Hello, hello my dear anatomy students! how are they? Welcome to another new anatomical video from your favorite anatomy channel easy anatomy by Juan José Sánchez.
Today I bring you the delivery of the generalities of the cranial nerves, all the cranial nerves are already developed in the channel, some in a single video because they are short, others in two, in three, even in four videos like the trigeminal nerve, well, yes already have more or less studied the cranial nerves, they should know that in a somewhat long cranial nerve. So here we are going to see a somewhat more general vision, we are going to see what the first one is about, very above, we are going to talk about its branches and routes, just name them and more or less know what each one is about, so that the logical and normal is that you watch this video before starting to see the cranial nerves in depth, but if you have already seen them in depth this serves as a review or if you are already advanced in it from the point of view of your career it will help you remember what principal of each part. Very well, let's start first by talking about what the cranial nerves are.
Remember that the cranial nerves are a set of thirteen pairs of nerves. It is the first thing that anyone who sees it would say, well, but I have read everywhere that there are twelve and Well, I had also read two sides that were twelve, but in certain anatomical texts that talk about cranial nerve number 13, which is the terminal nerve, I will talk about it. The latarjet is one of those that names and places a lot of emphasis on this 13th cranial pair.
So well, let's say in classical literature, old anatomy describes twelve cranial pairs so that there are 24 in total, that is, 1 on each side but Well, I want you to know that we are talking about 13 because the book that I used as a basis for the videos is cranial nerves, which is the latarjet. He talks about 13 cranial nerves, the important thing you have to know is that the cranial nerves are part of the peripheral nervous system, as we talked about in my video on generalities of the peripheral nervous system and they are not part of the central nervous system. What happens with the students is that since they see that the nerves emerge from the brain, they believe that it is part of the central nervous system, but if that is why the spinal nerves such as c1, c2, c3 also emerge from the central nervous system, in this case from the spinal cord.
spinal and that is not why we call it nerves part of the central nervous system, the peripheral nervous system will always derive from the central one. So these cranial nerves are like the spinal nerves but at the brain level, so how do we determine the cranial pairs because they all have a birth or arrival at brain structures, so they are going to leave the skull through some holes also called foramina or some They come out through fissures to be able to exit the skull or access it. Why?
Because there are some cranial nerves that come out with information, for example motor or parasympathetic, there are others that rather let's say enter the brain with information, for example the type of sensory vision. So in the end the cranial pairs all look for their respective nuclei, look, let's say from the third to the twelfth all have their nuclei at the level of the brain stem, the only two cranial pairs that do not have nuclei in the brain tract but rather are considered Extensions of the forebrain are the olfactory and the optic, that is, the first and second cranial nerves. Cranial nerve number 13 in this case, which is the terminal nerve, can also be considered as not having nuclei at the level of the brain stem.
Very good, although good, taking into account that this one is not very well described in general, look for the video, the video on the channel, the video of the terminal nerve, taking into account that it reaches the hypothalamic nucleus, they are not their respective nuclei, but hey, it is possible. be considered as having nuclei in the brain stem, however, well it is something that can be debated. So the cranial nerves can be of various types, there are some that are in charge of the motor part, we say that those efferent cranial pairs, there are others that have or that are in charge of the sensitive part, so we say that they are afferent type cranial pairs and there are others that are mixed, that is, They have motor information and sensory information, in fact there are special cranial nerves that also have great importance from the point of view of the autonomic nervous system, especially the parasympathetic one as I will name them later.
So well, let's look at each of these cranial pairs very briefly, but first don't let go of the video [Music] subscribe to the channel down here where you see that it says subscribe, click on it and well, we almost have 300 anatomical videos, there are 296 yes. I'm not wrong, so when you subscribe you stay subscribed to the more than 300 anatomical videos and well we continue doing it every day, if there is a video that you don't get, tell me in the comments, also write me from which country you are watching and What university are they writing to me about? So we had stayed with the cranial pairs, first we are going to talk about the classic 12 and then we talk about the cranial pairs, let's say number 13, which is really number 0 but so that you know that other cranial pairs, these cranial pairs, in this vision, it is an anterior vision of the brain stem.
They are some mixed from the most cephalic to the most caudal according to their site of emergence in the central nervous system, remember that there are some that are arriving and that have a sensitive nucleus inside the trunk brain and there are others that are emerging because they have a motor nucleus there, so we are going to start with the first cranial nerve, which is the olfactory nerve. Universally, the cranial nerves are listed with Roman numerals, so the first cranial nerve or olfactory nerve, right now Let's see their function a little more, we see that it is the most cephalic, it is considered an extension of the forebrain because it does not have nuclei of the trunk or brainstem, then we continue descending and we have the optic nerves, really here I am pointing out the optic tract because the optic nerve was cut here, but it is also practically an extension of the forebrain. They are the only two cranial pairs that do not have nuclei, I repeat in the brain stem the olfactory nerve and optic nerve, then we continue descending and we come from the lateral half lance and we have the oculomotor nerve , the common oculomotor nerve as a third pair cranial you see that this nerve is emerging at the level of the pontomesencephalic sulcus practically at the level of the interpedoncular space between the peduncles of the midbrain, something important that you have to know that there is also a real origin and an apparent origin with the cranial nerves, I explained it in each cranial nerve , but I'm going to make a single video talking about what the real and apparent origins of each cranial nerve are.
The real origin is the origin of the nucleus because, we are not going to see it in this image but we would have to see a schematized image of the nuclei, it is the origin where the fibers really originate or arrive, the apparent origin this is the place where apparently I see that he is emerging is where I begin to see. So this is the common oculomotor nerve, after the one lateral to it we find the trochlear nerve, it is the only nerve that comes from the posterior part of the brain stem and it also has the particularity that it is the only cranial nerve that decussates before emerging. What is here, then we are seeing the fibers that come from the nucleus of the trochlear nerve in this case, for example, the right one and here the one from the left that is seen to decussate and exit from the right side, this trochlear nerve also the so-called pathetic nerve because its paralysis causes a very particular characteristic in the eye that is called a pathetic look, that is why they gave it that name, then we have the trigeminal nerve, it is the most voluminous nerve and without a doubt the longest in branches, the richest in branches and that is why We dedicate four videos on the channel, to the trigeminal nerve you see that it has like two branches: the shortest one, the smallest is the motor branch and the thickest is the sensory branch, it is called trigeminal because it has three branches then we have the oculus nerve external motor we also call it the abductor of the eye or simply the abducens nerve or sixth cranial nerve, see that it begins to emerge at the level of the groove that is between the bridge and the medulla oblongata but we call it the medullopontine groove, okay?
because The medulla oblongata is also called the medulla oblongata and the pontine pontine. Then we have the facial nerve, it is also a nerve that has a very particular path, the seventh cranial nerve, see that the same continuous spinal groove emerges and is made up of two roots , one we call the facial nerve itself and the other we call the intermediate root. but together they make the facial nerve, lateral to it we have the nerve, before we call it the auditory nerve, today we call it the vestibulo-cochlear nerve because they are the separate components that make up a vestibular nerve and a cochlear nerve, it has to do with balance and hearing and we also call it the stratum acoustic nerve important fact then we have the ninth cranial nerve which is the glossopharyngeal nerve, these are cranial pairs from below that emerge in relation to the medulla oblongata, then below the glossopharyngeal nerve we have the tenth cranial nerve , since the vagus nerve is also called the pneumogastric and vagus nerve because it really has a very very very wandering path, very vagal like a vagus, it is throughout the body and reaches to the abdomen, it is the longest cranial nerve and yet it is long but it does not have as many branches as such and that is why we dedicated only two videos to it, below the vagus we have the spinal nerve, which is a very particular nerve also called the accessory nerve or the eleventh cranial nerve because it has one root, two roots and no nerve is formed by two roots, like one that comes from the spinal cord see spinal root and one that comes from the medulla oblongata which is called cranial root.
So it is the only one that has a root that comes from the spinal cord, very particular, and then finally the twelfth cranial nerve, which is the hypoglossal nerve, which you see is anterior to the ninth, tenth, and eleventh. So what does each cranial nerve do? Well, the olfactory nerve, for its part, is totally sensitive because what it does is simply capture odors, then the odors then go from the nasal cavity to the brain, the second cranial nerve optic nerve is totally sensitive, what it does is simply carry vision through sensory impulses.
of vision captured in the retina, are taken to the brain. Then we have the oculomotor nerves , the ones that move the eye, we have the third cranial nerve, which is the common oculomotor nerve, the fourth cranial nerve, which is the tochlear nerve, and the sixth cranial nerve, which is the abducens nerve, all of it. What they do is innervate extrinsic muscles of the eye, that is, in order to move the eye, the one that moves the most is the common motor oculus, trochlear and abducens each, let's say nine of a single muscle as such and common motor oculus moves 4 because between There is also the levator muscle of the upper eyelid and apart from the common motor oculus it carries parasympathetic fibers that also go to the eye, that is why the parasympathetic can easily act in the eye, for example, to be able to contract the pupil or also to innervate structures of the lens muscles, then has to do with accommodation.
Then the cranial parasympathetic nerve travels with the cranial nerves, it uses four cranial nerves, I'll tell you this at once before I forget to tell you , it uses the third cranial nerve which is the common oculomotor nerve, it uses the glossopharyngeal, it uses the vagus and it uses the facial nerve, those are the four cranial nerves that are of the parasympathetic type par excellence, the third, the seventh which is the facial, the ninth which is the glossopharyngeal, the tenth which is the vagus, very well then we have the fifth cranial nerve which It is the trigeminal nerve , very important because it has large components, a large sensory component for most of the sensitivity of the face, part of the pinna and the cavities, that is, most of the oral cavity, the gums, most of the ophthalmic cavity, most of the nasal cavity, which is then a major sensory component but also has motor fibers that go to the masticatory muscles, ok to the pterygoids, to the masseter, ok? for the temporal muscle, which are considered chewing muscles, then we have the facial, the seventh cranial nerve, which is responsible for the muscles of mimicry, that is, the muscles of facial expression, its great motor component, also other muscles but This in general and also has to do sensitively with the anterior two thirds of the tongue, taste and sensitivity and also its parasympathetic component goes to the saliva-producing glands, except the parotid, nothing else goes to the submandibular and sublingual. .
Then we have the vestibulo-cochlear nerve, well here with the edition cut the branch but the two branches are blue, they indicate that it is a totally sensitive nerve, see that so far the only mixed one , well, two mixed ones, we have talked about the trigeminal and the facial ones are mixed okay? 3rd, 4th and 6th motor 1st and 2nd sensory, this eighth cranial nerve, which is the vestibulo-cochlear nerve, is totally sensitive, the vestibular part is responsible for balance and the cochlear part is responsible for hearing, both structures are found in the inner ear, that is why We also called it the auditory nerve before. Then the glossopharyngeus, which is another of the mixed cranial nerves, is partly responsible for the sensitivity of the pharynx, the posterior third of the tongue, taste, also the posterior third of the tongue, and helps innervate certain muscles of the pharynx that, like It is the stylopharyngeal muscle and also helps the constrictors from a motor point of view.
This glossopharyngeal nerve is also responsible for innervating the parotid gland, which is important. Then we have the vagus nerve, another mixed nerve, I told you that it was called pneumogastric because in addition to innervating structures of the neck, motorically the muscles of the larynx, sensitively the larynx, the trachea, the esophagus, it innervates everything that is the gastrointestinal system. , it is said that practically up to the transverse colon all the parasympathetic innervation of that entire system is carried by the vagus nerve, it innervates the heart, cardiac plexus, pulmonary plexus, so see the importance of the vagus nerve, it innervates the auricle sensitively, the largest nerve without a doubt.
Then we have the eleventh cranial nerve, which is only motor, which is the spinal nerve, innervating the sternocleidomastoid and the trapezius, and finally the twelfth, which is the glossopharyngeal, which is also considered a motor nerve like the previous one that goes to the intrinsic and extrinsic muscles of the the tongue, that is why it is called hypoglossus below the tongue, I did not tell you that the spinal is called spinal because well it also has an origin from the spinal cord and we also call it accessory. Then, finally, the terminal nerve is a nerve that is difficult to find in images because it is said to involute in adults and its figures are actually quite microscopic. It is a nerve that has to do with the uptake of pheromones.
It is the function that is It gives him and also with the migration of sexual cells during the embryo, he will connect with the hypothalamus and where the gonadotropin-releasing producing cells are and it has its receptors at the level of the nasal mucosa, if you want to know more about it look for it on the channel. This was then all about the generalities of the cranial nerves, I have a video for you about the functional components so that you know when general visceral afferent, general visceral efferent, general somatic efferent, what entangles us all I have it quite summarized in a video and I have another one telling you about the real origins of the cranial nerves, this is undoubtedly a long topic, thank goodness we are already finishing it.
