethey get to the axon.
And if so, then that's the decision that weget.
(06:05):
We shut it off.
The switch gets turned off.
And that's partly how computers work withtheir little transistors and so on too.
They're like little gates that acted likea gate that turned off the signal.
If the signal, coming into the dendrite getsto the axon and triggers those voltage-gated
(06:25):
channels there, then we'll have an actionpotential.
And that will get to the distal end of thataxon, and now that's the switch being turned
on.
It's a gateway that allowed the signal toget through.
When we use the lingo of computation, we normallythink of axons as being able to send AND messages
(06:46):
where signals coming in from the dendriteand soma, they are summated and maybe they
work together, and they can send the signalforward.
That is if signal X and signal Y are sent.
Then together, that's enough to trigger thosevoltage-gated channels, and the signal gets
(07:08):
sent forward.
Or we could have a situation where we havemultiple connections to dendrites.
And that's certainly going to happen in thesepyramidal cells in the cortex, layers two
and three of the cortex.
And so we get something called an OR messagepossible.
(07:28):
That's where if we get a signal from one pathway,then that's going to be enough to send the
signal all the way through to get to the beginningof the axon and trigger that action potential
and send it through.
But we could also get a sufficient signalfrom a different pathway.
And when that comes in through the dendriteand gets to the beginning of the axon, if
(07:55):
that's sufficient enough, that's going totrigger the voltage-gated channels.
And yes, we're going to get a signal.
So a shorthand way of saying that is, if weget a signal from X, then the message gets
sent along.
If we get a message from Y, the message getssent along.
So it's X or Y.
(08:16):
So we can set up situations here.
We can set up pathways where you need bothX and Y, and then the signal will get sent.
Or you could set up a situation where eitherX or Y could send the signal forward.
So that gives us quite a bit of flexibilityin how that network is going to work and what
(08:38):
kinds of signaling, what kinds of decisionsare made, what kind of computations are made.
But in complex computer design, there areother kinds of signal processing that can
occur.
And one of those is called the X-OR gateway.
The X stands for exclusive.
(09:00):
So what that means is it's an exclusive-ORoption.
So remember or is X or Y, either one is goingto trigger it.
Exclusive-OR means that X or Y, but the possibilityof turning off X or turning off Y.
(09:24):
So we're going to need another kind of signalthat's happening along with the main signal.
And that signal is going to tamper or modifywhether this signal or that signal, it really
can get the message through.
So I realize I'm oversimplifying this, butthe idea is that those kinds of computations
(09:49):
can happen in the nervous system.
We can see them happening in the nervous system,but only if there is a network of neurons
that are connected with each other and takingon those various aspects.
In other words, that separate signal thatis needed is happening in another neuron,
and that's what's allowing either messageX or message Y from getting through.
(10:14):
Well, here we just have one pyramidal neuronthat's having its usual typical potentials.
Alongside that are these dendritic actionpotentials, and they're acting as the modifier.
So what we're saying is, using just singlecells, we can perform the complex functions
(10:37):
that are associated typically with a networkof neurons.
So how do you pack more neurons into a smallerspace?
Well, you arrange it so you don't need allthose neurons.
So you have neurons that have these weirddendritic action potentials that allow them
(10:57):
to act like multiple neurons, at least interms of their processing power.
So looking at neurons and networks of neuronsas if they were a computer processing system
is a good idea in general.
But there are neurobiologists who get downto this level of figuring out the ons and
(11:21):
offs and modifications of these switches andso on.
And what they're telling us by the discoveryof this dendritic action potential and the
observations they made of them is that, wow,there are some cells that can do some things
that other cells can't, and that makes themwork in a much more complex way than usual.
(11:42):
So circling back to what we tell our students,number one, promise me you're not going to
tell your students about this.
But if they ask, if the discussion goes downthat road, now after having read this research,
you'll be able to say, "Well, yeah, thereare exceptions to these basic principles that
(12:04):
I've been giving you, but they're in veryspecial cells that do very special things,
and possibly exist only in humans."
The computer is often used as a model forthe human nervous system, particularly the
brain and its complex functioning.
I think it's important for us to understandthat that model is a recent model.
(12:32):
In the early days of neurobiology when wewere first beginning to understand that neurons
have a role in the nervous system and whatthat role is and how the nervous system works,
in those early days, we often used a telegraphsystem as a model for the nervous system.
If you're not familiar with a telegraph system,it's simply a wire stretched across a long
(12:55):
distance.
And by creating an electrical signal in thatwire, you can produce a tap or some other
kind of signal at the other end.
So basically, you switch it on, switch iton, switch it on, or switch on, off, on, off.
And a guy named Morse came up with a wholecode, the Morse code, where you could send
(13:19):
telegrams, that is a telegraphic message acrossthe wire where it was just a series of clicks,
short clicks and long clicks, and a certaincombination can be interpreted at the other
end.
And so that was used as a model for sendingsignals in the nervous system.
And then as technology got a little more complexand we started building telephone systems,
(13:43):
we start using that as the model for the humannervous system.
And then as time went by, we realized, well,it's more complex even than that.
And oh, look, we have computers.
That's a good model.
And so there are very many aspects of computerfunction that we're seeing that there are
similar or analogous things happening in thehuman brain.
(14:06):
But as I pointed out way back in episode 112when I was talking about the idea of using
models and codes for things in A&P to helpus understand those things.
And really, models are used a lot in scienceto help scientists understand what it is they're
looking at and form new quests, new questionsthat is, on what to look at next and fill
(14:34):
out and expand those discoveries.
So models are analogies that help us understandthings.
They help us learn things.
They help us discover new things.
But they're just models, they're not the conceptsthemselves.
They're not the discoveries themselves.
So it's important to always be open to settingaside older models and using new models, or
(14:57):
maybe even having several different modelsthat we use to look at several different aspects
of whatever it is we're trying to learn.
So there's that part of it.
But I want to introduce to you a new modelof the human nervous system that is probably
so wacky, it's going to turn out to not beanything close to reality, but it kind of
(15:21):
gives us the idea that there are other waysof thinking about how the nervous system works.
And this comes from an essay written by thepsychologist, Robert Epstein, who's kind of
known for stepping outside of the mainstreamoccasionally and helping us understand things
in a different way and think about thingsin a different way.
(15:45):
And here he is not exactly proposing thisnew model, but setting it out there as something
to just hold onto and think about, and notactually apply to the human brain right now,
but don't disregard it because it could leadus down a pathway that we otherwise wouldn't
have gone down if we're sticking so closelyto that computer model.
(16:08):
And what model is it that he's putting outthere?
He calls it the transducer model.
Now we know what transduction is, right?
We talk about that core concept a lot in humananatomy and physiology.
We talk about how a chemical signal, for example,a neurotransmitter is transduced to become
(16:29):
a signal on the other side of the synapse.
In other words, a neurotransmitter crossesthe synapse, it hits a receptor, signal transduction
occurs in that process of that receptor reaction,and it produces a reaction in the postsynaptic
cell.
We know that hormones are involved in signaltransduction with their target cells and produce
(16:53):
some effect in the target cell.
And we see sensory transduction happen allthe time.
We see where different wavelengths of lightand frequencies of light, they're transduced
into information that eventually gets to ourbrain and is interpreted in a certain way.
Sounds are transduced by the auditory functionsthat begin in our ear.
(17:17):
We have tastes and smells and stress and otherkinds of sensory stimuli that are transduced
and become part of our sensory awareness somewherealong the line.
So what Epstein is saying is, what if we thoughtof the brain as a transducer rather than a
computer, a two-way transducer where it'ssending information out and getting information
(17:43):
back.
So one sort of way that he imagines this isto think of our brain as sort of like a mobile
phone where there's all kinds of things Ican do with my mobile phone.
I can get all kinds of stored information.
And some of that information is actually storedin my phone, but a lot of information I would
(18:06):
need to get from outside the phone.
I would need to tap into a database somewhereon the internet, for example, and search for
that information and find it, and then applyit in whatever way I'm going to apply it.
And he's saying, maybe we do that.
Maybe we send information out of our brainand then bring information back into our brain.
(18:31):
And maybe not everything is stored in ourbrain.
Maybe some things are stored in our brain.
And you know, neuroscience has yet to explainexactly how all of our memories are stored,
the exact mechanisms where they're stored,where they're stored, how they're stored.
Now, a lot of it's been worked out, but notnearly enough to really understand the process.
(18:53):
So he's saying, well, what if we can't understandthe process because we're limiting ourselves
to looking in the brain?
In other words, if we take a mobile phoneand look at it, we can't really explain everything
because not all that information resides there.
Not all of the processing that our searchengine is doing on the internet, that's not
all happening in our phone.
(19:15):
A lot of that's happening somewhere else ona server somewhere.
And so the question then is, where are theservers that our brains are tapping into and
sending information to and getting informationfrom?
And well, that's a big question, isn't it?
That's why we're not adopting this model,are we?
(19:35):
No, because we don't know where that is, orif such a thing exists, such a mechanism exists.
And he throws out there, I don't know if hereally sees it as a serious possibility or
just the idea that science has been discoveringthings beyond our conscious awareness.
And he throws out there this idea of otherdimensions, which physicists, many physicists
(19:59):
at least, will tell you absolutely do exist.
There are these other dimensions, maybe paralleldimensions, maybe there's several possibilities,
some of which apparently have been shown toexist in some way or shape or form.
Can we completely eliminate the idea thatmaybe there's a way that our brain is tapping
(20:20):
into that?
Maybe there's some kind of little quantumthing going on where we're dumping memories
into another dimension, and then when we needthem, we pull them back out of that other
dimension.
Maybe some computations or processing or searchingor some other kind of algorithm is happening
in that other dimension, or a parallel universe,or some sort of shared or networked consciousness,
(20:47):
or who knows?
We don't have to know that part of it yet,not to simply start asking different questions
about the function of the brain that go beyondthe current ways of thinking.
Maybe that's part of why we biologically havehad such a hard time pinning down some of
(21:11):
the complexities of human consciousness andthe evolution of languages and things like
that.
So he is sort of just throwing that out thereas, what if we think about the brain as a
transducer rather than solely as a computer?
And I'm thinking that is wacky.
I'm not ready to adopt it yet.
(21:34):
I bet you aren't either.
But I don't know.
It's just fun to think about, isn't it?
Chemical signaling and transduction of thosechemical signals are core concepts in human
anatomy and physiology that show up time andagain throughout many different topics in
(21:55):
our course.
For example, in the nervous system, when we'retalking about chemical synapses, of course,
there's a neurotransmitter that when it hitsthe postsynaptic membrane, it needs to be
transduced.
And then we get an effect, we get a resultof that signal, we get a reaction to that
(22:16):
signal.
The same thing happens with hormones.
When they hit their target cell, that signalhas to be transduced and then we get a change
in that target cell.
And we see that in the immune system, wherevarious cytokines are sending signals to various
target cells, immune system cells, for example.
(22:40):
And that signal needs to be transduced.
So we see all kinds of signal transductionoccurring in various different ways, shapes
and forms throughout the human body.
And as with any of the core concepts, theseare concepts that we need to help our students
understand are repeating, that they do occurin many different areas of the body.
(23:07):
So when they show up, we need to find waysto help them recognize those core concepts
as concepts they've seen before, as mechanismsthat they've seen operating before, but in
maybe a very different context.
And by doing that, they're going to understandboth contexts, the story that's unfolding
(23:29):
in both contexts much more deeply than theywould have if we keep them separate.
So that's, I think, part of our role as instructors,is to be connectors, to help the students
connect those core concepts.
So I think that should be a goal of ours.
But also, we need to make sure that our studentsknow that that's their goal too, is to connect
(23:55):
those concepts, is to start looking for thoseconnections themselves.
And I've talked about various specific strategiessuch as running concept lists, for example,
and concept mapping, that students can helpthemselves do that and see those connections.
And we can help our students do that by modelingthose strategies ourselves in our teaching
(24:21):
and in our discussions and in our advice thatwe give students in how to study and how to
learn anatomy and physiology.
I also want to point out, at this moment,that transition that we make from nervous
system function to endocrine function in ourcourses, and I realize that not everyone teaches
(24:47):
the topics in exactly the same sequence.
There's sort of a common sequence that manyof us use, but a lot of us modify it from
time to time.
So not everyone does it this way.
But in many A&P courses, a discussion of thenervous system and learning about the nervous
system is then immediately followed by endocrineconcepts and understanding endocrine hormonal
(25:10):
signaling.
And one of the benefits of that is that wecan take this signaling process in one context
that is the nervous system, and transportmany of those core concepts right over to
the discussion of endocrine regulation.
And that transition period where we're justbeginning that discussion of the endocrine
(25:34):
system, having so recently explored the nervoussystem, that's a good place to stop and talk
about connecting the core concepts acrosstopics, and use this as an example of, look
at nerve signaling, look at hormonal signaling.
There are some differences, but there aresome similarities too.
(25:58):
They're basically the same concepts, but they'regoing to play out in different ways and in
different contexts between the two.
And it's not just the concept of signaling,but the structures that are used in signaling.
There's some similarity too.
And let's start there, with structures.
(26:20):
Something that I always point out to my studentsis there are some, what we call endocrine
structures that are producing chemical signalsthat are hormones.
I mean, they literally are hormones becausethey're acting like a hormone.
And that's our definition.
It's a functional definition of a hormone,is a secreting molecule, secreted into the
(26:42):
bloodstream to have an effect outside of thetissue that produced it.
When we are looking at the neurohypophysisand we're looking at the adrenal medulla,
and we look at the pineal gland, and I knowthe other pronunciation is pineal, but I like
pineal because it reminds me of a pine cone,and that's what it's named after.
(27:03):
So all of those glands are really, in a way,modified neurons.
They're secreting what would otherwise beconsidered a neurotransmitter, except that
there's no synapse there.
There's no postsynaptic cell right there.
So they diffuse into the bloodstream, andthen they find that postsynaptic cell, which
(27:24):
is not really postsynaptic because it's notpart of a synapse, it's the target cell.
So that's what replaces the postsynaptic cell,is the target cell.
But it's still signal transduction and stillworks the same way of that other chemical
signal transduction mechanisms work.
At least in general, it works the same way.
(27:48):
So we can see that there is a connection rightaway between those two systems.
Conceptually, at least, there's a connectionbecause some glands really are just modified
presynaptic neurons.
But let's go to the functional side of thingsbecause there, I think, we can even more clearly
(28:09):
see the connection, the conceptual connectionbetween nervous system regulation and endocrine
regulation.
And by doing that, I think our students canmore easily identify the different kinds of
regulation and how the nervous system andendocrine system are complimentary systems
(28:30):
in terms of regulation.
One similarity we can point out is in thenervous system, it's all about regulating
effectors.
And one of the general goals is to help maintainhomeostasis.
And in the endocrine function, we see thatit's regulation of effectors to maintain homeostasis,
(28:53):
it's the same.
So they have the same overall function.
I mean, we're oversimplifying the function,of course, but we're at the beginning of the
story, so we want to do that.
Basically what we're doing is regulating effectorsthroughout the body.
Which one is it, endocrine or nervous systemdoing that?
It's both of them doing that, but they'regoing to be doing it in different ways.
(29:16):
When we look at the endocrine system, we seethat, well, there are regulatory feedback
loops that operate, yeah.
And we can call those endocrine reflexes ifwe want, those feedback loops.
And then we look at the nervous system andwe see, yeah, there are regulatory feedback
loops that operate there too.
And we might call those nerve reflexes whenthose occur.
(29:39):
So yeah, there's some similarity there too,at least in the way the information can be
processed in both those systems.
And then we look at the endocrine system.
It has effector tissues, those we call eitherendocrine effectors or target cells.
Virtually all tissues are target cells ofone or more hormones.
(30:03):
Then we look at the nervous system and wesee, well, there's all kinds of nervous effectors,
and they include mostly muscles and glandulartissue, but we know there's some others like
adipose tissue and so on, but they need tobe connected to the system.
So the endocrine system, these endocrine effectorsand these target cells throughout the body
(30:29):
and the nervous system, well, you got to behooked up to a synapse.
You got to be in the right place at the righttime.
So we're going to see postsynaptic cells beingsort of the target cells of the endocrine
system or equivalent to the target cells inthe endocrine system.
So there's a similarity there too.
(30:51):
I always use a table, by the way, that comparesthe two, and we kind of go through that as
a group, and I sort of unveil the differentrows of the table as we go through so we can
kind of predict and discuss them as we gothrough, so that it's not just reading through
some facts, but actually figuring out thefacts.
And then like, oh, yes, we were right.
(31:11):
Sort of like in Jeopardy, oh, I guessed right.
Another thing that we can look at is the chemicalmessenger itself.
In both places you have a chemical messenger,right?
In the endocrine system, the chemical messengersare called hormones.
And in the nervous system, the chemical messengersare called neurotransmitters.
So in that way, they're alike.
(31:32):
And we have, in both systems, cells that secretethe chemical messenger.
So those would be either the glandular epithelialcells or the neurosecretory cells, if we're
talking about the endocrine system.
And if we're talking about the nervous system,those are the neurons, the presynaptic neurons.
(31:53):
And then here's a big difference between thetwo.
If we look at the distance traveled by thatchemical messenger and the method of travel
of that chemical messenger, now we see somebig differences.
In the endocrine system, it's a long distancethat's traveled by the hormone, and the method
is by way of the circulating blood.
(32:16):
The nervous system on the other hand, hasa short distance for that chemical messenger
to travel.
That neurotransmitter goes across a microscopicsynapse.
And so that's diffusion and it's a short distance.
So there's a contrast there between the two.
And then we look at, well, where are the receptorslocated in the effector cell?
(32:40):
Well, in the endocrine system, on the plasmamembrane or within the cell is where we're
going to be finding those receptors.
And it's pretty similar in the nervous system.
It's just on the plasma membrane, we're notgoing to be receiving the neurotransmitters
inside the postsynaptic cell, even thoughthat's an option in the endocrine system.
(33:04):
So again, we're back to really pretty similarscenarios or strategies or mechanisms that
are operating there.
And then we look at the characteristics ofregulatory effects.
And in the nervous system, the students would'velearned that the effects usually appear rapidly,
(33:25):
but they're short-lived.
Unless we keep them going, they don't lastvery long.
And now that's in general, of course.
And then we look at the endocrine system andwe say, well, it takes longer for them to
appear because they have to get into the bloodsupply, they have to circulate around, finally
hit their target cell.
So it just physically is a longer distance.
(33:47):
So yeah, it's going to take longer for theregulatory effects to appear, but because
the hormones kind of linger for a while andthey don't all hit the target cells right
away, and they kind of go back around againand come back.
And yeah, there might still be some left inthe blood there, they're prolonging that effect.
Now, within that group, when we look at hormones,we see that some produce effects sooner than
(34:14):
others, some last longer than others.
So yeah, there's a range of activity withinthat.
But when you're just looking at a very simplelevel and comparing endocrine versus nervous,
we can say that endocrine is slow, but long-lasting.
And nervous system effects, they appear rapidly,and they're short-lived.
(34:35):
That's just kind of an approach.
It may or may not fit into the way you dothings in your course, but I think that's
a good opportunity for us to not only makethat transition from nervous system to endocrine,
but in doing so, look at some of these coreconcepts of chemical signaling and signal
transduction and how they operate similarlyin the two different systems, and how they
(35:01):
also sometimes play out differently in thetwo different systems.
Well, let's see.
In episode 139, I put on my thinking cap andshared some ideas about how we can help our
students understand the core concepts of chemicalsignaling and signal transduction in different
(35:25):
contexts.
And before that, I briefly described the transducermodel of brain function, a wacky new idea
that psychologist, Robert Epstein, thinksmay help us work out where we're stuck in
understanding how the nervous system works,and especially the brain, in those complex
(35:47):
ways that are uniquely human.
And we started this episode with a new discoveryand nerve signaling in the brain called dendritic
action potentials that involve the calciummechanism instead of the sodium mechanism,
and may help explain the complexity of humancortical function.
(36:12):
Now, as always, I have links for you for allthese topics.
If you don't see links in your podcast player,go to the episode page at theAPprofessor.org/139.
And while you're there, you can claim yourdigital credential for listening to this episode.
(36:35):
And don't forget to call in.
Please call in with your anecdotes, tips,and questions at the podcast hotline.
That's 1-833-LION-DEN, or 1-833-546-6336.
Or send a recording or a written message topodcast@theAPprofessor.org.
(36:58):
I'll see you down the road.
>>Aileen Park: The A&P Professor is hosted by Dr. Kevin Patton, (37:06):
undefined
an award-winning professor and textbook authorin human anatomy and physiology.
>>Kevin Patton: Listening to this episode may cause permanent (37:15):
undefined
changes in the brain.
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