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0:07Hello everyone, young friends. We are
0:09continuing our AYT camp. 12th. grade
0:11topics are completed. Now we are
0:13starting the 11th. grade. We will finish
0:15two units here, young friends, but one
0:17is very long, of course.
0:19It has too many subheadings and topics,
0:21but fortunately, it's a place we enjoy.
0:2311th. grade, young friends, what will we
0:25learn first in the unit? We will call it
0:27human physiology. Then, with community
0:29and population ecology, we will have
0:31completed the camp. Since we finished
0:32the 12th grade material. Where will the
0:34first topic in human physiology come
0:36from? As you can see on the board, young
0:38friends, we will start with the nervous
0:40system, but I have, of course, divided
0:42the nervous system topic into parts.
0:43What will we do first? We will look at
0:46the structure, function, and operation
0:47of the nervous system. Then, we will
0:49complete this as central and peripheral
0:52.
0:52You know we did dissections in our
0:54classes last year as well. I mean, I
0:56brought the structures I could find, as
0:58much as possible, and explained them to
1:00you by doing experiments here. You are
1:02asking if we will do it this year, too.
1:04We will, young friends. I will even
1:05change the format a bit more.
1:07But today, let's first lay the basic
1:09structure of this nervous system.
1:11Let's get to know this part. I mean,
1:13what is our nervous system? What
1:14structures is it composed of? What will
1:16we see? Let's see them together in part
1:181, young friends. Then we will see it as
1:21central and peripheral.
1:23Now, friends, actually, we are starting
1:25with our first topic, the nervous system
1:27, but this is usually taught as
1:29regulatory and control systems.
1:32Regulatory and control systems also
1:33include the nervous and endocrine
1:34systems within themselves.
1:37Therefore, after I explain the nervous
1:39system to you, our next topic will be
1:41the endocrine system.
1:43Why is it like this? Because it says
1:45regulatory and control systems. So, we,
1:48as living things—since this is human
1:50physiology, I will speak directly about
1:52humans—what do we do?
1:54What do we do? We respond in two ways.
1:57One is neural, meaning sudden and fast.
2:00Then, there is also hormonal, meaning
2:02slower, later-appearing responses we
2:04give through the endocrine system; so
2:06when it says regulatory and control
2:08systems, we will know it covers both of
2:10these, okay, young friends?
2:12Let's start with the structure, function
2:14, and operation of the nervous system
2:15first. I will give you some concepts. We
2:18will go through them by underlining them
2:19, young friends. Because we will use
2:21these concepts a lot in what follows.
2:24Let's look right here at the structure
2:26of the nervous system: friends, we call
2:28the specialized cells found in sensory
2:30organs that receive stimulating effects
2:32like light, sound, and chemical
2:34substances around living things the
2:36receptor, or receiving cell, which is
2:38generally located there.
2:40As soon as you see the word receptor,
2:42you will say, "Teacher, he's talking
2:44about the receiver." It perceives the
2:46incoming stimulus.
2:47Stimuli cause the initiation of the
2:49stimulus in receptor cells. Meaning, it
2:51says it stimulates that cell.
2:54These stimuli, transmitted to the
2:55central nervous system by nerve cells,
2:57are interpreted there and a response is
2:59generated.
3:01So, you bring it to the central nervous
3:03system. Look, this part is important now
3:04. You are learning it here for the first
3:06time. We will repeat it. Friends, when
3:08we say CNS in humans, that is the
3:10central nervous system, you must know
3:12that it covers the brain and the spinal
3:14cord. Our brain and our spinal cord make
3:16up the central nervous system.
3:19We call organs like muscles or glands
3:22that generate a response to stimuli
3:25processed in the central nervous system
3:28effectors.
3:30We will use this term, too. I want you
3:31to put a star next to this.
3:33So, the thing that generates your
3:35response—when I give a neural or
3:36hormonal response, I do it either with
3:38my muscles or my secretory glands.
3:41We will call this the effector, guys.
3:43The receptor received it. The effector
3:44became the organ that formed the
3:46response. The nervous system is composed
3:49of neurons, which are nerve cells, and
3:51glia, which are helper cells. This is
3:53very important; we will talk about these
3:56first throughout this lesson. It’s not
3:58just neurons here, guys. Look, we will
4:01encounter this in every topic regarding
4:04nerve cells.
4:06If there are specialized cells, meaning
4:08they have a specific task, we give those
4:10cells names.
4:11We will call nerve cells neurons, and
4:14neurons are not alone; they have helpers
4:17, the glia, guys. It is very important.
4:20Come, let's remember the functions and
4:22types of glia together.
4:24Now, these are helper structures that
4:26fill the spaces between neurons. They
4:28have the ability to divide. They are
4:30more numerous than neurons.
4:32I mean, we actually say nerve cells
4:33don't divide, but we are referring to a
4:35specific part there.
4:37They do not have impulse events, guys.
4:39While only Schwann cells are found in
4:41the peripheral nervous system, we will
4:43see other glial cells in the central
4:45nervous system, and we must know the
4:46importance of each one's task, guys.
4:48There are especially two that are
4:50generally compared. You knew it as soon
4:53as you saw it on the board. Schwann cell
4:55is the most famous one, guys. The one it
4:57is compared to is the oligodendrocyte.
4:59Why? Let's see right away. Both of their
5:01functions are common, but their
5:03locations and structures are different.
5:05Both form the myelin sheath. Now you
5:07will say, "Teacher, what is a myelin
5:09sheath?" Myelin sheath, guys, I will
5:10explain it in the following slides as
5:12well.
5:13It is actually a sheath we see in some
5:15neurons that accelerates transmission.
5:17It is a lipoprotein-structured sheath,
5:20and if they ask for the glia that forms
5:22this in the peripheral nervous system,
5:25don't forget, for PNS, it will be
5:27Schwann, guys.
5:29But if there is a myelin sheath in a
5:31neuron in the central nervous system,
5:33the name of the glial type that forms
5:35this will be oligodendrocyte.
5:37You will know that oligodendrocyte
5:39belongs to the CNS and Schwann belongs
5:41to the PNS. I will abbreviate central as
5:43CNS and will always call peripheral PNS
5:45. When I use these, understand what I
5:47mean. I am coming to microglia. They
5:50ensure the defense of the nervous system
5:51by performing phagocytosis, meaning they
5:53protect that area. What does
5:55phagocytosis mean?
5:57Swallowing a large solid thing; meaning
5:59when it sees a microorganism or
6:00something that will harm it, it swallows
6:02it into the system and actually protects
6:05itself.
6:06Because protecting your central nervous
6:07system is very important. The basic
6:09control mechanism of the entire system
6:11is here, guys.
6:12I am continuing with my glia. We will
6:14see my ependymal cells and astrocytes,
6:17guys. Ependymal cells do this. CSF fluid
6:20. You are encountering it for the first
6:21time. Star it, underline it. Because you
6:23will see it more often from now on. Guys
6:25, the thing we abbreviate as CSF is
6:28cerebrospinal fluid. Since it is found
6:31in both places, its name is like this,
6:32and here, what is the reason it is
6:34called central nervous system, guys?
6:36Because the brain and spinal cord belong
6:38here. It lines the cavities of the
6:40central nervous system and at the same
6:42time, with CSF production, it regulates
6:44this flow, guys. Production and flow of
6:47CSF. Remember, when ependyma is
6:48mentioned, we immediately say CSF. Look
6:50, astrocytes are right there on the
6:52other side. These perform substance
6:54exchange. They form the blood-brain
6:56barrier, preventing harmful substances
6:58from entering. You cannot let every
6:59substance in the blood leak into the
7:01brain, folks. This is very dangerous.
7:03Because look, that is the main control
7:05mechanism.
7:06If you damage that, you shut down the
7:08power to the whole system. So it says, "
7:11Wait a minute, I cannot recklessly pass
7:12everything you take into the blood to
7:14the brain." It says let there be a
7:15barrier here. The glia that does this is
7:17the astrocyte, young people. These must
7:19be known. Look, we have a "what if it
7:21appears" question in our book about this
7:23. Let's solve it and reinforce it.
7:26The nervous system consists of neurons
7:28and supporting cells called glial cells
7:30. Nice. Which of the statements about
7:32glial cells is incorrect, it asks? Let's
7:35review. Astrocytes synthesize myelin
7:37sheaths for neurons in the central
7:38nervous system.
7:40No, who synthesized the myelin sheath?
7:42Bravo to you. You say, "Teacher, there
7:44were Schwann and oligodendrocytes." What
7:46were astrocytes supposed to do?
7:47Blood-brain barrier. That's why number
7:49one is already wrong. I'm looking at two
7:51. Schwann cells produce myelin sheaths
7:52for peripheral nervous system neurons.
7:54Look, this is correct. Producing myelin
7:56sheaths is correct. Doing it for the
7:57peripheral nervous system is also
7:59correct. I'm looking at three.
8:00Microglial cells create and transmit
8:03impulses, it says. No, we said there is
8:05no impulse formation here. We said they
8:08are supporting cells. Wrong. Ependymal
8:10cells, I'm looking at four.
8:12Ependymal cells fight microorganisms by
8:14phagocytosis, it says, but if it says
8:15phagocytosis, what should we have said?
8:18We should have said microglia, friends.
8:20Not ependyma. What was ependyma? It was
8:23forming CSF. Since it asked for the
8:25wrong one, we only said two was correct
8:27, look. We mark our answer as one, three
8:30, and four. Are we in agreement?
8:33Now let's solve the question about task
8:35matching once more.
8:37The more questions you see, the more
8:38easily you will remember this.
8:40Again, look, it says I gave you the glia
8:43and their tasks, but which ones should
8:45be swapped?
8:46It says I swapped two of them
8:48incorrectly. Let's see. If it says
8:50oligodendrocyte, it should be myelin
8:51sheath and central nervous system. They
8:53wrote it correctly. Eh, I'm looking at
8:55two. It says astrocyte protects against
8:57microorganisms, but if we say protection
8:59, if we say defense against
9:01microorganisms, what should we say? We
9:04should have said microglia that do
9:05phagocytosis. It says astrocyte there,
9:08if you notice. Astrocyte was the
9:09blood-brain barrier. Look, they already
9:11wrote the exact opposite for microglia
9:13at the bottom. So actually, the task of
9:15the astrocyte was the blood-brain
9:17barrier, and microglia was to protect
9:19against microorganisms.
9:20Ependyma was already directly CSF. That
9:23is also correct. So, which ones should I
9:25swap?
9:26If I swap two and three, this table
9:28becomes completely correct.
9:30You are wonderful. Now we finished the
9:32glia, young people. Let's come to our
9:33actual cells. We will see the neurons in
9:36the nervous system. Nerve cells are
9:38specialized structures.
9:40Friends, there are two types of
9:41extensions in these called dendrites and
9:43axons, and they generate action
9:45potentials.
9:46Meaning they receive the incoming
9:47stimulus and transmit it.
9:50Because these are specialized cells, we
9:52give a separate name to their membrane,
9:54cytoplasm, and endoplasmic reticulum.
9:57Teacher, should we know them? You
9:58definitely should know them. Friends,
10:00the neuron membrane is called the
10:02neurolemma. Its cytoplasm is neuroplasm
10:04. Look, it resembles the end of
10:06cytoplasm.
10:07The most important, friends, is that we
10:10will call its reticulum Nissl bodies.
10:13I want you to know this. It will come up
10:15as a concept in your questions.
10:17Adult individuals generally lack the
10:19ability to divide, and all neurons,
10:21friends, contain an axon, dendrites, and
10:23a cell body.
10:25We say structures outside of this are
10:27present in some. Let's see. The shape is
10:29important for us. You will see the shape
10:31quite often. I will explain it to you
10:32from there. Then I will tell you their
10:34functions one by one. Friends, look here
10:37, the short and numerous extensions are
10:39dendrites. Since it is an eukaryotic
10:41cell in the middle, of course, I am
10:43describing a human one.
10:45Friends, the nucleus and organelles
10:47carried by the eukaryotic cell are
10:48located here, and we call the place
10:50where this is found the cell body.
10:53Continuing, the entire long extension
10:56here is an axon for us.
10:58And these parts found at the very end of
11:00this axon are referred to as axon
11:02terminals, young people. And some
11:04neurons have a myelin sheath. It does
11:07not have to be present in all of them.
11:08This myelin sheath, look, is the
11:10outermost sheath, friends.
11:13If it is peripheral and forming a myelin
11:15sheath, you can see Schwann cells, of
11:17course.
11:19But if it is central, you can see
11:21oligodendrocytes.
11:22However, where there is no myelin sheath
11:24, there are node-like gaps, if you
11:26notice.
11:27We will call these nodes Ranvier nodes,
11:29young people.
11:30So, there is no myelin sheath at the
11:32Ranvier node. We will say it is the
11:34place where the myelin sheath is
11:36interrupted, okay?
11:37Now I will state their functions one by
11:39one. Which parts might come up from
11:41where? Let me tell you the likely places
11:43that might come up.
11:45Young people, if it asks where the
11:47nucleus, organelles, or, for example,
11:49the Nissl bodies in the cell body are,
11:52you have learned that Nissl bodies are
11:54endoplasmic reticulum.
11:56What was the second thing you learned?
11:57You said, "Teacher, as in eukaryotic
11:59cells, the nucleus and organelle
12:01structures were located in this thing,
12:03the cell body." Therefore, you say it
12:05will be found there as well. We do not
12:07see a centrosome, friends. Okay? There
12:09is no centrosome structure.
12:11Those that lack it do not have the
12:12ability to divide. Because they enter a
12:14resting phase that we call G0. We say
12:17neurofibrils in the cell body are
12:19effective in impulse transmission. Then
12:21let's come to the dendrite. The dendrite
12:23is that short and numerous extension
12:25emerging from the cell body, young
12:27people. Its purpose is this. It receives
12:29stimuli and transmits them to the cell
12:31body. So, where is the stimulus actually
12:33received first? It is brought to the
12:35dendrite. From there, it proceeds to the
12:37cell body, then to the axon and axon
12:39terminal, young people. I will state
12:41that, and of course, I will not see
12:43myelin in the dendrite. Myelin is a
12:45structure I can see in the axon. What is
12:47an axon? That single and long extension
12:49emerging from the cell body.
12:51You might see myelin here, or you might
12:53not. Please pay attention. Not every
12:55neuron has to have myelin, young people
12:57. At the axon terminal, substances we
13:00call neurotransmitters are secreted.
13:02These neurotransmitters, look, I want
13:04you to underline this. It will come up.
13:07Let me show you right here.
13:09It is secreted from the axon terminal
13:10and is actually a message to stimulate
13:12the next cell.
13:14You know how we message each other? That
13:16message, friends, is this. We will call
13:18it a neurotransmitter.
13:20Then I look.
13:21The end of this sentence is very
13:23important, look.
13:24By secreting neurotransmitter substances
13:26, it carries the stimulus to another
13:28neuron or an effector.
13:29What was an effector? It was the
13:31response. It says you can come to the
13:33response or you might be stimulating
13:35another neuron.
13:36Its length can vary from a few
13:38micrometers to 1 meter. In fact, the
13:41longest axons are the sciatic nerves
13:43that go to the legs. There is even a
13:45condition called sciatic nerve
13:47compression. You may have heard of it,
13:49young folks. I want to emphasize that
13:51this is a nerve-muscle disorder, meaning
13:53it is related to the nervous system. Now
13:55, let's look at these structures in
13:57neurons, friends. What are these nodes
13:59of Ranvier? What does myelin provide? If
14:02there is no myelin, why aren't there
14:03nodes of Ranvier? Let's discuss them
14:05together. Young folks, the place we call
14:08the node of Ranvier is where the myelin
14:09sheaths are interrupted. So, there is no
14:12myelin sheath at the nodes of Ranvier.
14:14Saltatory, or jumping, conduction occurs
14:17here. I'm showing it right now. These
14:19are the places where the myelin sheath
14:20is, if you notice. And here, friends, I
14:23see an unmyelinated axon below. Above,
14:26there is a myelinated axon. Do you know
14:28what happens? Actually, the myelin
14:29sheath provides this.
14:31When an impulse is transmitted, while it
14:33is being transmitted, the node of
14:35Ranvier says this: Skip the places where
14:38I am, and carry this impulse in the
14:40places where I am not, the nodes of
14:42Ranvier.
14:43And I will explain to you in a moment
14:45what carrying this impulse means.
14:47But in an unmyelinated axon, if you
14:49notice, it makes this change at every
14:52step.
14:53So, in a myelinated one, it does this.
14:55It jumps. Look, it proceeds step by step
14:58, with big strides.
15:00But it does this at the nodes of Ranvier
15:02sections.
15:03If there is no myelin, it happens slower
15:06because it does it at every step, young
15:08folks.
15:09The whole point of the myelin sheath is
15:10providing this. Let's look right here.
15:13It is a fat and protein structure. We
15:15call this lipoprotein. It is in the
15:17structure and actually provides
15:19electrical insulation.
15:20So, by providing isolation this way, it
15:23allows our impulse to be transmitted
15:25quickly.
15:26If there is a myelin sheath, friends, we
15:29say that transmission is multiplied by
15:3110. It does not have to be found in
15:33every neuron. I remind you that if it's
15:35in the central nervous system, you will
15:37say oligodendrocyte, and if someone asks
15:39who produces it in the peripheral
15:40nervous system, you will say Schwann. I
15:42already explained and solved this for
15:44you in the very first slide. I have a
15:46previous exam question here. Let's look
15:47at that, young folks. They asked us
15:49which of the statements about the myelin
15:51sheath are correct. Very good, let's
15:53look. Impulse transmission is relatively
15:56faster in myelinated axons. Yes, because
15:58why? What was it doing there? It was
16:00providing insulation. It says it
16:01correctly. Myelin sheath on the axons of
16:03all neurons in the nervous system. No,
16:05we said it does not have to be in all of
16:07them, if you notice. There is no myelin
16:10sheath at the nodes of Ranvier on the
16:12axon. That's why it's called a node of
16:14Ranvier anyway. Since it asks me which
16:16is correct, what will I say? Except for
16:18two, I say one and three. I am marking
16:20my answer, young folks. Are we in
16:22agreement?
16:23Let's solve its twin right away, just in
16:25case you run into it.
16:27Look what it says here, friends. It asks
16:29what is incorrect regarding the myelin
16:30sheath. It has a lipoprotein structure,
16:32meaning lipid protein. It said in some
16:35neurons 'axons, it said "some," very
16:37good. For example, in the OSYM question
16:38earlier, what did it say? It said "all
16:40of them." Impulse transmission is faster
16:42in myelinated axons. Yes. It is found at
16:45the nodes of Ranvier on the axon. No.
16:47The parts where it is not found are
16:49already called the nodes of Ranvier.
16:51On the contrary, it provides electrical
16:53insulation in the axons of neurons. It
16:55speeds it up this way. Now I am coming
16:57to explain my neuron types. Friends, we
17:00are not just learning the structure.
17:01It’s not in the curriculum. Neurons may
17:03differ structurally, but we will focus
17:05on how they differ by function.
17:08In terms of function, friends, we will
17:09learn three types of neurons. We will
17:11learn them as sensory neurons,
17:13interneurons, and motor neurons. Let’s
17:15start with the sensory neuron.
17:17What is its other name? It is the
17:18afferent neuron. This one actually does
17:20the following. It detects the stimulus
17:23from the receptor, or rather, it brings
17:25the stimulus received from the receptor
17:27to the central nervous system.
17:29So, it is adjacent to the receptor. It
17:31is located in the peripheral nervous
17:32system. What do you think happens if a
17:34sensory neuron is damaged? Notice that
17:36we said this is the one that takes the
17:37stimulus and brings it to the central
17:39nervous system. Then, if its function is
17:41impaired, the stimulus cannot reach the
17:43CNS from the receptor. What is the best
17:45example of this, folks?
17:48The fact that a stimulus is not
17:49perceived at all and no impulse is
17:51generated there is local anesthesia.
17:54For instance, I won’t say "tooth dentist
17:56"—they don't like being called just "
17:57dentist." When we go to our dental
17:59doctors, our dentists, what do they do?
18:01They apply local anesthesia, right? It
18:03numbs the area. What are you actually
18:05doing there?
18:06Because it is regionally numbed, meaning
18:09your sensory neurons are numbed, you
18:10don’t feel pain while the doctor is
18:12performing the procedure.
18:14Because there is no one to take the
18:16stimulus and bring it to the central
18:18nervous system to feel pain and react.
18:20You’ve numbed that neuron. But
18:22consciousness is still there.
18:24So, since the other neurons in the
18:26central nervous system are still working
18:27—they aren't numbed—you can do it when
18:29the doctor tells you to open or close
18:31your mouth or move your tongue.
18:34Local anesthesia is a very good example
18:37of this, folks. Our second neuron is the
18:40interneuron. The interneuron is as
18:41follows. It is directly a component of
18:43the CNS. Meaning it is found in the
18:45brain and spinal cord. Its function is
18:47this. It evaluates the information
18:48brought by the sensory neuron, friends,
18:50and provides a response. So, we say the
18:53interneuron is the one that gives the
18:55response and tells you what you need to
18:57do, folks. Go ahead and guess what
18:59happens if an interneuron is damaged?
19:00Even if you receive the stimulus, you
19:02cannot react. We say the best example of
19:04this, friends, is paralysis.
19:07Even if a stimulus arrives, no response
19:09can be generated here. Because the one
19:12who evaluates it has been impaired.
19:14Finally, there is the motor neuron. What
19:16is the motor neuron? Efferent. So, the
19:18interneuron evaluated it and gave a
19:20response; this [neuron] takes that
19:22response and carries it to the effector
19:23.
19:24Meaning it brings it to your muscles or
19:26glands there so that a reaction can
19:28occur. That is why we call it the
19:31efferent neuron. We will see it in the
19:33PNS, the peripheral nervous system.
19:35Go ahead and guess what happens if a
19:37motor neuron is damaged? The sensory
19:39will bring it, the interneuron will
19:40evaluate it, but since it isn't carried
19:42to the effector, we won't be able to
19:44react. For example, Botox is the best
19:46example of this, folks. What do we do in
19:48Botox? We numb the motor neurons.
19:51Since the stimulus doesn't reach the
19:53muscles, my lines there don't form as
19:55long as I don't move my muscles.
19:57Botox with motor neurons is also a good
19:59example. Let’s continue with our
20:01inferences immediately. Neurons are
20:03given above according to their functions
20:05. Notice they gave them as sensory,
20:07interneuron, and motor. Very good. Based
20:09on this, which of the following is not
20:11expected to be found in common in all
20:13the given neurons?
20:15I will see a nucleus, eukaryotic cell,
20:17and axon terminal; I will already see
20:19dendrites and axons in all of them, but
20:21I don't necessarily have to see a myelin
20:23sheath, friends. Interneurons, by the
20:25way, already make up the majority of
20:27neurons, and we say they are myelinated
20:29. But we don't have to see it in every
20:31neuron, guys.
20:32Let's immediately look at another
20:34deduction question in our book. Then we
20:36will continue with our topic. Some
20:38definitions regarding the nervous system
20:40are given below.
20:42When these definitions are matched,
20:43which of the following is left out?
20:45A very nice concept question. If it says
20:48it is located in the central nervous
20:50system, what should I say? "Teacher,
20:51this is talking about the interneuron."
20:53I matched it. Then I look at the
20:55structure that forms a response to
20:57stimuli received from the motor neuron.
20:59If it says response, what is it directly
21:00, friends? Effector. Okay. Then, if it
21:03says it transmits the stimulus it
21:04receives from receptors to the
21:06interneuron, if it takes it from the
21:07receptor and brings it to the CNS, what
21:09is it already? It is a sensory neuron.
21:11What did it say next, guys? The
21:13specialized cell that receives stimuli
21:14from the internal and external
21:16environment is the receptor. If you
21:18notice, who was left out here? The motor
21:20neuron was left out. How could you
21:23define it? If you were to define the
21:25concept, what would you say? You would
21:27say, "Teacher, it is the one that takes
21:28the response formed in the interneuron
21:30and carries it to the effector," right?
21:31Bravo to you, guys. Its concept was
21:34already exactly that.
21:35Now I am continuing.
21:37From now on, we are moving on to a
21:39different part, friends.
21:41Impulse formation and transmission. I
21:42have used the term impulse until now,
21:44but what is an impulse? Friends, it is
21:46actually a stimulus. In other words, we
21:48call the electrical and chemical changes
21:50that a stimulus creates in a neuron a
21:52stimulus. We use the expression impulse
21:55to describe that stimulus. What can a
21:57stimulus be? It can be everything coming
21:58from the internal or external
21:59environment. There is no rule that a
22:00stimulus must come from the outside. And
22:02the terms threshold value and action
22:04potential are important. Guys, the
22:06threshold value is this. It is the
22:07lowest stimulus intensity that enables
22:09the formation of an impulse in neurons.
22:12And the action potential is the
22:14electrical change that the impulse
22:16creates in neurons, guys.
22:19We will talk about a concept here
22:20immediately. It is also in our book, of
22:23course. I will talk about the
22:24all-or-none principle.
22:26Friends, it is a nerve fiber's giving a
22:29maximum response to all stimuli at and
22:31above the threshold value, while not
22:34responding at all to those remaining
22:36below the threshold value.
22:39So it says all or nothing. It says, if
22:41my threshold value is here, I don't care
22:43how much you exceed the threshold value
22:45. Since I respond with maximum power the
22:47moment you reach the threshold value, it
22:49says it doesn't change anything for me
22:51whether you exceed it by this much or
22:53this much. It says, the moment you reach
22:55here, I am already transmitting it with
22:56all my strength. But it says if you stay
22:58below, I don't respond at all. That is
23:01what we call the all-or-none principle,
23:03guys.
23:04When shown in questions and figures, it
23:06is shown like this. It represents a
23:08nerve fiber.
23:09Note the intensity of the stimulus; up
23:11to here, look, I see no response. There
23:14is a response here. So the threshold
23:15value is here, friends, and I say that
23:17the moment it reached the threshold
23:19value, it gave the maximum response.
23:21You can exceed the threshold value as
23:22much as you want.
23:23Even if you exceed it, your response
23:25here does not change. The action
23:27potential continues in the same way.
23:29Stimulus intensity, frequency, and
23:31quantity. The stimulus arrived. You
23:34brought me a stimulus.
23:36Even if its intensity, frequency—that is
23:38, its rate—or its quantity increases,
23:41the impulse speed does not change.
23:43Why?
23:44Because the ATP required for the impulse
23:47speed is produced by the neuron itself.
23:51Since the ATP is not obtained from the
23:53incoming stimulus, the incoming stimulus
23:55has more intensity. It has a higher
23:58frequency. It is in greater numbers.
24:00This does not mean more ATP. ATP does
24:04not pass from cell to cell. So, I came
24:06and tapped you like this, or I came and
24:08punched you. Here, the stimulus
24:10intensity changed. But here, friends,
24:12the speed of the impulse does not change
24:14depending on this. Because the ATP
24:16necessary for that speed is produced
24:18within the neuron itself. It is not a
24:20situation related to the incoming
24:22stimulus. In other words, it is not a
24:23situation related to me. It is a
24:24situation related to you. Therefore,
24:25regarding the "all-or-none" principle,
24:27friends, what we need to know is the
24:28opposite—well, let's not say opposite,
24:30but a different phenomenon, friends—is
24:32the staircase effect. The staircase
24:34effect explains this.
24:36A nerve bundle, a nerve cord consisting
24:38of many nerve fibers.
24:40If you notice here, in the "all-or-none
24:41" principle, we always said a single
24:43nerve fiber.
24:44Look, I'll show you here in the concept
24:46, we said a single nerve fiber, but now
24:48it says what happens if there are many
24:51nerve fibers?
24:52Since their threshold values will be
24:54different from each other, friends, the
24:55"all-or-none" principle does not exist
24:57here. There is a staircase effect here.
25:00Meaning, as you increase the stimulus
25:01intensity, the number of nerve fibers
25:03stimulated also increases, so the
25:04response intensity also increases.
25:07We call the increase in the nerve
25:09bundle's response depending on the
25:10increase in stimulus intensity until all
25:13nerve fibers are stimulated the "
25:14staircase effect."
25:17So, look, there is more than one nerve
25:18fiber here.
25:20We will call these a nerve bundle,
25:21friends.
25:22It says you don't see the "all-or-none"
25:25principle here. Why? Because it says
25:27their threshold values can be different
25:29.
25:30For example, it says when you send this
25:32or this, one can be stimulated, but when
25:34you send this, when you increase the
25:36intensity, since more than one nerve
25:38fiber will be stimulated, the given
25:40response also changes.
25:41It says this is called the staircase
25:43effect. Why? On a staircase, look, the
25:45threshold height of each step is
25:47different.
25:48That's where the name comes from. I will
25:50solve my question as soon as one comes
25:52up. I want to reinforce this part.
25:54The responses to stimuli of different
25:57intensities given to a human neuron are
25:59shown. I pay attention that it says "a
26:01neuron." I catch it in the question. You
26:03will catch it too. Pay attention. I have
26:05one neuron. The "all-or-none" principle
26:08is valid.
26:09So, when it asks what cannot be said,
26:11for a neuron, you cannot say it only
26:13responds to stimuli above the threshold
26:15value, only threshold value...You must
26:17say including the threshold value.
26:20You need to say threshold value and
26:22above. If you say only above, I won't
26:24accept that.
26:26As the stimulus intensity increases, the
26:28impulse speed in the neuron also
26:29increases. The ATP required for speed is
26:31not taken from the stimulus. I say your
26:33intensity does not affect my speed, and
26:35I look at the third one. As the stimulus
26:37intensity increases, the response
26:38intensity in the neuron does not change
26:40. Why? I see a single nerve fiber. The "
26:42all-or-none" principle is valid. It says
26:44it correctly. Since it asks what cannot
26:47be said, youngsters, we say one and two
26:49, okay? Now let's come to my other
26:51question. It will be related to this
26:53again, but what is here? Also, there is
26:55a staircase effect if you pay attention
26:57. In the graphs below, you see the
27:00response to increasing stimulus
27:02intensity in a single neuron and a nerve
27:04bundle; look, it says one neuron and the
27:06nerve bundle here. There are responses
27:08that take place. It asks what is correct
27:11according to the graphs. I am looking at
27:13number one. The staircase effect is
27:14observed in the nerve bundle. Because it
27:16mentions the nerve bundle, yes, there is
27:18more than one threshold value, meaning
27:20staircase steps. It states it correctly
27:21. I am looking at number two. In a
27:23single neuron, all stimuli at or above
27:25the threshold value are responded to
27:26with the same intensity. That is exactly
27:29the definition of all-or-none anyway. I
27:31am looking at number three. The reason
27:32for the increase in response intensity
27:34in the staircase effect is that the
27:35neurons have different impulse speeds.
27:38No, a neuron's speed continues just as
27:40it started.
27:41Here, the stimulated nerve fiber changes
27:44. It said it in reverse; it stated
27:45something different in the background.
27:47Therefore, since it asks for the correct
27:49one, our answer is one and two.
27:52You are great, youngsters. Now I will
27:54mention two final different events in my
27:57topic section.
27:59One is how these stimuli travel. In
28:01other words, I will explain the
28:02possibilities of the impulse to you. I
28:04will explain both the electrical and
28:05chemical aspects. Then I will finish by
28:07solving my questions. If you are ready,
28:09let's begin. We will call it impulse
28:11transmission in neurons, friends.
28:14Now, polarization, depolarization, and
28:16repolarization are not explained in as
28:18much detail in the curriculum as they
28:20used to be, friends.
28:23But I will still give you some tips here
28:25as concepts so there is no disconnect.
28:29So that you don't have to memorize
28:30anything in one place.
28:32Friends, this explains this to us: it
28:34says when you look at a neuron, you are
28:37ultimately looking at a cell.
28:39The cell has an inside and an outside.
28:41Focus only on the place I am explaining
28:43right now. Do not watch left and right
28:45and try to read those places. Look here
28:47. This is the inside of the cell. Okay?
28:49This is the outside of the cell. These
28:52represent the cell membrane.
28:54It says to me, first, you need to know
28:56this here.
28:58The inside, friends, is normally, as
29:00long as no stimulus arrives—that is, in
29:03the resting state, which we will call
29:05this resting state polarization, friends
29:08.
29:09The inside of the cell is negatively
29:11charged. The reason for this is that
29:13there are many ions inside.
29:15The outside, however, is positively
29:16charged.
29:17We will also mention two ions. Because
29:20these are what provide the impulse in
29:21the nervous system. Who are the two
29:23friends? Sodium and potassium.
29:26What is always abundant inside, look,
29:28what color should I show it with?
29:31Let me show it with purple or blue. If
29:33it is not visible, let your brother
29:35Murat warn us.
29:36What should we say about the inside,
29:37friends? Teacher, potassium is abundant
29:40inside. I call them kings. Kings are
29:43inside, ingrates are abundant outside.
29:45Meaning, sodium is also abundant outside
29:47. Both of these have a positive charge,
29:49though. Okay? Sodium is more abundant
29:52outside. For example, 80%of it is
29:54outside, 20%is inside.
29:56For potassium, it is just the opposite:
29:5980%inside, 20%outside.
30:01When it is like this, we call it the
30:03cell's resting state.
30:04In fact, resting is polarization, so let
30:07it come to your mind from the P of
30:08polarization.
30:10Parking state. Parking of cars. In other
30:12words, the place where they rest. I want
30:14you to encode it directly from here.
30:16Okay?
30:18Now, there is an event here.
30:21Even though it is called resting, it is
30:23not that easy for a cell to maintain its
30:25vitality, friends.
30:27In return, it will expend energy.
30:29Meaning, it will spend ATP, guys. Or
30:31rather, it will spend the energy
30:33released from ATP. Now, look at the
30:35figure here. I have the cell membrane,
30:37good. It shows the inside of the cell.
30:39It shows the outside of the cell. I am
30:41looking.
30:42Friends, when I look inside the cell,
30:44notice what is here?
30:46It shows channels. But, what charge will
30:49I see in excess here, guys?
30:52Mostly inside, meaning during the
30:53resting state, there should be more
30:55negative charges.
30:57Outside, there should be more positives
30:59, and the most important thing in this
31:02process is this.
31:03An expression we call the
31:05sodium-potassium pump. I would like to
31:07ask you to draw this. Let's draw it
31:10together, friends.
31:11Look, where is it mentioned here? I want
31:13to find the first expression right away
31:15.
31:16Sodium-potassium pump. Yeah. Look, I
31:19want you to draw this.
31:21If you see this definition somewhere,
31:23when it says sodium-potassium pump, this
31:25is what it means.
31:29Now, normally, if you notice, both
31:30sodium and potassium are small, and
31:31according to diffusion rules, they want
31:33to equalize inside and outside the cell
31:34.
31:36They want to be 50-50.
31:39But our sodium-potassium pump located in
31:42this cell membrane acts like an officer
31:45, a customs officer, and says, "Friends
31:47, sodium will be found more outside," it
31:50says.
31:52It prevents them from passing inside.
31:54"Potassium will stay inside, it won't
31:56escape outside," it says. And since you
31:58are employing customs officers, what
32:00will you pay the officer? Salary. So,
32:02what is your salary here? ATP. We expend
32:05energy during the resting state. We
32:07spend ATP during the resting state.
32:09Because this has a cost. Normally, these
32:12are small structures, look. They
32:13equalize according to diffusion rules.
32:1550%sodium, 50%sodium would be equal
32:17inside and outside the cell. Potassium
32:19is the same.
32:20But because you are defying diffusion
32:23rules here, using active transport to
32:26throw sodium out and imprison potassium
32:29inside, ATP is spent here.
32:32We say vitality is essential, guys. Okay
32:34? This was the most important part here
32:36. Now I come to receiving the stimulus.
32:39So, my arm was in a resting state like
32:41this, for example. You came, you touched
32:43me. Now, what is happening in my cell?
32:45How does it perceive it? How does it
32:46perceive the touch?
32:48Friends, we call the disruption of
32:50polarization here depolarization.
32:53You know "de" is our negative prefix,
32:54when it comes to the beginning of a word
32:56, look, it says I disrupted the
32:57polarization.
32:58Do you know how it disrupts it, guys?
33:01When the impulse arrives at the cell
33:03inside, we take the customs officers on
33:05break in turn.
33:08And the friends who always go on break
33:10first are the sodium officers. The
33:12sodium gate opens. The officer goes on
33:14break and sodium moves according to
33:16diffusion rules. What was diffusion?
33:18Diffusion from high to low concentration
33:20. So, where was the sodium abundant from
33:22the very beginning, you ungrateful ones
33:24? Sir, it was outside. Bravo to you.
33:26Then, when the officer opens the gate,
33:28what will sodium do? It will escape
33:30towards the inside of the cell, guys,
33:32look. Since it is positively charged
33:34itself, what is it doing inside? It is
33:36letting in positive charges, and the
33:37inside becomes positively charged.
33:40And since the outside lost the positive
33:42charge, it becomes more negatively
33:43charged in terms of weight.
33:45And since it passes through the channel
33:47from high to low concentration, it moves
33:49according to diffusion rules and ATP is
33:51not spent. We call this depolarization.
33:55Then there is the exact opposite of this
33:56, repolarization. What was "re"?
33:59Repolarization, the R stands for
34:01reversing, friends.
34:02You know how cars have R for reverse.
34:04Let me even show you right here.
34:07What does D stand for in a car's gear?
34:09It stands for drive, right? In
34:11depolarization, the impulse is actually
34:13being transmitted forward. In
34:14repolarization, it's coming back. It is
34:17trying to return to its original state.
34:19Why is it returning to its original
34:20state? Wait, did the slide close or
34:21something?
34:22Oh.
34:23Let's fix it like this. There we go.
34:25In repolarization, guys, it returns to
34:26the original state.
34:28The R meaning comes from there. So
34:30teacher, what is happening here? What is
34:32happening here is this, guys.
34:34You know how the first of our customs
34:36officers, sodium, had gone on a break?
34:38Potassium says, "Wait a minute, what
34:40about me?""I want to go on a break, too
34:42," it says.
34:43This time, friends, the potassium gates
34:46open.
34:47Potassium gates open, and our kings were
34:49inside from the very beginning. This
34:51time, they are escaping outside.
34:53Potassium transport outside the cell
34:55begins, friends. Of course, since it's
34:57from high to low, it passes by diffusion
34:58. No ATP is consumed. This is also
35:00positively charged. Naturally, the
35:02outside becomes positive again, and the
35:03inside becomes negative again.
35:05In terms of positive and negative,
35:07repolarization is actually the same as
35:09polarization at the beginning.
35:12But even if the charges are the same as
35:14with sodium-potassium, the ions, sodium
35:16and potassium, are in the exact opposite
35:18places.
35:20And here, guys, at the very beginning it
35:21happens through diffusion, but do you
35:23know what happens at the end of
35:24repolarization?
35:26Our customs officers finish their breaks
35:29and return to their posts.
35:32That is, the sodium-potassium pump
35:34reactivates, guys, and since it is
35:37active, the cell takes the kings back in
35:40and kicks the ingrates out, just like in
35:43the beginning.
35:46The inside becomes negative again, and
35:48the outside becomes positive again. Why
35:50does the cell do this? The best question
35:53here, which is already in your book as a
35:55note, I'll say it again.
35:57Friends, if you don't return a cell to
35:59its original state and leave it there,
36:01it cannot detect the next stimulus.
36:04Detecting a stimulus means, look,
36:06disrupting that original state. Meaning
36:09, disrupting the polarized state. If you
36:12don't disrupt the polarized state, how
36:14would the cell know it received a
36:16stimulus? Does it have eyes and ears? It
36:18cannot know.
36:20That's why it says you must return it to
36:22the original state so it can detect an
36:24incoming stimulus.
36:26Look, there are notes now, this part is
36:28very important.
36:30When the cell is repolarized, it cannot
36:32detect a second stimulus because the
36:34sodium channels are inactive.
36:37Because where did you leave the sodium
36:39channels open? What was the first one to
36:41open? It was the sodium officer in
36:43repolarization.
36:45For an impulse to form again, the inside
36:47of the cell must become full of kings
36:49again, and the outside full of ingrates
36:51—in other words, it must return to its
36:53original state.
36:56In this case, the sodium-potassium pump
36:57kicks in and brings the ion
36:58concentrations inside and outside the
37:00cell back to the state of polarization.
37:04When asked why, you say, "Teacher, it
37:06needs to be able to receive the next
37:07stimulus again, like we say,' leave it
37:09as you found it, 'it needs to leave it
37:11as it was."
37:13Let me give you this mnemonic right here
37:14. What did we say? Think of polarization
37:17as cars parked.
37:19Depolarization is D for drive in a car,
37:21and repolarization is reversing, doing
37:24an R, friends.
37:25It means the stimulus has caused the
37:27cell to return to its original state.
37:29Let me show you this as an animation
37:32right now.
37:33Look, it can also come in this graph
37:35format. Please don't be afraid. This is
37:37the graphic version of that shape. If
37:38you pay attention, it says membrane
37:40potential. I read the horizontal and
37:41vertical columns of my graph based on
37:43time. What's there? Did you notice it's
37:45at the minus sign? Why? Because what had
37:47I told you the inside of the cell is
37:48charged with at the very beginning? It
37:50is negatively charged because anions are
37:52more abundant. See, did you see that?
37:53That's the reason it says minus 70.
37:55It starts with a minus, friends. A
37:57stimulus arrives. As the stimulus
37:59arrives, what would it be charged with
38:01inside? It's a plus because sodium will
38:02escape inside. If you pay attention,
38:04look, how did it slowly move from minus
38:06? It switched to plus. Then, in
38:08repolarization, what will happen again,
38:10guys?
38:11It will be negatively charged again here
38:13.
38:13If it goes to a more negative state,
38:15that can be called hyperpolarization. It
38:18means becoming more negative compared to
38:19the start. Here, friends, it is enough
38:22for me if you know these three events
38:24this way. There's no need for too much
38:26detail, but it's important to know this
38:27. When we say sodium-potassium pump,
38:30there is opposition to diffusion. In
38:32other words, spending ATP, there is
38:33active transport. But sodium passes
38:35alone from high to low concentration.
38:37Potassium passes alone from high to low
38:38concentration. These are diffusion. ATP
38:40is not spent on this. You have to know
38:43and interpret these. So you are
38:44responsible for this much. Are we agreed
38:46? Now I am coming, guys.
38:48To the notes on factors affecting
38:50impulse speed.
38:52These are very confusing. That's why a
38:54lot of questions come from here. We will
38:55pay attention. Let's take a look
38:56immediately.
38:58Among the factors affecting impulse
38:59speed, one, friends, is that if there is
39:01a myelin sheath, we already say it's on
39:02average times 10.
39:04Meaning, where there is a myelin sheath
39:06, it's faster than where there isn't.
39:07Next is axon diameter. You know in
39:09physics, when the diameter increases,
39:11the resistance decreases and speed
39:12increases. Same logic. As the diameter
39:14increases, this also affects it
39:15positively. Here, resistance will
39:17decrease, speed will increase. These,
39:18friends, increase the impulse speed.
39:20Temperature increases it up to the
39:22optimum level.
39:24Optimum is the best speed, but if you
39:26take the temperature and decide to raise
39:28it to 50s, you kill the lipoprotein
39:30structure and the cell.
39:31You kill the proteins and its enzymes.
39:33That's why you need to know it's optimum
39:35. The note on the side is very important
39:37. Factors affecting the number of
39:39impulses. Look, speed on one side,
39:40number on the other. Speed and number
39:42are not the same thing. Please do not
39:44confuse these. These will come up. They
39:47will come as trap questions. Friends, if
39:49the frequency, intensity, or duration of
39:52the incoming stimulus increases, the
39:54number of impulses naturally increases.
39:56The staircase effect comes into play,
39:58but that doesn't mean it increases the
39:59speed. Why? Because the ATP required for
40:02speed comes from the neuron itself. It
40:04has no connection with the incoming
40:05stimulus. We don't care about the
40:07stimulus one bit there.
40:09So you will know that this explains
40:11speed and this explains the number. You
40:14will not confuse them. I will solve my
40:16questions about this right away.
40:18Friends, it said which of the quantities
40:20increasing causes an increase in impulse
40:22speed?
40:23I'm looking, teacher, if the axon
40:24diameter increases, it increases it.
40:25Saying I don't care about the stimulus
40:27one bit, you mark the answer as Adana.
40:30Then I look at my other question
40:31immediately and will continue with my
40:33topic.
40:35Friends, Şule said I did a study on
40:37impulse transmission in neurons.
40:39Here, it says Şule did something wrong.
40:41We will find it. Let's see. Impulse
40:44transmission does not occur in polarized
40:47neurons. We called this the resting
40:49state. She is saying it correctly.
40:51In 2, it says, during depolarization,
40:53the cell interior is positive and the
40:55exterior is negative. Yes, that is what
40:57being depolarized means. Because
40:59initially, when polarized, the inside
41:00was negative.
41:02Why does the inside become positive
41:03during depolarization? Because you say
41:05sodium ions are rushing inside. Good for
41:07you. In 3, Şule says, the energy
41:08required during impulse transmission is
41:10provided by the stimulus. No, Şule got
41:12that wrong here. She should have said it
41:14comes from the neuron itself. What did
41:17Şule say in 4? Impulse transmission is
41:18faster in myelinated neurons. Correct.
41:20Myelinated neurons have nodes of Ranvier
41:22. And why? If you look at myelinated
41:25neurons, friends, the areas without
41:26myelin are called nodes of Ranvier. I
41:28mean, if there is no myelin, what would
41:29you even call a node of Ranvier? So, she
41:31said that correctly. Our answer is
41:33Ceyhan. Now, young people, we have made
41:36great progress so far. We have reached
41:38the final part of the subject. What are
41:40we going to talk about? We will talk
41:41about impulse transmission at synapses.
41:43What does this mean? What does impulse
41:45transmission at synapses mean?
41:46Friends, look, what we have actually
41:48learned up to this point about polarized
41:50, depolarized, and repolarized states,
41:52look here, young people.
41:53Let these represent my dendrites. Okay?
41:56Let me quickly draw a crude axon for you
41:58.
41:59Let these be the ends of my axon.
42:01I want you to imagine the next neuron.
42:04Well, it doesn't have to be a neuron, it
42:05could be an effector, it doesn't matter
42:07.
42:07Still, I will draw a neuron for you. We
42:10drew it like this, okay?
42:12Now it says, look, here in polarization
42:14, depolarization, and repolarization,
42:16what did the transmission actually do?
42:19It traveled from the dendrite toward the
42:21axon terminal.
42:22And because you performed a plus-minus
42:24exchange here, this event was electrical
42:26. But it also says you spent ATP. You
42:29performed active transport. Cellular
42:30respiration continued. Look, I am
42:32telling you something very important.
42:33Listen to this now, don't look around,
42:34take your notes.
42:36When you consider all three—polarized,
42:38depolarized, and repolarized—didn't I
42:40perform a plus-minus ion exchange?
42:42I did. This event is electrical. But
42:44didn't I spend ATP when I came back? I
42:46did; I performed active transport.
42:48So, where does this ATP come from for me
42:49? From cellular respiration. Bravo to
42:51you. You see, you learned the topic in
42:5312th grade, you know it. What is
42:54cellular respiration? It is the
42:56breakdown of nutrients with oxygen in
42:57the mitochondria for our cells. Bravo to
42:59you. Why? Because it is the one that
43:01produces ATP. Therefore, you are
43:02actually increasing cellular respiration
43:04here as well, and since this is chemical
43:06, what you call cellular respiration is
43:08a series of chemical reactions.
43:11Here, friends, in PDR—that is,
43:13polarization, depolarization, and
43:15repolarization—the stimulus is both
43:17electrical and chemical.
43:20So we say it is electrochemical.
43:23Now, we will learn this.
43:25Synaptic transmission, that is, how the
43:28impulse is transferred from the axon
43:30terminal of one neuron to the dendrite
43:32of the next. Because PDR taught me this
43:35. How do I go from the dendrite to the
43:37axon terminal in a single neuron?
43:40It taught me that. It mentioned myelin,
43:42axon, Ranvier, and how it progressed
43:44through there.
43:45But why, because how was the stimulus
43:46received? It goes in the order of
43:48dendrite, cell body, axon, and axon
43:49terminal. But now, what will happen?
43:53Here, friends, when we look at the
43:55impulse between two neurons or between a
43:58neuron and effectors, we call this gap
44:00the synaptic cleft, and synaptic
44:02transmission will explain this to us.
44:05Therefore, in synaptic transmission, the
44:07direction of transmission is from the
44:08axon terminal toward the dendrite. Look
44:10, it's the exact opposite. If the
44:11question says "in a neuron," you must
44:13read the question carefully. Don't solve
44:15it while half-asleep.
44:16If it says "in a neuron," the direction
44:18of the impulse goes as dendrite, cell
44:20body, axon, and axon terminal.
44:22But if it says "at the synapse," it goes
44:24from the axon terminal to the dendrite.
44:26So, there is an exactly opposite
44:28situation. You will pay attention to
44:29this. Now, I am continuing with this
44:32part.
44:33The connection a nerve cell makes with
44:35another nerve cell or a target organ is
44:36the synaptic connection.
44:38In synapses, transmission is from the
44:40axon to the dendrite.
44:42Pay attention, and here, friends,
44:44transmission occurs via chemical
44:45substances called neurotransmitters, and
44:48bravo to you.
44:49Teacher, is this place chemical, then?
44:51Exactly so, young ones. It is chemical.
44:54I will give you examples of
44:55neurotransmitters; you must know them.
44:57Acetylcholine, serotonin, dopamine,
44:59noradrenaline, and histamine are among
45:01the best-known neurotransmitters.
45:04Because this event is chemical, it is
45:06slower than the electrical one. Because
45:09chemical reactions are always slower.
45:12In synaptic regions, the neuron sending
45:13the information is presynaptic— "pre"
45:15means before something—and the one
45:16receiving the information is
45:17postsynaptic— "post" means after.
45:20So, that is what it means, and naturally
45:22, we will call the neuron that comes
45:23later, meaning the one receiving the
45:25impulse, the postsynaptic neuron. The
45:27one sending the impulse is the
45:28presynaptic one, okay?
45:30Uh, the presynaptic neuron, and the one
45:31receiving it is the postsynaptic one.
45:33The sequence goes like this. The
45:34receptor is already a receiver; it
45:35starts with that at the very beginning.
45:37It brought it to the sensory neuron,
45:39then my interneuron evaluated it, gave
45:40an answer, and the motor neuron
45:42transferred this to my effector.
45:44The sequence continues exactly like this
45:47, but impulse transmission in synapses
45:49is a series of chemical processes.
45:52I will explain this to you first in
45:53sub-items, and then I will explain it
45:55with an animation.
45:57Why? Because in places where these types
45:59of event chains occur, the Ministry of
46:00Education likes this, and the exam board
46:02likes this.
46:03They give them mixed up and tell me to
46:05put them in order.
46:06They ask how the realization process
46:07occurs.
46:08So, if you are ready, let's go step by
46:10step; don't be afraid at all.
46:12There is nothing you need to memorize. I
46:13will already explain the logic of it to
46:14you.
46:16Look now, when an action potential
46:17depolarizes the synaptic terminals, it
46:19says that calcium enters the cell.
46:22So, what the sentence is trying to say
46:24up to here is this. It seems very long
46:26and meaningless to you.
46:28Friends, it says that when the impulse
46:30reaches the axon terminal, it means it
46:32arrives at the axon terminal.
46:34I could also write this sentence like
46:35this. When the impulse arrives at the
46:38axon terminal, calcium entry into the
46:40cell begins.
46:41Why calcium? Where did calcium come from
46:43, teacher? Bravo, a very good question.
46:45Friends, calcium is our secondary
46:47messenger in cells. So, think of it this
46:50way. I am going to make an announcement
46:52to the class, but I don't go to the
46:53class myself; I call the class
46:54representative, the president.
46:56The teacher tells the president, saying
46:57announce this, this, and this to the
46:59class.
46:59The president goes and makes the
47:00announcement in the class on behalf of
47:01the teacher. That is calcium, the
47:03president. Meaning, the secondary
47:05messenger. Think of it like the second
47:06person carrying the message.
47:08We are coming to what message is carried
47:09by the effect of calcium?
47:11When calcium enters inside, friends,
47:13there are synaptic vesicles located in
47:15the axon terminal.
47:17We call these synaptic vesicles.
47:19The synaptic vesicles open up, guys. I
47:22mean, they open themselves; this is what
47:23it means to fuse with the neuron
47:25membrane. The reason it opens is this.
47:28Inside these synaptic vesicles, there
47:30are already neurotransmitters.
47:33And these neurotransmitters, guys, are
47:35secreted into the synaptic cleft.
47:38Since neurotransmitters are large
47:40molecules, this method is called
47:42exocytosis. Why? Let’s recall from our
47:45basic biology studies. What was "exo"?
47:47To throw outside. Exocytosis means I am
47:49throwing something large out of the cell
47:51. This is important.
47:52Then, friends, these spread in the gap
47:55by diffusion. Why did it turn into
47:56diffusion? Well, you are in the gap.
47:59When outside the cell, there is no ATP
48:01for active transport or exocytosis.
48:03Naturally, it will be diffusion,
48:04logically speaking. It reaches the
48:06postsynaptic neuron or the receptor of
48:08the effector cell, it says. We called
48:11the one sending the stimulus presynaptic
48:13. What will we call the one receiving
48:14the stimulus, friends? Postsynaptic. It
48:16says this could be a neuron or an
48:18effector. But it will bind to its
48:21receptor. Do you know what happens when
48:23it binds to its receptor, guys?
48:24That cell now becomes depolarized; it is
48:27stimulated.
48:29Meaning, the sodium customs officer goes
48:31on break, and since sodium ions move
48:33into the cell, that cell becomes
48:35depolarized.
48:37And guys, after the transmission occurs
48:39, that synaptic cleft is cleaned.
48:42Meaning, those stimuli, these
48:44neurotransmitters, are broken down by
48:46enzymes. Do you know the reason for this
48:48? They are either erased or taken back,
48:50guys. The reason is this.
48:53It says if you don't clean the area, if
48:55the neurotransmitters remain in that gap
48:56, you would keep reacting as if the
48:58stimulus were still there, even after it
49:00ends.
49:01And it makes me waste ATP, waste energy
49:03, for no reason. Plus, it says there is
49:05no stimulus present. What are you
49:07reacting to? Also, it says we wouldn't
49:09be able to perceive the next incoming
49:10stimulus either. It’s the same logic as
49:12our repolarization, guys. They are
49:14cleaning the area. This is the logic of
49:16this event. Now I have explained it to
49:17you step by step. I will also show you
49:19in an animation. The stimulus arrived at
49:21the axon terminal. Calcium entered
49:22inside. The vesicles opened.
49:24Neurotransmitters were secreted. When it
49:26bound to the receptor of the neighbor
49:28cell you want to stimulate, its sodium
49:30channels opened and it was stimulated.
49:32That’s the whole thing. I am explaining
49:34it again.
49:35I am at the axon terminal. These axon
49:36terminals that send the stimulus look
49:38like a fist. That’s why it is drawn like
49:40that, in the shape of a fist. Since the
49:42one in front is sending the stimulus,
49:43what should I call it, friends?
49:45Presynaptic. The one receiving the
49:47stimulus is postsynaptic. This has
49:49receptors on its cell membrane.
49:50Receivers, just like in every cell. This
49:52one had them too. It arrived at its axon
49:54terminal. At the axon terminal, these
49:56are the synaptic vesicles. Look, if you
49:58pay attention, they have
49:59neurotransmitters inside them.
50:01When the stimulus reaches the axon
50:03terminal, calcium will enter. Look, the
50:06yellow ones are calcium. The vesicles
50:07opened.
50:09It secreted neurotransmitters via
50:10exocytosis, but they spread by diffusion
50:12in this gap, and when they bind to the
50:14receptor, since the sodium gate of this
50:16one opens, my next postsynaptic neuron
50:18gets stimulated.
50:20Meaning, it has become depolarized. That
50:22is the whole thing, guys, okay? You are
50:24wonderful. Look, it is showing me again
50:26.
50:27The function of neurotransmitter
50:29substances is specific to the cell. Not
50:30every chemical messenger stimulates
50:32every cell.
50:33In other words, every impulse that comes
50:35to the axon terminal does not have to
50:37pass to the other neuron. We call this
50:39selective resistance, friends.
50:41Here, if the neurotransmitter secreted
50:43from the axon terminal prevents passage
50:45to the other neuron, it is called an
50:46inhibitory synapse; if it allows passage
50:48, it is called a facilitatory synapse.
50:51The logic behind this is as follows. The
50:52logic behind selective resistance is
50:53this.
50:54It says each neuron should not react to
50:56everything for no reason and make us
50:57spend energy in vain.
50:59It says we shouldn't exhaust ourselves
51:01trying to produce that energy for
51:02nothing. Meaning, if a needle pricks my
51:04hand, I should withdraw my hand. I don't
51:06need to withdraw my foot or my whole
51:07body at the same time. It says don't
51:09make me spend energy in vain. That is
51:10what selective resistance is all about.
51:12So, every neurotransmitter does not
51:14necessarily have to go and bind to every
51:16subsequent post-synaptic neuron.
51:18It doesn't have to stimulate that
51:20receptor, guys. Are we in agreement? You
51:22are great. I have a past exam question
51:24right away. I have an ÖSYM twin question
51:25. After that, the topic is already
51:26finished. We are moving on to the tests
51:28. Friends, I am looking.
51:30In the nervous system, ÖSYM said impulse
51:32transmission from one neuron to another
51:34, meaning it's talking about synaptic
51:36transmission.
51:38What is wrong? In Adana, it said impulse
51:40transmission occurs in connection
51:41regions called synapses.
51:43It actually tried not to say synapse
51:45above to ask its name in Adana. It is
51:47stating correctly. I am looking at Bursa
51:49. Neurotransmitter release from the axon
51:51terminal to the synaptic cleft occurs
51:52via exocytosis. Correct. Because a
51:54neurotransmitter is a large molecule,
51:56and if you are secreting a large
51:57molecule out of the cell, you spend
51:59energy. We used to call this exocytosis
52:01, remember from TYT.
52:02I am looking at C. Receptors on the
52:04other neuron also play a role in the
52:05realization of impulse transmission. If
52:07it cannot bind to the receptor on the
52:08other neuron, the impulse won't be
52:09transferred anyway. It remains in the
52:11gap. The impulse does not pass beyond
52:12that.
52:13I am looking at D. Every impulse that
52:15reaches the axon terminal passes to the
52:16other neuron. No. There is selective
52:18resistance. If you say "every," it would
52:20be incorrect. Some pass, some are
52:22blocked.
52:23I am looking at E. When impulse
52:24transmission is completed,
52:26neurotransmitters can be broken down by
52:28enzymes and removed so that an incoming
52:29signal can be perceived. And so it
52:31doesn't pester us for nothing after the
52:33signal ends.
52:35I will solve a twin of it immediately.
52:37In case you come across it.
52:39Regarding transmission in human synapses
52:41, Adana said from the axon terminal of
52:43one neuron to the dendrite of the other
52:45neuron. Look, it's the exact opposite.
52:47If it said a single neuron, I would say
52:48dendrite to axon. Adana is correct. I am
52:50looking at Bursa. Neurotransmitter
52:52substances secreted from the axon
52:53terminal via exocytosis spread into the
52:55synapse by diffusion. Because a synapse
52:57is a gap, and you cannot see ATP there.
53:00Naturally, it will spread by diffusion.
53:02I am looking at C. It is slower than the
53:04transmission occurring along the axon of
53:05a neuron. Meaning, what it calls along
53:07the neuron's axon is talking about
53:08polarization, depolarization, and
53:10repolarization. It is stating correctly
53:11. Why is it slower? Because it is
53:13chemical.
53:14I am looking at D. Neurotransmitter
53:16substances in the synaptic gap always
53:18bind to receptors on the dendrite of the
53:21other neuron. They don't always bind.
53:23There is something called selective
53:25resistance.
53:26I am looking at E. It says when
53:27transmission is completed,
53:29neurotransmitter substances are broken
53:31down by enzymes or reabsorbed. It is
53:33stating correctly, guys. This is also
53:34correct. We say this because it needs to
53:36do some cleaning. Now we have finished
53:38our topic, guys. I will solve the
53:40questions located right behind it in our
53:42book. I will solve the test so that you
53:44learn the structure, function, and task
53:45of the nervous system. This part is
53:47important. If you are ready, let's start
53:49with our first question right away.
53:51Guys, number 1. The question says that
53:53below are two neurons with equal lengths
53:55and axon diameters. So, the length is
53:57the same, it says diameter length. That
53:59is, the axon length, but it says the
54:00axon diameter is also the same. Good,
54:02but what is the difference? If you
54:04notice, I see a myelin sheath in neuron
54:06A. In neuron B, however, this is absent
54:07. Then it asked which of the features in
54:10these neurons, in neurons A and B, are
54:12definitely the same. Our impulse
54:14transmission will be different, young
54:15people. Why? Because the one with the
54:18myelin sheath will transmit faster.
54:20Therefore, we will say this is not the
54:21same. It asks me for what is definitely
54:23the same. The target organ it stimulates
54:25. Now, how would I know for sure if this
54:27is the same? Maybe it's different. But
54:29the direction of impulse transmission is
54:30the same because it gives a single
54:32neuron. In all of them, it will go in
54:34the form of dendrite, cell body, axon,
54:36and axon terminal.
54:37Since it says "definitely," friends, my
54:39answer is only 3. Alright? Let me turn
54:41this to red, wait. There. Red shows up
54:43more clearly. Now I am coming, young
54:45people, to my 2nd. question. What is in
54:47my 2nd. question? On a nerve fiber. Look
54:49, I caught it here. Since it says nerve
54:51fiber, what will I say? Teacher, there
54:53is the all-or-none principle. Below, the
54:55axon potential of a nerve fiber is shown
54:58. Accordingly, which of the statements
55:00are correct? In the 1st. statement, it
55:01said that for the stimuli numbered 1.
55:03and 2., no axon action was formed. It
55:06says it correctly. Look, if I pay
55:08attention here, I don't see any action
55:10potential in 1 and 2. Until where? Until
55:133. It stated correctly.
55:15Is the stimulus now at the? Threshold
55:17intensity value. That is, it is at the
55:19threshold value. Why? How did I
55:20understand? As soon as 3 arrived, a
55:22stimulus was formed. It speaks the truth
55:24. It said that as the stimulus intensity
55:25increases, the impulse speed increases.
55:27No. The intensity, frequency, and
55:28duration of the stimulus would not
55:30affect my speed. I am eliminating this.
55:32Since it asks for the correct one, young
55:34people, what will we say? Our answer, of
55:35course, was that we accepted the first
55:37two.
55:38We will mark 1 and 2 and C. Only 3 was
55:41wrong. The answer to our 2nd. question
55:43became C. Let's come to the 3rd.
55:45question.
55:47It asked which of the changes occurring
55:48in the graphs below is not expected
55:50during impulse transmission when a
55:52stimulus at the threshold value is given
55:54to a neuron.
55:55Friends, heat will of course increase
55:57because what will you do here? You will
55:58spend energy and a certain amount will
56:00come out as heat. Glucose will be used.
56:02Why? Nutrient. Why? Because of cellular
56:05respiration. The amount of spent ATP
56:06will increase because it says spent.
56:08Consumed oxygen will increase. Why?
56:10Because you will perform cellular
56:12respiration here. It says break down the
56:15nutrient with oxygen and give me ATP in
56:18return so I can use it. It speaks the
56:20truth. I am looking at Edirne (E). It
56:22said lactic acid amount. Oxygenated
56:24respiration in nerve cells, friends. We
56:26will not see lactic acid. What was this
56:28lactic acid? It was something we could
56:30see in muscles. We make it without using
56:32oxygen, but neurons cannot function
56:34without oxygen. We even say these are
56:36one of the first organs to be affected.
56:39The brain, that is, we say one of the
56:40systems, not an organ, is the nervous
56:42system.
56:43Of course, I won't see lactic acid or
56:44anything like that. Therefore, I am
56:46marking Edirne and coming to 4.
56:49Below, the impulse transmission
56:50occurring in neurons is schematized. If
56:52you notice, there is transmission in a
56:55neuron in 1 and 3, but what does 2 point
56:57to? The synaptic gap.
56:59And it asks which of the following
57:00cannot be said about the events shown by
57:02the numbers occurring during impulse
57:03transmission.
57:041.
57:06It says the impulse transmission speed
57:08in the first neuron is more than......
57:10the impulse transmission speed in the
57:123rd neuron.
57:13Why? Because, friends, if you notice, I
57:16saw a myelin sheath in 1.
57:17So, because I saw a myelin sheath, I say
57:19that it is faster here compared to there
57:21. Actually, instead of calling it an "
57:23event" here, it would have been more
57:24accurate to say "events and structures.
57:26" 1. The impulse transmission speed in
57:28the neuron, friends, will of course be
57:29faster than in the 3rd one.
57:31Then, in B, it says that impulse
57:33transmission in the 2nd region occurs
57:35via chemical means. Why? Because, if you
57:37notice, this is the synaptic gap. This
57:39place, friends, will be via chemical
57:41means. It says it correctly, with
57:43neurotransmitters. I am looking at C.
57:45The 3rd neuron might belong to the
57:47autonomic nervous system.
57:48Now, here, friends, I had mentioned that
57:50the central nervous system consists of
57:52interneurons and that interneurons are
57:54myelinated.
57:55Look, we are reinforcing this with the
57:56question. Then I say, since the 3rd
57:58neuron is unmyelinated, where could it
58:00belong? It could belong to the autonomic
58:02nervous system. This is already one of
58:04the peripheral nervous system structures
58:06, but we will see the details in the
58:08following lessons.
58:09Let's accept this as true for now. Let's
58:11come to D. Because the wrong answer is
58:13already screaming quite obviously, look
58:15. In D, it says the path followed is in
58:17the form of 1, 2, 3. It will already
58:18proceed in the same way. There is no
58:20problem at all. It cannot start from 2.
58:22It will come from 1 because it is first
58:23.
58:24Then it says it cannot be said, it asks
58:26me that in the question anyway. D can
58:27very well be said.
58:29In E, it says, look, while ATP is
58:31consumed in the transmission in neurons
58:331 and 3, ATP is not consumed in the
58:35transmission in region 2.
58:37Friends, how could it not be consumed in
58:38the 2nd region? Didn't we secrete it via
58:40exocytosis when secreting
58:41neurotransmitters? Therefore, we will
58:43say, no, it is consumed there too. You
58:45are saying it wrong. This clearly cannot
58:47be said, guys.
58:48Therefore, we immediately mark our
58:50answer as E and come to 5.
58:52In the transmission of a stimulus
58:54received by sense organs in a human to
58:55an effector organ, that is, you come
58:57from the receptor to the reaction you
58:58received. It says give me the order of
59:00occurrence of the events here.
59:02Very good. How was it going to proceed?
59:04Receptor, sensory, inter, motor, and
59:06effector. Bravo. Then the impulse will
59:08form in the sensory neuron first. The
59:10interneuron will stimulate and evaluate
59:12this, friends. Between the secretion of
59:14neurotransmitter substance from the
59:15motor neuron and the formation of an
59:16impulse in the motor neuron, which one
59:18should happen? Of course, the impulse
59:20should form first. Meaning, the motor
59:21neuron should be stimulated. Then, the
59:23neurotransmitter should go from its end
59:25toward the effector.
59:27That is why this will come before that,
59:29guys, and what will the order be, look?
59:31It will be 1, 2, 4, and 3. Meaning, we
59:34will mark C. It should be stimulated
59:36itself first so that what? Uh, it can
59:38secrete its neurotransmitters.
59:40I came to the 6th. question. An increase
59:42in which of the above factors increases
59:44the impulse speed? If the diameter
59:45increases, resistance decreases, speed
59:47increases. It says number of synapses.
59:49Friends, now, here, the number of
59:50synapses or the number of Nodes of
59:52Ranvier are not actually evaluated
59:53scientifically. When I see the
59:55transmission speed of an impulse, I
59:56scientifically look for axon diameter,
59:58myelin sheath, and optimum temperature.
1:00:00The intensity of the stimulus and such
1:00:01didn't concern us anyway. We can
1:00:03actually interpret the number of
1:00:04synapses scientifically like this.
1:00:07You can think of it as, the higher the
1:00:09number of synapses, the more exocytosis
1:00:11delays things. I mean, you can think of
1:00:12it as the chemical process there
1:00:14delaying things that much.
1:00:15But when I think of it as a single
1:00:17neuron, that doesn't concern me anyway.
1:00:19I take the axon diameter directly here,
1:00:21friends. Clearly, axon diameter, myelin
1:00:23sheath, and optimum temperature. You
1:00:25take these three, okay? I've come to my
1:00:277th. question. The graph on the side
1:00:29shows the change in impulse speed. I'm
1:00:31looking at the impulse speed, friends.
1:00:33There are X and Y. Okay. It asks what
1:00:35could be correct.
1:00:37When showing the change in impulse speed
1:00:39in X over time, the transmission in X is
1:00:41electrical and the transmission in Y is
1:00:43chemical when I look at the speed.
1:00:46It could be correct. Why? Because the
1:00:48electrical one is faster. So, since X is
1:00:50faster than Y, it could be.
1:00:53In the second premise, it says
1:00:54transmission in X can be observed along
1:00:55a neuron, which is electrical
1:00:57transmission. It could be. It says
1:00:59transmission in Y provides
1:01:00neurotransmitter substances. Since it
1:01:01says "could be," I say it is correct.
1:01:03Because I see it is slower, if you
1:01:05notice.
1:01:05Electrochemicals were faster.
1:01:08Neurotransmitters were slower. Since it
1:01:10asks what could be. I accept all three,
1:01:13young people.
1:01:14Now I've come to my 8th. question.
1:01:16Another graph question. What did I do
1:01:18there in a person touching their hand
1:01:20from warm water to hot water, friends? I
1:01:22increased the intensity of the stimulus
1:01:23. I went from warm to hot. What happens
1:01:25to the impulse transmission speed?
1:01:26Teacher, the intensity, duration, and
1:01:28frequency of the stimulus don't concern
1:01:29us at all. My impulse speed continues
1:01:31just as it started. Good for you. We
1:01:33will solve it exactly like this, young
1:01:35people, okay? I wanted to solve a
1:01:37question like this.
1:01:38And I will solve it. Why? Because we
1:01:40need to know how to place depolarization
1:01:42, polarization, and repolarization. It
1:01:44has shown the change occurring in the
1:01:46axon during impulse transmission. It
1:01:49asks what is correct regarding regions X
1:01:50, Y, and Z, young people. Look, I'm
1:01:52going to tell you something now.
1:01:54We know that the content is normally
1:01:55negative, but what is the only situation
1:01:57where it is positive? If the inside is
1:02:00positive, it is clearly depolarized.
1:02:01There is no other possibility. Because
1:02:03the inside is negative in both polarized
1:02:05and repolarized states.
1:02:06But how will I distinguish them? This
1:02:08sequence doesn't always have to go as P
1:02:10, D, R. The direction of impulse
1:02:12transmission is very important. Pay
1:02:15attention to the question. Look, it says
1:02:17the impulse transmission direction
1:02:18started here and is going towards there
1:02:20. And I found that this area is
1:02:22depolarized, that Y is depolarized.
1:02:23Because the inside is positive.
1:02:25So the stimulus is right here at this
1:02:27moment. Which means, where did it pass
1:02:28just before? It passed through here.
1:02:30Because the direction is this way. It
1:02:32hasn't reached here yet. Then this place
1:02:34is in a resting state. Whereas this
1:02:36place finished the stimulus and returned
1:02:38to its former state.
1:02:40Look, the sequence doesn't always have
1:02:41to be P, D, R. It could also be R, D, P.
1:02:43That's why you won't solve it by rote
1:02:45memorization.
1:02:46You will pay attention to the impulse
1:02:48transmission direction, okay? A very
1:02:49good question. I am moving on to my
1:02:51premises immediately.
1:02:53The first premise says potassium
1:02:55channels open in region X. It says
1:02:57potassium exits to the outside of the
1:02:59cell by diffusion.
1:03:00Since potassium is the customs officer
1:03:02who went on the second break—I say
1:03:04second break—our officer who went on
1:03:06break second was potassium. This was
1:03:08happening during repolarization. The
1:03:09first to leave was sodium. That was
1:03:10depolarization. Number one is correct.
1:03:12In the Y region, the neuron is in a
1:03:13depolarized state. I said that was
1:03:15correct because, as soon as I looked, I
1:03:17saw that its content was positive. In
1:03:19the Z region, sodium gates open, and
1:03:20sodium ions enter the cell. If you are
1:03:22opening the sodium gates and letting
1:03:24them in, this is called depolarization.
1:03:25This process you are talking about
1:03:27happens here, in Y; it does not happen
1:03:28in Z. In Z, the royals are inside, the
1:03:30ungrateful ones are outside, and nobody
1:03:32is going anywhere. Because the
1:03:33sodium-potassium pump is active here.
1:03:36That is, by spending ATP, they are kept
1:03:38outside and kept inside.
1:03:39So, this was not Z, it should have been
1:03:42Y actually.
1:03:43Since it asked for the correct ones, I
1:03:46am marking my answer as 1 and 2, guys,
1:03:48and concluding my lesson.
1:03:51Our first video on the nervous system is
1:03:52finished, guys. I will be waiting for
1:03:54you in the second lesson. I solved your
1:03:56questions and explained your topic.
1:03:57Reviewing is up to you. See you in the
1:03:59next lesson.

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