Right, today we are starting with the Neuroanatomy, very very basic concept, extremely basic concept, right? What is central nervous system? What is peripheral nervous system? What is grey matter? What is white matter?
So and so forth, right? So first of all we start with that nervous system consists of two important components. Number one is Central nervous system right and number two is peripheral nervous system right so nervous system is basically divided into central part and the peripheral part right now in the central nervous system central nervous system consists of brain and the spinal cord Central nervous system consists of brain, brain and spinal cord. Now this area, this all shaded area, this is your spinal cord. Right and this upper structure all the you can see red area this is considered yes please brain.
So central nervous system consists of brain and the spinal cord right. Now what is the basic function of central nervous system? In a very basic concept we will study detail later on. What is the basic function of the central nervous system?
Anyone? Your definition of functions of central nervous system is? No, no, no, no. What is the very basic function of central nervous system?
What central nervous system is doing? Yes, please. It is regulating. One of the functions is thermoregulation. What?
Okay, he also sends signals. What else? Okay, let me tell you very basic function of central nervous system is, it collects the information from environment and the whole body. This is the number one function.
What is the function of number one function of central nervous system is, it should take the information from the environment and from the all body. It collects the information. through the sensory system.
So whole sensory system is giving the information to the central nervous system and central nervous system function number one is it should receive the sensory information. Is that right? Let me make it a very simple diagram that if we say that this is your central nervous system. Right? What is the function of this?
First very basic function of central nervous system is that it should receive the information. Right, this information about the self and the environment should go to the central nervous system. This is sensory input. This is sensory input.
And this sensory system, sensory nerves which are taking information to the central nervous system, they are part of the peripheral nervous system. Number one, it collects the sensory information. Number two, Once the information come here, it compares and contrasts the recent information with the past information. Let me give you an example. I'm standing in this room giving a lecture.
Anyone who is present in the room, right, my sensory system is collecting the information. Here is Irene, here is Carlos, here is Amal, here is Ezra, here is Ronald. How I know that?
My central nervous system knows that because sensations are being collected in central nervous system. through the sensory system for example my visual pathway. Is that right?
Number one. Number two, if someone new enters through the door, again that information is taken to the central nervous system. But as soon as information will go to the central nervous system about the new person, I will compare the new image with the past image and see that can I recognize the person? Is he totally stranger for me or he is a familiar face? So what central nervous system is doing?
Whatever new information is coming, it should compare and contrast with the past information. Because central nervous system has stored lot of information already. So central nervous system receives the sensory input, it stores the sensory input, it compare and contrast and process the sensory input, integrate the present and past experiences and then It decides about the motor response. What should be your response to incoming sensory input?
Right? Then central nervous system will generate the decision. What should be done now?
For example, friend of yours comes. Sensory input is you see the person. Motor may be you give a smile. Or a very good food comes with a very good smell. Sensory input is smell is going.
Sensory input is... you see the good food and motor output will come from central nervous system. Maybe it will start passing saliva or gastric juices.
So what is happening? If someone asks you what is the very basic fundamental function of central nervous system, you must say central nervous system has duty number one that clearly that it should receive all the information which is coming to it through the sensory nerves. Is that right?
Once it receives the sensory information it should process the sensory information, compare and contrast the present and the past sensory experiences. Then it should integrate the new information with previously stored information. Then central nervous system should make a decision what to do.
Right? And then it should generate some motor response. Motor response.
Right? Which may be movement through a muscle. or locomotor system or which may be secretion by a gland or may be changed in the smooth muscle activity like GIT motility change after the food right.
Now this part which receives the information which integrates the information which processes the information makes the decisions and sends the motor output. This system is central unit of the brain. This is the central nervous system and all this system. which is taking the information to the central nervous system and taking the motor information from the central nervous system to the peripheral tissue.
These two together are called peripheral nervous system. So what is the duty of peripheral nervous system? Duty of peripheral nervous system is to take the information from the periphery to the center plus to take the motor decisions from the center to the periphery.
That's so simple. Is it right? We will discuss the functions of central nervous system in big detail later on right but this was just the beginning right now we go to the peripheral nervous system and see what is there.
Peripheral nervous system is naturally divided into two part yes there is motor peripheral nervous system motor peripheral nervous system and yes there is sensory peripheral nervous system. So peripheral nervous system has two part. One part is working as motor part, other part is working as sensory part. Is it clear? Now Okay, so we were talking about the central, sensory nervous system is taking the information from the periphery.
So we say information will flow in this direction, right? And information is going to central nervous system through the sensory. Now, and of course, you know that according to this diagram motor system will generate the response.
So direction of response in our sketch will go like this. So here is the motor response. Am I clear? So this is our central unit that is information input and then information output. Now sensory nervous system is further divided into yes there are special senses There are special senses, senses, yes and there are, yes, general senses, general sensations.
There are special sensations and there are, there are special sensations and there are general sensations. Is that right? Now, what is the real difference?
between the special senses and general senses? What is the difference between the special sensations and general sensations which are going to the central nervous system? Anyone?
Yeah, don't tell me special senses are special senses and general senses are general senses. What is the real difference? Specificity.
You mean special senses are specific and general senses are non-specific. You have to be more specific in your answer. Yes, what is the difference between special senses and general senses? There are many differences. The most important difference is special senses are generated only from a specific part of the body.
And general sensations can be elicited or initiated from many parts of the body. From many parts of the body. For example, touch you can feel from multiple part of the body touch.
So it's a general sense. Is that right? But you can see only through your eyes. Can your ears see?
Or can you see with your lips? You cannot. Right?
There's one specific part of the body which is concerned with the sensation of VN. Is that right? So that should be considered a special sense. We can say special senses are senses which cannot be elicited or sensed through multiple part of the body or from most part of the body.
Special senses can be elicited by specialized designed you can say receptor system which are present in only some specific part of the body. For example, VN. Sense of VN is only from eyes.
Is that right? Then another special sense is olfaction. The smell.
You can smell with your nose. Can you smell with your eyes or with your fingers? you cannot right again olfaction is from special area olfaction smell then this taste you can taste with your tongue but can you taste with your finger no now your tongue your tongue has special sensations as well as general sensations special sense in the tongue is taste the general sense in the tongue is touch temperature now Now touch and temperature you can feel with maybe fingers as well as with your tongue.
But taste you can only feel with your tongue but not with your fingers. So taste sensation become a general sense or special sense? Special sense. Okay.
Then can you tell me some other special sense? Hearing yes you can hear with your ears. You cannot hear with your tongue or you cannot hear with your foot.
Try it someday. You will be frustrated. Right?
So we can say sense of hearing. that is also special sense then sense of balance you know in inner ear has two part ear has two part one is concerned with the hearing which is called cochlear system another is concerned with the balance which is called vestibular system right vestibular system right there's a specialized you can say functional unit which can very accurately determine the sense and generates and sends the sense of about position to the central nervous system. So sense of, yes please, position, right, equilibrium, equilibrium and position, sense of position which is mainly generated by vestibular apparatus of the inner ear, right.
So these are some examples of special senses. Again let me repeat it. What is whole nervous system about?
Nervous system is having number one to collect the information from the periphery, take the information to the center, integrate the information, process the information, make a decision and bring the motor response. Is that right? Information is going to the central nervous system through sensory system. Information is coming from the central nervous system through motor system. Sensations which are going to the central nervous system, some sensations are special sensations, right, which are elicited from some specialized areas in the body.
And there are some other general sensations which can be initiated or elicited from multiple parts of the body. These are called general sensations. The general sensations can be further divided into yes, somatic sensation then Somatic sensations and visceral sensations.
Can you tell me some example of visceral sensation? Sensation which is coming from within the... from the viscera to the central nervous system?
Classical example of that is when you develop abdominal cramps and diarrhea. Those sensations are coming from GIT, right? But visceral sensations are usually from the viscera which may be dull pain.
Pain from the viscera is usually dull but pain from skin is very sharp. So dull pain may be coming from the viscera or There may be discomfort due to distension of viscera. Distension of viscera may lead to discomfort related with the visceral, right?
Or sometimes visceral abnormal movement give a sensation to you, right? So there are certain sensations which are coming from the viscera. Right?
Or from deeper part of the body. Right? Then there are some sensations which are called somatic sensations. Who will define somatic sensations for me?
What are somatic sensations? Anyone? Have you heard of this word or never heard of it? What is really meant by somatic sensations?
Anyone? Have you heard of the word somatic sensations? Which usually include pain, temperature, touch, vibration, proprioception. So what is, how do you define somatic sensations? Somatic sensations are sensations from the, yes, from the skin, right, subcutaneous tissue, superficial areas of the body.
You can say most of the somatic sensations are coming from superficial part of the body as visceral sensations are from the deep part of the body. So somatic sensations are coming from superficial part of the body and somatic sensations are also coming from locomotor system. Locomotor system. What is locomotor system?
Yes Amal, locomotor system. Somatic sensations are for example from the skin, right? Also from the fascias and also coming from locomotor system.
What is locomotor system? The system in the body which is used for locomotion. Locomotion means movement.
It means skeletal muscles. It means movement. joints like capsules, ligaments, tendons, all the sensations from there are also considered somatic sensations and of course somatic sensations are general senses. Somatic sensations may be coming from the temporal mandibular joint or may be coming from the knee joint. Is that right?
So they're generally elicited in the body, right? So somatic sensations are like touch, pain, Temperature and proprioception. First I told you the origin of somatic sensation.
Main origin of somatic sensation is skin and related integument and somatic sensations come from locomotor system. Mainly these two areas and some other areas. What are the types of somatic sensations?
That may be pain, temperature, touch and proprioception. Have you heard of the word proprioception? All of you have heard it. Okay, who is going to impress me by telling this very personal concept of proprioception?
Irene. Okay, this is one component of proprioception. She is talking about the sense of position, right?
So, yes, Ronald, what is your concept of proprioception? Okay, this is, yeah, this is partly right. The same definition you are giving, what Irene gave, that you say proprioception is concerned with how the body parts are...
oriented in the space right any more simple concept all the sensations coming from the locomotor system all the sensations which are coming from locomotor system and going to the center of the system as a group they are called proprioception plus especially sense of position which these two people are telling right so it means that if with my closed eyes If I'm moving my hand, for example, this my hand is here, okay, I move in the air and now I'm not seeing my hand, it is here. I can still bring this finger there. How much central nervous system knew that where is my right finger, right hand?
And how much central nervous system could generate the motor response so that left hand can come accurately to that point? And sensory information was going through this area. Sensory information from the joints, ligaments, skeletal muscles, the tension in them. all of that were computed by the cerebellum to generate the image position of this part.
And then what happened, central nervous system ordered the left hand to go and touch it. And then even corrected it when it overshoot. Did you think if this information was not going to the central nervous system, could central nervous system bring this in right position?
No. Proprioception is very important. All the time central nervous system is computing.
All the sensory input which is coming from joints, ligaments, skeletal muscles, capsules, right, even from skin and from computation of that, all information from constantly incoming information, central nervous system is making its position of the sense of the position of the body parts. Thank God there is proprioception. That when you are walking, do you sometimes while you are walking by mistake, do you lift your both legs off the ground?
You ever did? And all the RG, why you didn't do it? Because when you are walking, center of the system is computing all the information coming from your limbs. And it knows when one limb is lifted off and other should be grounded. Is that right?
For example, another concept of proprioception, for example you want to scratch your ear. Central nervous system already knows where is the ear even with close eyes. And central nervous system really knows where is my finger and it knows I should scratch in this movement. So all this information...
Trillions and trillions of action potentials are moving from different sensory systems to the center of a system and it will compute like a computer and every moment it is deciding how the different parts of the body are oriented in the space. For example, with your closed eyes right now you can tell what is the position of your legs. You are with open legs, she has crossed her legs, he is with open legs, right?
If I asked you to touch your nose, Even with close eyes can you do that or not? Yes. How you know that?
That you are knowing the limb is approaching. Position of the limb, you know it very well, proprioception is going on. So this is very important to know that somatic sensations which are going to the central nervous system, right, they are having a very important component called Proprioception.
Why I am concentrating on this? Because later on in advanced lectures we will study that there are many diseases which disrupt the proprioception and then you cannot walk well. Can you walk well?
Or you can coordinate your movement? Is that right? So this was something about somatic sensations.
We will do every part in detail later on. Visceral sensations, okay. So this is all sensory system information going to that. Another concept, all the sensory information which is going to the central nervous system, are you aware of all the information or not?
No. Some information you are aware and that sensory information which is going towards the central nervous system and you are aware of that information, we say these are the sensations which are going up to the consciousness level. You are conscious of those sensory experiences, but there are some sensory experiences you may not be aware of.
There's some sensory information which is going to central nervous system and central nervous system is processing that information but those informations do not reach to your conscious level and you are not aware of that information. Can you give me some examples of that information that is called as a unconscious? How just most of the time you are not aware of your peristalsis until really something terrible goes with your GIT, right? Excellent example is blood pressure. You know blood pressure is measured by the special sensory systems for example carotid sinus.
From the carotid sinus there are nerves. Carotid sinus right? With changing blood pressure carotid sinus has special nerve endings of the ninth nerve, glossopharyngeal nerve and information goes to the center of the system about the changing blood pressure. You are not aware of that? Is that right?
Then, okay, this was one classical example. So all the sensations which are going to the central nervous system, some do go to the conscious level, then most of them, many of them do not go to the conscious level. Okay, just by the way there's a question.
Which part of the central nervous system determines the level of consciousness? I mean, I say that sensory input has come to the central nervous system. If it goes to a specific part, you will become conscious of the sensation. If it does not reach to specific part, you will not be conscious of the information.
For example, I will tell you, while you are sitting, one minute back you were not thinking about your sense of position. So sense of position was going only to a level which was not processing the information at a conscious level. But if I say, concentrate on your sense of position, then you suddenly know what is the position of your feet, what is the position of your legs, what is the position of your hand you're doing like this, right? So then suddenly it goes jump information jump and it is escalated up to the level of conscious seat. So what is the part of the central nervous system which really processes the information and make you the conscious of the information?
Who will tell me the answer? Yeah? Limbic system is more concerned with the memory, with emotions and with some visceral activity and mood, we'll talk that later.
Which part of the central nervous system is concerned with the conscious? Thalamus has very little conscious appreciation of pain, but not everything. For example, you may be very or I'm very conscious that I'm giving the lecture, what is the temperature here, I know who are the people sitting here, I'm conscious about my activity that I'm delivering the lecture, right?
I should not really reveal my true... self in front of the camera, right? So I'm conscious of so many things and you are also conscious, very careful about answering even though your answers are not coming into audio because our camera system is not taking only my audio, it is so adjusted in you can say way that it is not recording your answers but you are conscious. So which part of the center of our system processes the information at conscious level that if information does not go there, Sensations are there but you don't know.
But if sensations go there to that part of the central nervous system, you become aware of the senses. Yes? Excellent! Irene has given a very good answer. That is cerebral cortex.
So this is the cerebral cortex, right, which is concerned with the consciousness. Whatever information comes, right, it will take it up to the conscious, bring to your conscious level. If some sensory input is going to the central nervous system but that sensory input does not reach to cerebral cortex, right?
Then you will not appreciate that sensation in the conscious way. You will not be conscious of those sensations. For example, sensation of blood pressure. Are you aware of that? No, because that does not go to the cerebral cortex.
But if someone touches me, information is going to the cerebral cortex. So I become aware of that. Am I clear? That's very good answer. Right?
The seat of consciousness is cerebral. cortex. Okay.
Let's go to the motor responses that once the sensations go to the central nervous system, central nervous system will decide, make some decision about. Decision may be not to respond or decision may be to respond. And if central nervous system is going to generate a response, then through the motor system, motor neurons and nerves, information will come to the peripheral part.
Right? There are two types of motor responses. Some of the motor responses can be voluntarily controlled. Some of the motor responses can be under your will. For example, you want to...
Shake a hand with your friend or you do not want to shake your hand. Is it under your will or not? Right? You want to take cup of tea or you do not want to touch the cup of tea. This is under your control.
So some motor responses are under your control. Right? And there are other motor responses which are not under your control.
For example, there is a chicken piece in a plate. Now to hold that chicken piece and to put in your mouth. and chew that is under your control but once chicken piece has gone to your stomach can you tell the stomach don't digest today i will digest it after two weeks gid will work as it wants it is not under your control is that right if there is some lemon here or if there are two three cut lemons here in the plate right to take those lemons and taste them is your conscious But if saliva is being produced, is it under your will?
Under your control? No. No.
So it means motor responses that you will take the lemon and taste it, this is under your will. But even if lemon remains there and you start salivating, that salivation is not under your control. So we can say all the motor responses which are generated by the central nervous system, some of them are. under your willpower and under your voluntary control and some sensations are not under your voluntary control. The sensations which are motor responses which are under your voluntary control these are called somatic motor responses.
Somatic motor responses or voluntary motor responses. Is that right? Opposite to that, those motor responses which cannot be controlled like secretion of glands, they cannot be controlled voluntarily or movement of the smooth muscles cannot be controlled voluntarily or heart rate, can you change your heart rate willfully until you are not very specifically trained in some certain type of special training, we cannot control our heart rate.
You cannot decide to tell your girlfriend that you are very angry but you show her that my pulse is going up. Is it right? Heart rate is not under your control. So it is voluntary or involuntary? Involuntary.
So voluntary responses are somatic motor responses and involuntary responses involuntary responses are automatic responses or we simply call them autonomic motor responses. So what did we learn here? That all the motor responses can be categorized as voluntary motor responses and involuntary motor responses. Voluntary motor responses are also called somatic motor responses and involuntary motor responses are also called autonomic motor responses. Is that right?
Can you give me example of somatic motor response? For example when I move my hand, this is somatic motor response. Is that right? Voluntary motor response. Right?
But if my GIT is right now digesting the grains which I eat in the morning, that is involuntary. GIT is producing secretions, it is producing peristalsis. Right?
Another example, if you see a dog and you see dog size is really big and dog looks very unfriendly, you decide to run away. Now running may be voluntary, but with that your heart rate goes up, that is involuntary. So autonomic nervous system is operating at without your control, right, so involuntary system, automatic system.
Again the motor output in autonomic nervous system is divided into two, sympathetic Nervous system, yes and parasympathetic. Parasympathetic nervous system. Right, usually right now when you are comfortably sitting there is some sympathetic activity in the body as well as some parasympathetic activity. But if you undergo some stress, sympathetic activity will go up. And if you are very comfortable and relaxed, parasympathetic activity will dominate in your body.
Is involuntary dependent on somatic? Yeah. So you only have involuntary if you have somatic?
Yeah, actually all the skeletal muscles we say, the skeletal muscles are under your will. Right? You can control them as you want if you wish to. Right?
But smooth muscles and cardiac muscles you cannot control. Glandular activities you cannot control. Right? So they are said to be controlled by autonomic nervous system and skeletal muscles which are under your control they are controlled by the somatic motor system.
Is that right? For example there's a muscle biceps here. Right?
This is under voluntary control. Thank God! If your limbs are under involuntary control, it will be a terrible situation. You are sitting with Irene and some very beautiful girl pass, and you have involuntary legs, you will be in a terrible embarrassing situation, and maybe for other people disappointing situation.
So thank god, most of the many many muscles and locomotion is under voluntary control. Is that right? And what goes with your poor heart when someone beautiful passes?
Thank God it is not revealed usually to your girlfriend. That is going inside. Is that right?
So you just imagine that your limbs are having all involuntary control. Do you think life will be good? Problem will be especially with the kids.
You cannot take them past the sweet shop. If they have involuntary movement of the lens, all the kids sticking to the sweet shop. You get it?
But there are other things like GIT activity or heart activity or many glandular activities, they are under what is that? Involuntary control or autonomic control. Now this autonomic control which is mainly visceral control, again That is adjusted.
Autonomic motor output has two parts. One is sympathetic output, other is parasympathetic output. You can say that motor output which is coming to the involuntary muscle, either some of it is going to sympathetic output, other is parasympathetic.
Right? Sympathetic output become dominant in the body or increase in the body when you are under stress, fear. Response to fear, you know, when you are afraid your sympathetic activity increases.
Is that right? And what sympathetic activity does? It prepares you for the fright, flight response, right, when you want to run away. It depends on what kind of threat is there.
If you have a small dog, very small dog biting at you, will your sympathetic nervous system go up? No, may be dog sympathetic nervous system go up when you respond to dog. If dog is very small, but dog is big, then your sympathetic nervous system goes up. You get me?
Now, this is automatically. For example, if very big dog is chasing you, right, one thing is you run away. That is voluntary, skeletal muscles. And you know where to run, towards the dog or away? away.
But sympathetic nervous system increases its activity and automatically heart rate goes up. Automatically the blood vessels to the skeletal muscle dilate. Blood vessels to other viscera construct so that blood should be diverted to the skeletal muscles.
Right? When dog is after you and you are really afraid and trying to fly away, what about your GIT activity? It should go up or down? it will go down, you don't want to digest at that very moment the chicken piece you eat.
Otherwise dog may take your leg piece. Is that right? So what really happens is that sympathetic nervous system knows which organ activity should be enhanced in the stress and which organ activity should be reduced.
For example, cardiac activity will go up in stress, but GID activity will go down. Opposite to that, when you are not in stress, you are very comfortable. There's no threat in environment.
You're in a cozy, you can say, bed. Temperature is good. No memories coming which are disturbing you.
You have eaten a very good food. Do you think you are under stress or you are with less stress? Less stress.
So then sympathetic activity will go down and parasympathetic activity will go up. Is that right? That will take the heart rate down.
That will, parasympathetic activity when it increases, heart rate becomes less but GIT activity becomes more. Is that right? So this was very briefly an introduction that what is central nervous system and what is peripheral nervous system.
We already know that peripheral nervous system has sensory nerves which are taking information to CNS and peripheral nervous system has motor nerves which are taking information from CNS to the periphery. Right? then we discuss the central nervous system has a brain and spinal cord and important part of the brain okay let's discuss what is this part of the brain Yeah, this part of the brain. This is forebrain.
This is called forebrain. In the forebrain, this superficial area, right, this is called cerebral... Yes please.
Cerebral hemisphere. Okay, let me make a diagram from the frontal view. As you see, that will make it more clear.
If I'm standing like this and you make a section of the brain, right? Now this is forebrain, here it is midbrain, here these structures hindbrain and this structure is spinal cord. Now cerebral cortex is the gray matter which is present on the surface of this, right?
That I will discuss later. Now first of all this is spinal cord. What is this?
This structure, medulla. What is this structure? Pons and what is this in the back? Cerebellum.
Now pons, medulla and cerebellum. this is as a group called hind brain.. hind brain or other name for this is..
other name for the hind brain is rhombencephalon.. rhombencephalon.. is that right..
then This is the hind brain, here is the forebrain, in between the hind brain and forebrain we are having this structure and this structure should be called midbrain. What is it called? Midbrain. Or other name for the midbrain is mesencephalon. That's very good.
Mesencephalon. So brain has rhombencephalon and mesencephalon. After that, the top area is called forebrain.
This top area. And this forebrain is also called prosencephalon. Diancephalon.
Again please listen. Central nervous system consists of brain and the spinal cord. Brain has hind brain, mid brain and fore brain.
Hind brain is called also rhombencephalon, mid brain is called also mesencephalon and fore brain is called prosencephalon. And out of this prosencephalon, this outer part, this is called For example, this outer part has a different name and this part and deeper structure has a different name. Who will tell me the name?
Out of prosencephalon, there is outer part, superficial area of prosencephalon and there are deep structures of prosencephalon. This superficial structure of the prosencephalon are also called cerebral hemispheres. These are the deepest structures of cerebral hemisphere.
Now these outer structures, what are they called? Telencephalon. They are called telencephalon.
And what is this? Diencephalon. How you can remember that diencephalon is in and telencephalon is out?
You have seen the video? That is why you are answering so well. Okay, I will ask Carlos.
Mr. Carlos, how you will remember that... Keelan Cephalon is outside and Diana Cephalon is inside. You remember there was some princess, beautiful, charming Dianaa.
She was their Rose of England. You remember her? Right.
You just imagine what was happening with Dianaa. Wherever she was, she was the center of attention and there were many many telescopes from everywhere trying to... Not into detail. So what happened here also in central nervous system, here is Dianaa and what are here? What are these?
Telescopes from every direction. Do you think this image, this is a bit emotionally loaded image, can you remember it for long time? So Dianaa has to be in the center and telescopes has to be from everywhere.
Beautiful princess. Our brain is also designed like that. Dianacephalon is in the center and telescopes. Telencephalon is from every direction.
So cerebral hemisphere in the deepest part has been structured. Dianacephalon. and in outer part what are the structures?
telencephalon telencephalon am i clear any question up to this now again let me repeat it that diencephalon is the deepest part of cerebral hemisphere and what is this telencephalons are outer part of cerebral hemispheres but both of them together are called frozen cephalon am i clear to everyone right after this Now before we really go into detail of Neuronatomy, I want to introduce some very basic concept and basic terms related with the nervous system, right? Now nervous system is made of two types of cells basically, right? Nervous system is made of two types of cells.
One type of cells are called neurons and others are what are the neurons? Neurons are the real True functional cells of the central nervous system. Neurons are basically the cells which conduct the information.
The electrochemical information that is called the action potentials. So action potentials are passing through the neurons from one area of the nervous system to the next area of the nervous system. So we can say one group of cells in the central nervous system collectively called neurons have very long processes called axons. Now basically neurons are those cells of the nervous system which are concerned with the communication signals. Is that right?
They are taking the action potentials. Then there are other cells which are not neuronal cells but they are present in nervous system. The other group of cells are supporting cell to the neurons.
The true functional cells of the central nervous system are neurons and the other cells which support the neurons, right? They act as a connective tissue for the neuronal cells. Now what those cells are called as a group? Again let me repeat. Central nervous system is made of primarily two types of cells.
One type of cells which are conducting the information, which are the true central nervous system cell, right? which are doing the true function of nervous system, taking the action potential from one area to another area. Is that right? Releasing the neurotransmitter, generating the action potential. Is that right?
Those cells are called neurons. Then there are many other cells which support the neurons. We call them connective tissue cells of the nervous system. These connective tissue cells of the nervous system as a group, they are called glial cells, neuroglial cells.
What are they called? Neuroglial cells. Is that right? Neuroglial cells.
So central nervous system has two types of cells. There are neuronal cells and neuroglial cells. Neuronal cells are the two functional cells of the central nervous system which are generating action potentials and conducting action potentials and Neuroglial cells are the supporting cells of the nervous system.
About the neuroglial cells I will go into detail later. But I will now introduce some very basic terms about the center of a system in relation to the neurons. For example, when you study neuroanatomy and neurophysiology, you come across two terms very frequently. One term is gray matter and another is White matter.
Everyone who is studying Neuroanatomy and Neurophysiology, even Neuropathology, he comes across again and again the terms of gray matter and white matter. So Ronald is going to tell us what is gray matter. These are the cell bodies of the neuron.
Let's suppose cell bodies of the neurons are present in the ganglion also. Autonomic ganglia? Do you think autonomic ganglia are gray matter? No.
No. By your definition, it is but they are not agreed by other doctors. He says that cell bodies of the neurons are called gray matter.
Mostly he is right. But I put an objection to him that cell bodies are collected in the autonomic ganglion also. Cell bodies of neuron. But autonomic ganglia are not called gray matter because gray matter is only in Central nervous system and autonomic ganglia are a part of peripheral nervous system. His definition need a little refinement.
Actually collections of cell bodies within the central nervous system are called gray matter. Let me tell you, cell bodies of what? Cell bodies of neurons. Neurons are like mouse, rats. So this is one neuron and what is this long tail?
What is this tail? Axons. What is this tail?
Axons. Now in some part of the central nervous system if there are many rats together and these are the tails right now these cell bodies because they have the nuclei right they look gray Now this collection of the cell bodies within the central nervous system, within the central nervous system, this collection of cell body is called gray matter. When we say there is cerebral gray matter, it means in the cerebral hemisphere, in some area lot of cell bodies of neurons are collected together.
So when all these body of the rats together, this is gray matter. And all their... tails put together are called white matter.
So when in the central nervous system we are talking about here's gray matter and there is white matter, what really should come to your mind? Gray matter means that in that area there are lot of cell bodies of neurons and white matter means that that is the area where there are lot of axons together because axons have some myelin sheath and they look somewhat white color and Cell bodies when they collected in one area, cell bodies have you know nucleus, DNA, RNA all those structures impart darker color to the brain substance right. So now again I will repeat in central nervous system a lot of cell bodies of the neurons are put together that is called gray matter and if lot of axons are put together that is called white matter is that right. Now We can say now that nervous system again will divide into central nervous system and yes please peripheral nervous system but now we are talking not functionally we are talking structurally.
In the central nervous system where lot of cell bodies are collected these are the cell bodies right collection of cell bodies what is it what is that gray matter right so we divide it like gray And plus central nervous system has yes white matter. Is that right? Grey matter we can show by many many cells there, neuronal cells.
Right, this is the grey matter. And what is this going? Yes, white matter. I hope you will remember this now. Whenever someone says there is a disease of white matter, it means this is concerned with Axonss.
If we say there is damage to gray matter, it means lot of cell bodies are damaged. Is that right? Then gray matter is further divided into two types. In the central nervous system, gray matter is divided into two specialized types. Some are called cortex and others are called nucleus.
Have you heard of like third nerve nucleus? Vagus nerve nucleus, have you heard of it? Vagal nucleus in central nervous system? Right?
Now some of the gray matter is called cortex and some of the gray matter in central nervous system is called nucleus. What is the difference between cortex and nucleus? Question goes to Ventura. You have heard of it? There is cortex in the brain and there are some nuclei in the brain.
What is your real concept? Jessica please, she is going to impress all of us. Yes we have a new friend there. Do you have any idea the difference between the cortex and nucleus? When we study neuron anatomy we say there is cerebral cortex, there is cerebral cortex, many diseases related with that.
We talk about third nerve nucleus, sixth nerve nucleus. Do we talk or not? We talk about nucleus for salivation, nucleus for lacrimation.
Women are very much special. Nucleus for lacrimation, nucleus for taste. We call it nucleus of practice solitarious, vagus nucleus. So what are these nuclei and what are these, what is this cortex?
Should I tell you or you can guess yourself Amal? Try to guess something because very basic of central nervous, yeah that's very good. She come up with some good idea.
Let me tell you here is suppose I draw the central nervous system. Side view right, now listen the gray matter, the gray matter which is applied on the surface of the central nervous system is called cortex. Sometimes actually there are lot of cell bodies you know which are collected, which are collected on the surface of what is this?
Forebrain, cerebral hemi Sphere so what is this area there are a lot of neurons with their yes Cell bodies and these neurons with their cell bodies right all the structure where the neuronal cell bodies are abundantly Present this this is a gray matter of course But because this is applied on the surface of the cerebral hemisphere it is exposed on the surface of the cerebral hemisphere This is called cerebral cortex. What is it called cerebral cortex? Opposite to that, you know that here is cerebellum. What is here?
Cerebellum. And there is also a lot of neuronal cell bodies here and they are making this gray area and this gray area which is also exposed on the surface of cerebellum. This is called cerebellar cord.
So this is cerebral cortex, this is cerebrial cortex. What is cortex? Cortex is just a gray matter exposed on the surface of the brain.
What is gray matter? Gray matter is the collection of neuronal cell bodies. It's a difficult concept.
It's so easy, isn't it? Now this is cerebral cortex, this is cerebrial cortex. Now from here let's suppose that from these neurons There's...
what is this? There are axons. Suppose the axons are going down. Now what this all collection of axons which are going down, what is this?
White matter. What is this? White matter.
Many axons connecting like this here. So what is this? White matter. Many of the fibers coming from the top and then going to cerebellum.
What is this? White matter. Many fibers going from down to top, is that right?
and then going here, what is this? white matter. many connections from here going to the backward, what is this?
white matter. many connections from here connecting to the front, again what is this? white matter.
is that right? now you know the real difference between grey matter and the white matter? that in central nervous system where cell bodies are connected is grey matter.
and when there is abundance of the Axonss together they are called white matter and when grey matter is applied exposed on the surface of the central nervous system then it is called cortex and there's another term used nucleus. Please nucleus of the central nervous system should not be confused with those nuclei which are present in the cell which are called nuclei which have DNA. Nucleus term is used in two different meaning.
Number one You know within the cell there's a nuclear membrane housing all the chromosomes that is called nucleus but in central nervous system nucleus term is also used in a different different context when we say there's third nerve nucleus what does it really mean yes who will tell me have you heard of this concept is vagus nucleus third nerve nucleus fifth nerve nucleus you never heard of these things anyone heard of you Jessica must have heard When you study neuroscience you say third nerve nucleus is damaged and person will develop some problem with the eye movement. Yeah nuclei are special. Now let me tell you one thing before you tell me something totally new.
Listen. Sometimes what happened there are some cell bodies collected here. Is that right?
And this collection of cell bodies of course is a piece of grey matter. But this piece of grey matter from all sides is surrounded by what? This is surrounded by what? White matter.
So pieces of grey matter which are embedded within the central nervous system and surrounded by white matter are called nuclei. They are called nuclei. Now if from this piece of grey matter all the axons are going out and making the seventh cranial nerve, let's suppose all these exhausts going out and making seventh cranial nerve, then this nucleus will be called nucleus of the seventh cranial nerve.
So we say that seventh cranial nerve have a nucleus. It means that in the central of a system there is a small piece of gray matter and because and it is surrounded by white matter, so this must be called nucleus and from this nucleus many fibers are going out. These are the rats from here where tails are going out and making seventh nerve.
So we should say this is a nucleus of seventh nerve. So next time when you study this nucleus of third nerve or nucleus of 12th hypoglossal nerve you must get an idea. So what is meant by the nucleus? This is a small piece of gray matter surrounded by the white matter and if it is 12th nerve nucleus, it means 12th nerve axons are connected to that gray matter. Rather those axons are coming, suppose here it is 7th nerve axons, they are coming from the nucleus of the 7th nerve.
Right? So what we can say? That gray matter, gray matter is divided into cortex and nucleus.
Right? What is cortex? Cortex is the grey matter which is exposed on the surface of the brain.
What are nuclei? Nuclei are the pieces of grey matter in the deeper part of central nervous system surrounded by white matter. For example, there are many many big collections of grey matter in this area, in the very deepest part of cerebral hemisphere. There are multiple pieces of grey matter here surrounded by the white matter.
So as a group and they are controlling many motor functions. So these pieces of gray matter in the deepest part of cerebral hemisphere rather these pieces of gray matter in the base of the cerebral hemisphere in the base of cerebral hemisphere these are called basal nuclei. What are they called? Basal nuclei. Is that right?
Now I will ask a question and you have to answer. In the central nervous system has two types of cells. Some cells which are doing the true function of conduction.
What are those? Neurons. Other group of cells which are sporting the neurons.
What are these? Neuroglia. We'll go into detail of neuroglia later. Now neurons have a cell body and usually a long process called axon. Those area of central nervous system where cell bodies are put together they are called?
They are called? Gray matter. They are called? Gray matter where cell bodies are put together.
And this grey matter is the surface of the some brain this is called cortex. If this species of grey matter embedded with deeper part of the brain and surrounded by the white matter then they are called nuclei. Am I clear? Now let's come to the some detail of white matter. Right?
You already know that white matter is that part of the brain in which there are a lot of axons put together. They are not rats but they are tails of the rats. Is that right? So that is white matter. There are the cables.
Right? Now. White matter can be classified in many ways.
One of the ways is the direction in which directions in which these axons bundles are moving. For example some axons or bundle are moving up and down along the neuronal axis, neuro axis right. For example many many sensory information fibers come in and then they go upward. and lot of motor information is decided from here and motor fibers come down. So it means there is some white matter which is of course group of axons which are taking the information to the upper level.
And there is some more white matter right or group of axons which are taking the motor responses downward. Is that right? For example someone scratch on your feet.
So what will happen? From your foot This information is going like this. Now what is this? This is white metal system taking the information up and then you decide to remove your foot. Then what will happen that from here information will come down and go to the muscles here.
So it means in neuronal system there are a lot of fibers which are going up and down. These are called as a group. Because some fibers are taking pain information, some fibers are taking touch information, some fibers are taking vibration information, some fibers are taking pressure information. In the same way there are fibers coming down which bring somatic motor responses, some fibers coming down and bring autonomic responses. So all these fibers which are going up and going down as a group they are called yes please who knows excellent they are called tracts right.
So when we say that any fibers which are moving, you can say from down to up in central nervous system or up to down as a collection they are called pracs and those bundles of axons which are taking information from lower part of the central nervous system and taking information to the upper part of the central nervous system, those are called ascending pracs. What are they called? Ascending pracs. So we can say There are some white matter which is taking information?
Yes, Sphalically and caudally. Sphalically? Sphalically means upward and caudally means downward and these bundles are called yes, tracts. So now you know the tracts in the central nervous system. The tracts are the bundle of axons which are taking information up and down.
Is that right? Of course, then tracks which are taking information upward, they are called ascending track. Ascending tracks which are taking the information upward. And then those tracks which take the motor responses and information from top to down, they are called? Yes?
Descending track. Am I clear? So what are tracts?
Tracts are the white matter bundles which take information up and down in the center of the system. Right? Fine?
Now there are some more bundles or white matter or axons which connect the right part of the brain with the left and connect the left part of the brain with the right. For example If I draw the central level system like this, tracks are moving up and down. Is that right? Then there are some pathways which are connecting right to the left and left to the right.
The spinal cord as well as in cerebral hemispheres and many other areas. There are some bundles of white matter which are connecting. Today I have little bit fluke. So my sound is something different. Now what I am talking about that there are some white matter connections that which are connecting the central nervous system components right to left.
Is that right? What are those called? Corpus callosum is one of the example of that but there are many connections. One of that is corpus callosum which is the largest.
Corpus callosum is a very big bundle of white matters which are connecting the right cerebral hemisphere with the left and left with the right of course. Right? But there are many other which are also connecting right and left areas in central nervous system. As a group such fibers are called what type of fibers? They are called commissural fibers.
Have you heard of commissure? They are called? Yes? Commissural fibers. So next time when you think there are some fibers in the central nervous system which are tracked, you know they are connecting up and down.
And next time If you read somewhere there are some commissural fibers then these are group of fibers which are connecting the central nervous system right and left. Am I clear? Commissural fibers.
Is that right? Corpus callosum is the largest commissure. Corpus callosum is a very big heavy information cable between the right hemisphere and the left hemisphere.
Corpus callosum. Then Not only, attention please, central nervous system not only should be connected up and down, not only should be connected right and left, it should be connected front and back also. For example, for frontal lobe, information should be connected with occipital lobe and information from occipital lobe must be connected with the frontal lobe, right.
It means that there should be bundles of white matter which should connect brain's central nervous system components entro posteriorly or postro anteriorly. Am I right or not? So that cable system, that neuronal system, that axon system, that white matter system, that information cable system which connect anteriorly and posteriorly, central level system, that cable system is called what type of fibers? When we say tracks, they are up and down connections. When we say commissure, they are right and left connections.
Now we want Front and back connections. What are those fibers called? It's just ABC of neuro anatomy we are doing.
You must be knowing. They associate the anterior part with the posterior part of the brain and they associate the information from posterior part of the centromolar system to the anterior part. Thank god they have no complex name.
These fibers which associate the information from enter posteriorly they are simply called as Association fibers they are called association fibers right so you can say look here now the fibers which connect from here to here or fibers which connect from here to here these black fibers are association fibers red fibers are up and down these are the tracks and some fibers right and left and these are commissural fiber have you heard of these things oh you know what is gray matter what is white matter gray matter has Cortex which is exposed on the surface. It has nuclei which are embedded within the white matter, pieces of grey matter. You have white matter.
White matter is vertical tracks. They are right left commissural fibers. They are interposterior and they are called association fibers. They are called association fibers. Right?
Then I will tell you something interesting. Have you heard of the term reticular formation? Have you heard of the term reticular formation in neuroanatomy? You've heard it, isn't it?
What is reticular formation? You don't want to share your knowledge. Very secretive about knowledge. You know as old Hukma was there.
All time the people who are healers they keep the knowledge to them they don't share and tell anyone what is radicular formation. Let me tell you. Actually in the spinal cord if I make a section of spinal cord, in the spinal cord this is the gray matter which is in the center. In the spinal cord gray matter column is moving in the center and on the side what is there? White matter.
Is that right? And in the top part of the brain grey matter is outside. Are you getting me?
Here in the spinal cord grey matter is in the center and white matter is outside. In upper levels of the brain grey matter is outside and white matter is inside. So when these white matter fibers are going up and down, they make...
Here is your... Brainstem. This is your brainstem from here to here.
Right? Now this grey matter column is going centrally. Grey matter column is going centrally upward.
This is grey matter column. And on the side what it has? White matter.
Now what really happens? As these fibers are going up, as well as fibers are coming down, right? Actually in the brain stem, these fibers make major crossing. Sensory fibers. go to the opposite side and go to the opposite hemisphere.
In the same way, fibers which are coming down motor, they also make in the brain stem crosses. Because fibers from the left hemisphere are coming to the right spinal cord. Right motor fibers, which are descending fibers.
And from the right hemisphere, they are going to the left side. It means, when motor fibers are coming down, they decussate, they cross. In the same way, when sensory fibers are taking information up, Right? Some of the fiber as they enter in spinal cord they cross. But some of the fibers they cross in the brain stem.
It means in the brain stem there are major motor crossings and the major sensory crossing. So when in the brain stem sensory fibers are crossing and motor fibers are crossing, do you think gray matter will remain intact? No. Because crossings will occur through that.
Grey matter. So grey matter will break down into small pieces and you will have some area, you will have some area in which grey matter and white matter is mixed. This is the area in which central gray matter is there but lot of fibers are crossing motor and sensory.
So gray matter become into small pieces. It become fragmented into small pieces and through these pieces white matter is passing. Axonss. So we say this area become a network of gray matter and white matter.
This part of the brain stem become network of gray matter and white matter. This network is called reticular formation. What is it called? Reticular formation.
So what is reticular formation? Reticular formation is just that part of the deeper part of the brain stem where due to major sensory and motor crossings gray matter and white matter mix and that is called that is called reticular formation right but during this crossing some gray matter pieces are intact as large pieces And these large pieces are called nuclei. That is why in the brain stem many grey matter when it disintegrate due to major crossings, grey matter break down to fragments. Some fragments are large and these large pieces of grey matter are called nuclei. So brain stem has lot of nuclei and brain stem has also Reticular formation, reticular formation when grey matter and white matter truly mix and nuclei are that some big pieces of grey matter are surrounded by the white matter within the brain stem.
Is that okay? Okay then one simple question, what is nerve? Of course it's peripheral nervous system, what is nerve? Collection of axons outside the central nervous system.
Now listen carefully. Collection of axons within the central nervous system is white matter. Collection of axons within the central nervous system is white matter. And collection of axons outside the central nervous system are called nerves. That is so simple.
Is that right? It means when we say there are tracks in the central nervous system, tracks are just bundles of axons going up and down. But bundle of axons going from central nervous system to the periphery are motor nerves.
And bundle of axons collecting information from peripheral part of the body and taking to the center are sensory nerves. So what are nerves? Rather question can be put like this to make a concept very clear.
What is the difference in nerve and track? You say there is something common something different. What is common? Tracks are also bundles of axons, nerves are also bundles of axons.
The difference is that nerves are outside central nervous system and tracks are inside. Tracks are also information cables going up and down. And nerves are also information cables.
Is that right? Another very big difference which I later on I will tell you that for insulation purpose nerves have special cells called Schwann cells. I will teach you later. and for insulation purpose tracks have white matter as special cells called oligodendroglia. So around the neuronal axons of the nerves there are Schwann cells and around the tracks or white matter in the center of a system there are no Schwann cells rather different type of cells which are called oligodendrocyte.
Why I am highlighting this point? Because some diseases attack only Schwann cells, so they demyelinate peripheral nervous system. The other diseases which attack only oligodendrocyte, so they demyelinate central tracts.
There are some diseases which attack the Schwann cell as well as oligodendrocyte, so they produce demyelination or conduction problem with the peripheral nervous system as well as central nervous system. Right? That's all for today.