Cranial Nerves PDF

NOTE: Transcripts are made from the auto-generated Lecture Captions, so are not edited for grammar/spelling. Lecture 14 - Cranial Nerves Video 1 Introduction Welcome to the next online lecture. In this lecture we're going to be looking at the cranial nerves. So if you remember from earlier in th...

NOTE: Transcripts are made from the auto-generated Lecture Captions, so are not edited for grammar/spelling. Lecture 14 - Cranial Nerves Video 1 Introduction Welcome to the next online lecture. In this lecture we're going to be looking at the cranial nerves. So if you remember from earlier in the semester, cranial nerves are peripheral nerves that either originate or terminate in the brain. Many of these nerves have very special functions, including gathering sensory information from our special senses. So today we are going to be looking at the names and numbers of the cranial nerves, as well as their general functions and where they're located. So let's take a look. Slide 1 The material for this online lecture module can be found in chapter 13 of your textbook. We're going to be finishing chapter 13 now by looking at the cranial nerves. Slide 2 So the cranial nerves are part of the peripheral nervous system, but they arise directly from the brain and that's what differentiates them from the spinal nerves, or at least one thing that differentiates them from the spinal nerves. The cranial nerves have cell bodies or roots that originate in structures of the brain. There is one exception to this, and that's cranial nerve 11, the accessory nerve. It has some of its nerve roots stemming from the spinal cord and some that originate in the brainstem. Even though it does have roots in the spinal cord, it's still considered a cranial nerve, and I'll talk more about this particular nerve in a moment. We have 12 pairs of cranial nerves, and they are numbered using Roman numerals as you move from the anterior portion of the brain to the posterior portion of the brain. So it makes it easy to follow along with the numbering as you move from the anterior side to the posterior side. Of note, there is one region where the numbering is reverse and that involves cranial nerves 11 and 12. We can actually see this on an upcoming image. One pair of our cranial nerves arises from the cerebrum. One pair arises from the diencephalon. Nine pairs arise from the brainstem. And if you cross reference with our brainstem lecture from earlier, you'd be able to see all of the different cranial nerves that arise in the different regions of the brain stem. And finally, that one pair, that accessory nerve, technically arises from the spinal cord. Slide 3 The cranial nerves can be sensory only, motor only, or may have mixed functions. They may carry sensory information and this can be from the general senses such as temperature, pressure, pain. Or it can be one of the special senses like vision, hearing, balance, or taste. They can also have motor functions controlling skeletal muscles, or they can be part of the motor branch of the parasympathetic nervous system, where they're sending signals to smooth muscle, cardiac muscle or glands. Depending on the nerve, they may have a variety of different functions. On this slide we can see one of the many pneumonics that have been created to help students remember the names of all the cranial nerves as well as their functions. So this is just an example of that, and research actually shows that if you create your own pneumonics, that you'll actually have a better time remembering them. So you can try that out. The top pneumonic goes along with the names of the cranial nerves in the order that they're named from 1 to 12. The bottom, the functions are also matched up with the order of the cranial nerve. So S stands for sensory, N stands for motor, or B stands for both. So when you're moving your way down the cranial nerves, you'll see that the first nerve, the olfactory nerve, is a sensory nerve. So you can match up or create your own mnemonics to help you remember the names and numbers of the cranial nerves as well as their functions. Slide 4 So this is the image that I keep showing you on the title slide for chapter 13, with all the cranial nerves highlighted in yellow in this inferior view of the brain. But now I've also labeled all of the cranial nerves. You are responsible for knowing all of these labels and where the cranial nerves are originating. The first cranial nerve is the olfactory nerve. But in this image, we're pointing to a region called the olfactory bulb. Really the olfactory nerve is a 2 nerve system where we have the nerve fibers extending into the nasal cavity and then they synapse with this olfactory bulb region, which then transmits the information to our temporal lobe through the olfactory track. Cranial nerve number two is the optic nerve, so it's carrying visual information to the brain. We then have the oculomotor nerve, cranial nerve number three, the trochlear nerve number four, the trigeminal nerve number five, the abducens nerve number six, the facial nerve number seven, the vestibulocochlear nerve number eight, the glossopharyngeal nerve number nine, the vagus nerve number ten, the hypoglossal nerve number 12, and the accessory nerve number 11. So now you can actually see that these last two nerves have their numbers reversed when we're looking at nerves going from anterior to posterior. So those are the two that you need to remember are basically in the reverse order. Slide 5 So this is an actual anatomical specimen and you can see all these little pinpoints that I put in here are at the different nerves. So what I recommend doing is going through and looking at each of these little green pens and trying to decide which nerve each of these pins belong too. If you're interested in looking at some of these things and you have a copy of Connect, then you can see all of these same images in the AMP reveal tool. Slide 6 So what do you actually need to know from this lecture? Now you'll notice that some of the slides have a lot more details on the images and you're not expected to learn every single detail at this stage. So what I really want you to do is use table 13.5 along with the following slides to remember or learn the cranial nerve names, their number written in Roman numerals, whether they have motor function, sensory function, or both, and whether there's a parasympathetic component to that, and then their general function. So you don't need to know the exact muscles that they go to or every single component that they have an impact on. But I will summarize the general functions of each of the different nerves and that's about the level that I want you to know those things. You also need to know where the nerve originates. So some of those I've listed on the first slide there for you. And then we talked about many of the other ones in the brainstem lecture. I've also included several anatomical images that can help not only when you're going through the lab material for lab two, but they can also help you visualize where these nerves are coming out of the brain and where they actually go in the periphery. So let's take a little pause here and do some practice questions and then we'll come back and look at the cranial nerves. Video 2 Slide 7 The first cranial nerve is the olfactory nerve, which is a sensory only nerve and it's involved in our special sense of smell. As I mentioned before, it's actually a two neuron system where specialized receptors in the nasal cavity detect chemicals in the air and create an electrical signal. This signal is then brought through the roof of the nasal cavity through this bone and the holes in the bone called the cribriform plate, to a specialized region known as the olfactory bulb, where it can synapse with other neurons and then that signal is then carried to the temporal lobe of the brain via the olfactory tract. We will be looking more at the details of this particular nerve and how these specialized receptors work when we start to look at this special sense of smell in a couple of weeks. Slide 8 These are the anatomical images that I've added for you to help visualize these nerves. So in this particular image, we're looking at a sagittal view and you can see the olfactory nerve actually extends quite far and into where the roof of the nasal cavity, I like this view where the skeleton sort of overlaid so you can see where it is relative to the bones as well. So it actually extends quite far and then you can see those little fibrous structures, those would be the specialized neurons that are reaching through the bone into that nasal cavity. Slide 9 Cranial nerve two, or the optic nerve carries sensory information from our specialized sense of vision. So we're collecting information from the specialized receptors that are found in the back of the eye called the retina. It turns light information into electrical impulses. This signal then gets sent along the optic nerve, which exits on the posterior portion of the eyeball. And these two nerves joined together at a structure known as the optic chiasm. After they reach the optic chiasm, they then move through a region known as the optic tract towards the posterior part of the brain, known as the occipital lobe, where we have our visual cortex. We'll be talking a little bit more about this when we talk about our special sense of vision. Slide 10 So in this image you can see there's the eyeball relative to the eye socket of the bones and you can see that optic nerve exiting the posterior portion of the eyeball. And it's going to that region just anterior to the hypothalamus in the diencephalon. If you recall from the last lecture, I showed you that optic chiasm region and that was just right before the hypothalamus and that's where you can see that here. Slide 11 Cranial nerve number three is called the oculomotor nerve, and it has strictly motor functions. The main somatic motor function is controlling movements of the eyeball as well as the upper eyelid. So again, somatic motor means it's controlling skeletal muscles which are consciously controlled. So when we look down here at the image, we can see that the eyeball itself has 6 skeletal muscles that attach the outside surface of the eye, which is known as the sclera. These help to move your eye in a variety of direction. So left, right, up, down, and on a diagonal. So they are called the extrinsic muscles of the eye. This nerve controls four of these six muscles. It also controls some of the skeletal muscles that are involved in opening your upper eyelid. In addition, the oculomotor nerve also has a parasympathetic function and in this case, the nerve actually goes to the smooth muscle that's contained inside the eye. This smooth muscle controls the constriction of the pupil to change how much light is let into the eye. It also goes to the muscles that control the shape of the lens so that we can change the lens shape in order to focus on objects. Again, we'll be talking more about some of these specific structures when we get into this special sense of vision a little bit later. Another thing I just want to highlight is that even though we have only motor function for the oculomotor nerve, we technically have a small sensory component to all motor nerves. And that sensory component is for something called proprioception. So proprioception is basically giving your brain information about the tension and the position of different skeletal muscles and joints in your body. So in order for the brain and the cerebellum to make decisions about how to coordinate motor responses were constantly gathering some of that sensory information from these muscles, specifically the skeletal muscles. So whenever you see somatic motor control, know that there also is this proprioception sensory component, but technically it's only related to the muscle itself, so the nerve really only has technically motor function. Slide 12 So here we can see the oculomotor nerve. So how it's going to go to those muscles around the eye and then some of the muscles within the eye itself. Those are the intrinsic muscles of the eye, the ones that control the pupil diameter as well as the lens shape. But you can see this is also the first of the nerves that goes into the brainstem as we talked about previously, it goes into the midbrain region. Slide 13 Cranial nerve four is called the trochlear nerve. And like cranial nerve three, it's involved in the movement of the eyeball. It's a motor only nerve and in this particular instance, it's only innervating a single muscle associated with the movement of the eye. The nerve itself is actually named after this white structure right here that acts as a pulley to help redirect the line of pull of this particular muscle. The white structure is made of connective tissue and it's called the trochlear. So hence the name of the trochlear nerve. Slide 14 So again, you can see this is also going to portions of the brainstem, the midbrain region and you can see it's going to use specifically that one muscle that moves the eyeball. Slide 15 The fifth cranial nerve is the trigeminal nerve, and it has three branches, which contain functions for both sensory as well as motor. The three branches are the ophthalmic, which is sensory only, the maxillary, which is sensory only, and the mandibular which has sensory as well as motor. The trigeminal nerve is the only cranial nerve that carry sensory information from the skin. The rest of the skin of the body actually gets a sensory information from the spinal nerves. And you can see in this image that it covers these three regions of the face. So the ophthalmic branch is bringing information from the forehead, the upper skull, as well as the top part of the nose. The maxillary branch covers portions of the cheek and the upper lip. And the mandibular branch covers regions that are close to your ear as well as your lower jaw. This nerve also helps to avoid biting your tongue or your cheek when you're chewing your food. It's also responsible for the pain of many headaches. So if you can get rid of the trigeminal nerve, you can get rid of your headache, but of course, you won't be able to feel your face. That trigeminal nerve is also responsible for tooth pain because it has nerve endings that reach up into the regions of the tooth sockets. The motor function of the mandibular branch of the trigeminal nerve is for mastication and mastication is the anatomical word for chewing. So it's controlling the muscles that are involved in the chewing process. Slide 16 So this is a nice image depicting the trigeminal nerve and the different branches. So you can see there's the nerve itself coming from the brainstem. And then it's going to have regions hitting the skin of all of the face. So you can see some of these nerve branches are going to be internal, but the ones that go external are going on the outside of the skeleton here. Slide 17 So that's kind of a nice visual. And then the next image here is really showing the different divisions. So the mandibular is going to the lower region. It would be going to the lower jaw, teeth sockets, for example as well. The maxillary is going to the middle region or upper lip, also to the tooth sockets on the upper jaw. And the ophthalmic is going to regions of the nose, the forehead, and the upper portions of the skull. So let's take another pause here and try out some more practice questions. Video 3 Slide 18 The next cranial nerve is cranial nerve number six or the abducens nerve. It's a motor only nerve and this is the final nerve that's involved in the movement of the eyeball. Specifically, it's going to this lateral eye muscle which moves your eye laterally in the eye socket. Slide 19 So here again you can see the abducens nerve, it's starting in the brainstem and going out to that lateral side of the eyeball. Slide 20 Cranial nerves seven, the facial nerve, also has motor and sensory components. The sensory component of the facial nerve is involved in this special sense of taste, and in this case is innervating the anterior two thirds of the tongue, so it's receiving sensory information from that specific region of the tongue. For its motor function, it's involved in facial expressions. So what's happening here is it's controlling skeletal muscles that contract. And in most cases of the body, skeletal muscles are attached to bone, but in portions of the face, the skeletal muscle is attached to the skin and when these muscles contract, it helps to alter the expression on your face. It also has a component associated with the parasympathetic nervous system and this controls the glands of the salivary region as well as the lacrimal glands. So the salivary glands produce saliva and the lacrimal glands produce tears. Slide 21 So again, here's our anatomical specimen. You can see many of these nerve branches are going to the various muscles of the face and then you'll also see some of these nerves going to places like the salivary glands, as well as the lacrimal glands, which will produce the tears. Slide 22 Cranial nerve eight, the vestibulocochlear nerve is a sensory only cranial nerve and it's involved in our special sense of hearing and balance. This image shows it connecting to the structures of our inner ear. And we'll be talking more about the special senses in more detail when we get into hearing and balance, but essentially the vestibular cochlear nerve as made up of two nerves coming together. So there's the vestibular branch or the vestibular nerve, which sends signals associated with balance, and the cochlear nerve, which transmit signals from our special sense of hearing. So these two nerves actually come together to form the vestibulocochlear nerve. Slide 23 So again, this is quite a short nerve here. So it's going to be coming out of the brainstem and going right to those inner ear structures that are located beside it. So it kind of looks really short, but it would be projecting towards us in this image and that's why it looks so short. Slide 24 Cranial nerve number nine, the glossopharyngeal nerve, is both sensory and motor. So this one, unlike the facial nerve, is also involved in this special sense of taste. Except now the sensory information is coming from the posterior one third of the tongue. The motor function of this nerve is controlling the muscles involved in swallowing. The parasympathetic portion of this nerve innervates the parotid gland, which is involved in the production of saliva. Interestingly, this nerve also receives signals from the carotid body and carotid sinus, or specialized receptors found within our blood vessels, which are important for detecting changes in blood pressure, changes in blood pH, as well as blood gas changes or changes in the levels of oxygen and carbon dioxide. So many of these homeostatic functions that we talked about before are gathering information from these receptors found in the carotid body and the carotid sinus and bring this information back to the brain through the glossopharyngeal nerve. Slide 25 So again, you can see it's originating in the brainstem and then it's extending down to some of the muscles involved in swallowing, as well as some of the other structures that we talked about it just on the last slide. Slide 26 Cranial nerve number ten. The vagus nerve has quite a broad and extensive, complex set of structures that it enervates. It's both motor and sensory. The motor or skeletal muscle portions that it controls are muscles that are involved in the production of your voice, as well as swallowing. The sensory components of the vagus nerve are receiving information from a variety of different organs in both the thoracic cavity as well as the abdomen. In the thoracic cavity, it's connected to the lungs and the heart. And in the abdomen it's connected to the liver, the stomach, the spleen, the kidneys, the pancreas, the small intestine, and the colon. So it's very broad reaching this particular nerve. So it also monitors things like blood pressure, blood pH, and blood gases. Except now it's doing it in the region of the aorta, or it's gathering information from specialized receptors that are located in the aorta. It also was involved in parasympathetic control. So it receives sensory information from the organs, but it also sends a motor signals, or parasympathetic motor signals to a variety of organs found in both the thoracic and abdominal cavities. Those include the heart, the lungs, the digestive system, as well as the kidneys. So again, it's very broad reaching and we'll be talking about this nerve quite extensively, especially in term two of this course when we talk about the respiratory system, the cardiovascular system, the digestive system, and the urinary systems because it has quite a lot of control and monitoring of homeostasis for these various organs within the body. Slide 27 So again, you can't really see much of the vagus nerve here. You can see that it starting in the brainstem and then it extends down into the thoracic and abdominal cavities, but that's going to cut off in this image. Slide 28 Cranial nerve 11, the accessory nerve is one that I mentioned earlier that actually has some of its roots located in the spinal cord and others located in the medulla oblongata. One of the main jobs is motor function by controlling two of the neck muscles that are involved in moving your head. So these muscles are called the sternocleidomastoid muscle as well as the trapezius muscle. It's also involved in controlling some of the muscles associated with swallowing. The reason why it's called the accessory nerve is because it actually has some of its axons gathering or joining with the vagus nerve, and it helps participate in functions of the vagus nerve. Slide 29 So again, you can see it's originating in the brainstem and then it's extending back to some of those muscles involved in moving your head. Slide 30 Finally, we have cranial nerve 12, the hypoglossal nerve. This is a motor only nerve and it's involved in controlling muscles of speech and swallowing. So this would be muscles of the tongue as well as the throat. Slide 31 So in this image you can see again it's originating in the brain stem and it's extending down to those muscles in the tongue, as well as some of the muscles that will lead into the throat. So now that we've talked about all 12 of the cranial nerves, you may have noticed that some of the cranial nerves have similar functions like swallowing, for example. It might be helpful if you lump some of the cranial nerves together based on their common functions to help you remember what they do. Something else that was common was, for example, the nerves that control the movement of the eyeball. So when they have similar functions, if you can group them together, it will help with your understanding and help you remember what these different nerves are doing. So let's take a pause here and try out some more practice questions. Video 4 Conclusion So hopefully now you all have a pretty good idea of the 12 cranial nerves and their general functions. Remember to try and make your own pneumonic for the names of the cranial nerves as well as their general function. In the next online lecture, we're going to start to talk about the characteristics of our neuron that make it able to create an electrical signal. This is known as membrane potential. So until then, take care.