Neurophysiology Grab your piece of paper, grab your pen and let's go! Hello and welcome to MK Secrets of Neurophysiology. My name is Dr. Moses Kazevu. This is a new series on my YouTube channel where we'll look at neurophysiology topics in depth, covering the whole syllabus. I know fourth year medical school or the second year of medical school, depending on how your school calls it, is very challenging. So I decided, why not? Let's review each and every single topic and make this as easy and as fun as possible. So in this review lecture video, we're going to be talking about the introduction to neurophysiology and giving you an overview. of what you have to expect during the course of the classes as well as during the course of the academic year if you haven't yet subscribed to the channel please hit the subscribe button hit the bell notification icon to be receiving notifications of such updates every time i post grab your piece of paper then grab your pen and let's go so you Welcome to neurophysiology and we're going to be talking about pretty much the introduction to neurophysiology, the divisions and the parts of the nervous system, the functions of the nervous system, as a foundation to each and every single topic that we're going to be discussing concerning neurophysiology. It is a very interesting field to actually learn, a very interesting subject to learn, and if you actually pay close attention, you will learn a lot and you will be able to actually put most of these things that you learn in neurophysiology in practice when you reach your clinical years. So remember that the nervous system is this complex network that allows organisms to communicate with the environment. Just like a cell phone network company allows you to call an individual that's miles and miles away from you, the cells in the body also communicate with each other via the nervous system. They communicate with the external environment via the nervous system. And remember that this environment can either be both External, meaning the world outside us, we're able to see things, we're able to hear things, we're able to taste, we're able to smell things. And the internal environment, which is pretty much the components and cavities that are present inside the body. When you're talking about the nervous system, it's going to be divided mainly into two parts. There's what is known as a central portion, which is known as the central nervous system, consisting of mainly the brain and the spinal cord. Then everything outside the central nervous system is referred to as the peripheral nervous system. So I shall abbreviate central nervous system as CNS. I shall abbreviate peripheral nervous system as PNS. And the peripheral nervous system is going to be further subdivided into a somatic. component somatic meaning body and this is going to be under voluntary control as well as an autonomic component which is automatic from the word automatic meaning it's under involuntary control now remember that the nervous system has pretty much three basic functions it has sensory function which is pretty much going to be bringing information towards the nervous system it's going to allow you to detect changes in the environmental stimuli it could be changes in the amount of light It could be changes in the amount of sound. It could even be changes in the amount of pressure across your skin. Then there is a motor component which is going to be generating movements, is going to be causing contractions of skeletal muscle, cardiac muscle, smooth muscle to carry out the respective functions. If skeletal muscle contracts, of course an individual is going to move. If cardiac muscle contracts, the heart is going to beat. vessels are going to reduce in their size glands are going to produce their secretions then the nervous system pretty much also has an integrative function so you can think of this as a part where they are going to receive store process sensory information and then orchestrate a plan or an appropriate motor response so you can think of this as the thinking station where you're going to be getting this sensory information you make sense of what the sensory information is, then you formulate an action plan and you actually execute that action plan. So these are the three fundamental roles or the three fundamental functions of the nervous system, the sensory function, an integrative function, and a motor function. Now here's a schematic of how the nervous system is actually going to be divided. So here you have the nervous system, you have the central nervous system over here, the peripheral nervous system which is divided into a sensory component and a motor component. The sensory is also known as the afferent component, afferent A. Remember A comes before E in the alphabet. So A for sensory going into the peripheral nervous system then E coming out of the peripheral nervous system efferent or motor the motor component can be voluntary which is the somatic component or involuntary which is the autonomic nervous system and remember that the autonomic nervous system is largely divided into two main systems we shall talk about the autonomic nervous system towards the end of the syllabus and But for now, just know that the autonomic nervous system is going to have a division that's known as the sympathetic division or the thoracolumbar division and a parasympathetic division which is known as the craniosacral division. Moving on now, we shall talk about each of the parts of the central nervous system, as well as each of the parts of the peripheral nervous system, so you get an overview before we actually dive into first beginning to discuss about the sensory system, then we shall move on to the motor system and some higher function centers and some higher functions in the brain, and that's how we will progress during the course of this review lecture videos. Now, in the central nervous system, you have pretty much the brain and the spinal cord. Remember that The nervous system is pretty much going to be made up of two cells. Every organ from your physiology and from your histology, you already know that organs are going to be made up of a functional tissue, which is referred to as the parenchyma, and a stroma, which are the supporting tissues. So the functional tissue of the nervous system is of course the neuron, which I'll talk about neurons in the next lecture, and receptors as well. Then there are also these supporting cells which are known as neuroglial cells or neuroglia. So these neuroglial cells are of different types. You have astrocytes, you have ependymal cells, you have oligodendrocytes, you have Schwann cells and you have microglial cells. Those are the types of neuroglia that are present inside the nervous system. Remember the Schwann cells are found in the peripheral nervous system and the other cells are found in the central nervous system. So you have the astrocytes, the oligodendrocytes, the ependymal. cells and the microglial cells are found in the central nervous system but the Schwann cells are found in the peripheral nervous system and each of these are going to be having specific functions that they're going to be carrying out and remember that the brain and the spinal cord are going to be arranged in two types of matter there's what is referred to as gray matter and what is referred to as white matter gray matter the reason why it's gray it's because of this the nasal bodies or the nasal substance that is found in the cell bodies and even the proximal parts of the nerve fibers that are going to be arising from the cell body so Pretty much, if you're talking of cell bodies, you refer to that as gray matter. It's going to appear grayish in color. Then white matter is pretty much the remaining parts of the nerve fibers, which are the axons. So a collection of cell bodies that is going to be found in the central nervous system is going to be referred to as a nucleus. Singular is nucleus. Plural is nuclei. So I'm sure you've heard of certain nuclei that are present. For example, the nucleus tractus solitarius, which is a nucleus that is present in the central nervous system. But there is an exception to this rule, or rather I like to call it a misnomer. There is a part that's known as the basal ganglia which consists of a collection of nuclei. This should actually be called the basal nuclei because these are found in the central nervous system as opposed to them being found in the peripheral nervous system. And the arrangement of white matter and gray matter differs when you're talking about the brain and when you're talking about the spinal cord. When you are talking about the brain, the white matter is going to be found on the inside, the gray matter is going to be found on the outside. How I like to remember this is that in the brain we all have a little white inside of us. No racial comments intended or anything that's racial on this channel. We do not promote any of that but it's just a way to help you remember the concept. Then in the spinal cord, the white matter is going to be found on the outside while the gray matter is going to be found on the inside. We shall talk about a lot more details of this as we go further and further into these review lecture videos then we move on we move on to the peripheral nervous system remember that the peripheral nervous system has a sensory component and an efferent component or a motor component remember that the sensory component is also known as the afferent this is taking information towards the central nervous system then the efferent is known as the motor which is going to be taking information away from the Central nervous system where the central nervous system acts as an integrative center. So remember that this is going to be including sensory receptors which can either be visual receptors which are found in the eye, the photoreceptors, auditory receptors which are the hair cells that are found in the inner ear, chemoreceptors which could be found on the tongue, and somatosensory receptors which are found on the skin which we shall do in the subsequent lectures. Then you have sensory neurons that are present which are going to be carrying information from these receptors to the central nervous system. You have ganglia which are a collection of cell bodies in the peripheral nervous system. Remember that. The collection of cell bodies in the central nervous system is referred to as a nucleus, plural nuclei. The collection of cell bodies in the peripheral nervous system is known as a ganglion for singular, ganglia for plural. Then of course you have a somatic motor neurons as well as autonomic motor neurons. The somatic motor neurons carry out voluntary functions, while as the autonomic motor neurons are going to be carrying out automatic functions. And the autonomic nervous system is going to be divided into two parts a sympathetic nervous system Which is coming from the thoracic division of the spinal cord as well as the lumbar division of the spinal cord Hence it's going to be referred to as the thoracolumbar division of the autonomic nervous system Then the person but that division is going to be coming from some cranial nerves as well as some sacral nerves So this is referred to as the cranial sacral Division and remember that the peripheral nervous system is going to be consisting of some cranial nerves about 13 or 12 rather cranial nerves that are going to be there and arising from the brain as well as the spinal cord 31 pairs of spinal nerves that are going to be arising from the spinal cord now remember that the peripheral nervous system is going to be providing an interface between the environment and the central nervous system so it's going to be kind of like a relay center or a relay place and the sensory or afferent divisions that are going to be bringing information towards the nervous system and usually this begins with the sensory receptors. So the receptors are the cells that are able to sense changes in the environment. stimuli and they can pick up these changes and they can transduce so transduction is the conversion of one energy form to another so they can transduce for example sound energy into electrical impulses they can transduce light energy into electrical impulses and then these are going to be carried along these sensory neurons and then of course the afferent information is going to be transmitted from the higher centers from the higher levels of the nervous system and This is going to be carried with the motor division or the afferent neurons to the peripheries where it's going to cause contraction of skeletal muscles, cardiac muscles, smooth muscles that are eventually going to bring up their characteristic functions. Again here's a diagram showing you the schematic of the nervous system. You have the central part, the peripheral part, which is divided into a sensory or afferent part, a motor or afferent part. The efferent part is divided into a somatic or voluntary component and an involuntary component which is known as an autonomic nervous system. The autonomic nervous system is divided into a sympathetic division and a parasympathetic division. The sympathetic division is also referred to as the thoracolumbar. The parasympathetic is also referred to as the craniosacral. Now moving on to the brain, the brain embryologically is going to be consisting of three major divisions. You have what is referred to as the forebrain which is also referred to as the prosencephalon. Then you have the midbrain which is referred to as the mesencephalon and you have the hindbrain which is referred to as the rhombencephalon. So you have the... the front brain or the forebrain, the midbrain and the hindbrain. So the forebrain is divided into two main parts. You have the telencephalon which is going to be consisting of the cerebral hemispheres, the basal ganglia, the hippocampus and the amygdaloid nucleus. Then you have the diencephalon which is going to be consisting of the thalamus, the hypothalamus, the metathalamus and the subthalamus. You have the mesencephalon which is the midbrain consisting of the brainstem pretty much. going to be these parts that are found in the brainstem, the midbrain. Then you have the rhombencephalon, which is divided into the metencephalon, which is going to be consisting of the pons and the cerebellum. Cerebellum just means little brain. Then you have the myelincephalon, which is going to be consisting of the medulla oblongata. Then here is a schematic again. So you have the brain divided into a forebrain, a midbrain, and a hindbrain. Then the forebrain is divided into the telencephalon which consists of these parts that I already mentioned. The diencephalon is going to be consisting of these parts. The mesencephalon is going to be pretty much the midbrain. Then the hindbrain is going to be the pons and the cerebellum as well as the medulla and the blankata. So here's another schematic of the representation of these structures that I've been talking about. So here you have the different lobes of the cerebral hemispheres, the frontal lobe, the parietal lobe is here. Here you have the occipital lobe and the temporal lobe has been removed on the side, but you can see it peeping underneath there on the other side. Then this structure here is referred to as the thalamus. Then here you have the hypothalamus. An extension of the hypothalamus is the posterior pituitary gland. You. As well as the anterior pituitary gland which develop from different structures But we shall talk about this when we look at the pituitary gland you have the midbrain You have the pons and the medulla which collectively form what is known as the brain stem Then you have the cerebellum which is joined to the pons and then the spinal cord over there so those are the basic basic parts of the brain and the central nervous system. Then the parts of the nervous system that we'll talk about, we'll look at spinal cord and the spinal nerves. We'll look at the brainstem, the functions of each of the parts of the brainstem, the cerebellum and its functions, the diencephalon, pretty much the thalamus and the hypothalamus. We'll look at the cerebral hemispheres, the cerebral cortex, the white matter, the basal ganglia, the hippocampal formation, as well as the amygdala. So speaking of the spinal cord, remember that the spinal cord is the part that's going to be most caudal. So caudal just means inferior or rather the lower parts, if I could say in layman's terms. So the caudal portion of the central nervous system, so it's going to be extending from the base of the skull to the first lumbar vertebra. So it's going to be extending from the base of the skull to L1. then it's going to be consisting of 31 pairs of spinal nerves. These 31 pairs of spinal nerves are going to be containing both sensory components and motor components. So it means that spinal nerves are mixed entities. What do I mean by mixed entities? They're going to be consisting of both sensory nerves as well as motor nerves. And these 31 pairs of spinal nerves are divided as follows. They have different regions. And remember that they come out from the vertebra. So let me just give you a whiteboard here. so that I can or rather a blackboard here so that I can explain this concept very well so I would draw these boxes here to represent the spinal the vertebral column which are the bones so these are the bones here so let's say this is c1 the first cervical and this is c2 the second cervical bone so remember that these nerves are coming out below here in between these bones so they're going to be coming out like that one on the right side one on the left side and then here you have c3 so you have 31 pairs that are going to be coming out in this fashion below the subsequence so c1 the c1 bone will be on top of the c1 nerve okay So you have 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. Now how I like to remember this, I just like to remember the times that I have my meals. So let's say you wake up early, you have your breakfast at 8 hours, then you have your lunch at 12 hours. I don't know who has lunch at 12 hours but there are some individuals that do. Then you have supper at 17 hours or you can say 5. p.m and if you if you're like me then you have two meals at 5 p.m so you have five lumbar five sacral and then of course at zero one you have a post midnight snack so if you remember this and you remember your eating times it's very easy for you to remember how many pairs of um how many pairs of cervical spinal nerves are there how many pairs of thoracic lumbar sacral and coccygeal and remember that information in this spinal cord is going to be traveling along pathways there are predominantly two main pathways that are found in the spinal cord You have the ascending pathways that are going to be carrying information that is sensory from the peripheral aspects to the higher centers or to the higher levels of the central nervous system. Then you have descending pathways that are going to be carrying information in the spinal cord from the higher centers to the peripheral nervous system. So it means that the ascending pathways are sensory pathways, while the descending pathways are motor pathways. Then moving on to the brainstem is going to be consisting of the medulla, the pons and the midbrain and it has 12 cranial nerves. So correction back then when I say 13 cranial nerves, they actually 12 cranial nerves. Apologies for that. So you have 12 cranial nerves that are going to be present arising from the brainstem and the 12 cranial nerves are as follows. You should know all 12 cranial nerves by name and by number and preferably even by function and whether they are motor or sensory. We shall have a lecture just on cranial nerves. to look at the 12 cranial nerves and whether each of these are motor, sensory or mixed and their names. So the first cranial nerve is the olfactory nerve, which is cranial nerve number one. The second is the optic nerve. The third is the oculomotor, then followed by the trigeminal, then the utrochlea, the abducens, the facial, the vestibulocochlea, the glossopharyngeal, the vagus, the accessory nerve and the hypoglossal nerve. So... How I remember this, I have a mnemonic O O O to touch and feel. Very good velvet and help. I'll repeat that O O O to touch and feel very good velvet and help those are the 12 cranial nerves then moving on to the medulla this is the most a rooster a part of the extension of the spinal cord rooster just means in front of it doesn't necessarily mean anterior but rather in front of so it's going to be the rooster extension of the spinal cord and it's going to be consisting of these autonomic centers. So you can think of this as one of the controls of the automatic functions that you have in the body. So it's going to be controlling things like breathing. It's going to be controlling blood pressure. It's also going to be controlling reflexes such as swallowing, coughing, even vomiting. And a clinical correlation with this is that because the medulla is connected or rather an extension or rather in front of the spinal cord and individuals that are hung and you have that impact of the person being hung they may snap and actually fracture their bones in the cervical area and this can lead to compression of the medulla such that when the medulla is compressed then this person is not going to be controlling their breathing and remember that if breathing is not being controlled by the medulla and it becomes a voluntary thing it's very hard for you to think for you to breathe imagine if you had to think when you have to inhale and when you have to exhale you'd eventually get tired and you would eventually die so once the brainstem has been damaged or the medulla has been damaged then you're going to lose this autonomic functions then in addition to this there are some GSWs some gunshot wounds that may be in the neck area and may actually go and lodge into the medulla so they may actually affect the autonomic functions of this individual and they may be lethal to this individual Then the pons are a rooster to the medalla. So you first have the spinal cord followed by the medalla oblongata, then followed by the pons, then followed by the midbrain, just like that as you are ascending forward. Then... The pons are going to be participating in conjunction with the cerebellum to maintain posture as well as the also function in regulating breathing. As you learned in your prior academic year on the control of respiration, remember that respiration can be controlled both as a humoral and as well as a neural control. So the neural control, there are some centers that are present in the medulla. which are pretty much the dorsal respiratory group of neurons and the ventral respiratory group of neurons. Then in the pontine areas, you have the pontine centers that control the respiration, the apneustic center and the pneumotaxic center. Then the pons are going to be projecting information from the cerebral hemispheres to the cerebellum. Then moving on to the midbrain, so this is going to be in front of the pons and is going to be controlling eye movements. It also acts as a relay nuclei of auditory as well as visual systems. So it means that these centers are going to pass through the midbrain in order to reach, or these information from the auditory as well as the visual systems are going to be passing through the midbrain to reach the eye centers. Then moving on to the cerebellum, so take home message from the previous three structures, remember that they pretty much form the midbrain. So the... the brainstem rather not the midbrain the midbrain the pons and the medulla are going to be forming the brainstem then the cerebellum remember that cerebellum just simply means little brain so this is going to be attached to the brainstem and it's going to be lying dorsal so behind the pons and the medulla it functions in coordination of movements planning and execution of movements in conjunction with the basal ganglia it also function in maintenance of posture as well as coordination of head and eye movements Moving on to the diencephalon, we're going to discuss two predominant structures, the thalamus and the hypothalamus. So remember, the thalamus is just pretty much this relay center. You can think of it like a train station. If you're at a train station, there are people that are going to be coming to the train station. There are people that are going to be going to the train station. There are people that just drop off at the train station and just dilly-dally and wander around in the train station. So the thalamus is just like that. So it's going to be processing all the sensory information that's going towards the cerebral cortex. And almost all the motor information that's coming from the cerebral cortex to the brainstem into the spinal cord is going to be passing through the thalamus. So it is a very key center that's going to be functioning to relay both sensory as well as motor information. Then the hypothalamus, which is going to be lying ventral or anterior to the thalamus. You can think of this pretty much as a homeostasis center. Remember homeostasis is pretty much the maintenance of the constant internal environment. So it means that the hypothalamus is going to be also regulating certain functions that are enabling or that are allowing for homeostasis in the body. Things like regulation of body temperature, things like regulation of the food intake cycles, things like regulation of the sleep and wakefulness cycle, things like water balance, even endocrine functions. are going to be controlled by the hypothalamus because the hypothalamus controls the secretions of the glands that all the hormones that are produced by the anterior it also produces certain hormones that are released by the posterior pituitary gland Moving on to the cerebral hemispheres, these are going to be consisting of the cerebral cortex, which are the white matter divided into four predominant lobes, the deep nuclei, which are going to be pretty much the basal ganglia, which should be referred to as the basal nuclei, the hippocampus, as well as the amygdala. And remember that the cerebral hemispheres are pretty much going to be carrying out higher motor functions. They're going to be also carrying out higher functions, things like perception, things like cognition, thinking, things like memory and even emotions. So starting with the cerebral cortex, this is going to be having four predominant lobes, the frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe that are going to be separated by sulci and grooves. Then the cortex is going to be receiving and it's also going to be processing sensory information and it also integrates motor function. So remember that two integrative centers are present. the spinal cord which pretty much integrates most reflexes that need to be very quick as well as this the cerebral cortex which also integrates higher functions and also other reflexes then you have areas in the cerebral cortex you have primary secondary as well as tertiary sensory areas where the sensory information is going to be projecting to remember that the primary areas are going to be most directly and involved with the fewest number of Synapses. While the tertiary areas are going to be requiring most complex processing and they're going to be having a very very large number of synapses. But in essence, information that's coming from the sensory system are going to be projected into these areas so that the brain can process whatever you're perceiving from. this whole process and make sense of whatever you are getting from this sensory stimuli. Then the brain also has the motor areas, the premotor areas, the motor areas and the supplementary motor areas, which are pretty much going to be functioning in the movements of the body, which we will talk about in details later on. Then you also have association areas, which are going to integrate diverse information for one purpose or one action. Then moving on to the basal ganglia which should rightfully be called the basal nuclei. It's going to be consisting of traditionally the caudate nucleus, the putamen as well as the globus pallidus which is divided into a globus pallidus internus and a globus pallidus externus. Then the basal ganglia or basal nuclei is going to be receiving input from all the lobes of the cerebral cortex and it has projections. And it's going to be projecting its information via the thalamus to the frontal cortex to assist in regulating movements. So in essence, its function is to regulate movements. The hippocampus and the amygdala form a system that's known as the limbic system, which is very important in memory or emotions. For you to be able to remember this lecture, for you to get happy when you see my updates on the YouTube channel, or for you to get happy or sad when you remember someone that broke your heart. then the system has to work very well. So the hippocampus is essential for memory. While the amygdala is functioning in emotions, as well as the autonomic nervous system in conjunction with the hypothalamus. Here is a schematic again of the different parts that we talked about. The spinal cord over here, the medulla, the pons, the midbrain, the pituitary gland, the hypothalamus, the thalamus, the frontal lobe, the parietal lobe, the temporal lobe, the occipital lobe, and of course the cerebellum. These are the different parts of the nervous system. We shall talk about each of these parts during the course of these review lecture videos. Please tell a friend to tell a friend that we are actually covering neurophysiology topics. If you haven't yet subscribed to the channel, please subscribe to the channel. Drop a comment to show some support. Also, do not forget to hit the like button as well as the bell notification icon to be receiving notifications of such videos every time I post. My name is Dr. Moses Kazevu to Zambia and beyond.