hey everyone ryan here and welcome back to our head and neck anatomy series this video will be all about the cranial nerves now this video will contain some new content but it'll also be a great recap to review all the various muscles that we've talked about up to this point so i want to start with a brief overview of the nervous system because there's a lot going on here and i'm trying to break this down into smaller pieces with this flow chart so this the nervous system can be broken down into two big components the central nervous system and the peripheral nervous system the central nervous system is composed of two parts the brain and the spinal cord the brain receives and processes sensory information it initiates responses it stores memories and generates thoughts and emotions the forebrain is the big part that's the cerebrum also the thalamus and the hypothalamus and it controls body temperature reproductive functions eating sleeping and display of emotions the midbrain is the small part it's only the top part of the brain stem and takes care of things like vision hearing motor control sleep and wakefulness alertness and a little bit of temperature regulation and the hindbrain is all the rest of the brain stem so that's the medulla pons and cerebellum and it supports vital bodily functions like breathing the spinal cord conducts signals to and from the brain basically the highway of neuronal signaling it also controls reflexes and that leaves the peripheral nervous system that's everything else that can be broken down into the sensory and the motor division we'll start with the sensory division and that's going to be carrying information from sensory organs to the central nervous system it's also called the afferent division afferent a-f-f-e-r-e-n-t means toward toward the central nervous system this can be broken down into somatic and visceral viscera meaning the internal organs each of these can be broken down one final step further into general and special so general somatic sensory is going to be things like uh we'll say touch pain pressure vibration temperature proprioception and the special somatic sensory things are going to be a vision hearing and balance and equilibrium and then in terms of visceral sensory that can also be broken down into general and special so general visceral sensory going to be things like stretch pain temperature and irritation in the viscera that also includes the sensation of hunger special visceral sensory are going to be things like taste and smell and then for the motor division that's where the central nervous system sends information to the muscles and glands this is also known as the efferent division e f f e r e n t or away from the central nervous system somatic is going to be the voluntary movements of skeletal muscle and the visceral motor division is basically the autonomic nervous system the autonomic nervous system is all those involuntary responses of smooth and cardiac muscle which are either fight or flight or rest and digest fight or flight is the sympathetic nervous system side rest and digest is the parasympathetic nervous system side i have a video on this in our pharmacology series diving into the differences between those two so all together you would enter this flow chart from the middle that would be the afferent pathway this peripheral nervous system would carry this information to the central nervous system via the spinal cord the brain would process that information and then it would go back out to the efferent or motor division to carry out either a voluntary or an involuntary action so that's basically the nervous system broken down in a few minutes now let's go through each cranial nerve one at a time so cranial nerve one is the olfactory nerve this one has special vince visceral sensory that's for smell so smell is also known as olfaction hence the name olfactory and then i'm going to include that flow chart that we just went through in each of these cranial nerves so you know which component they're responsible for so special visceral sensory is from the peripheral nervous system sensory visceral so the olfactory receptor neurons are these little tendrils here that collect information from the nasal cavity and traverse little holes in this cribriform plate that's in the ethmoid bone those tendrils join in the olfactory bulb which sends information along the olfactory tract where it eventually reaches the central nervous system at the temporal lobe so the primary olfactory cortex is located in the temporal lobe of the cerebral cortex of the forebrain where this information is processed the optic nerve is responsible for special somatic sensory for vision optic of course meaning eyes so the special somatic afferent or sensory is located right here on our flow chart so how is this information processed well the retina is at the back of the eye it's the start of this route it houses the photoreceptors it's going to carry this information via the optic nerve there's this crossover that happens we'll talk about this in just a little bit called the optic chiasma it continues as the optic tract and those optic tracks are going to eventually go to the lateral geniculate body or the nucleus which is a relay station of the thalamus that transmits information to the primary visual cortex which is located in the occipital lobe of the cerebral cortex of the forebrain where that information is processed so you might be asking what does this optic chiasma or chiasma do well this crossover here is so that whatever you see on the right in the right visual field ends up being processed on the left side of the brain and what you see on the left the left visual field is processed on the right side of the brain so a good way to think of this is if we drew an imaginary line between these two eyes so let's label everything we have the uh left side here we have the right side here that would be the left visual field the right visual field also the left eye and the right eye and then this would be the left side of the brain and the right side of the brain back here okay so this half of the retina is going to see the right visual field this half of the retina is going to see the right visual field i'm going to change colors for the left side this part of the retina is going to see the left visual field this part of the retina is going to see the left visual field now if we track the optic nerve and the optic tract back to the brain that part is going to go to the right side of the brain and this part is going to cross over thanks to the chiasma also to the right side of the brain so what's being processed from the left visual field goes to the right side of the brain so to the opposite side for the right same thing this is going to cross over to the left side of the brain this one's going to stay on the left side of the brain so everything looking at the right visual field gets processed on the left side of the brain so it's always to the opposite side of the brain which is pretty cool that's the function of the optic chiasma so how could this appear on a board exam question well for example what would happen to someone's vision if the left optic nerve was severed well if this was severed there's still left field peripheral vision coming from the right eye reaching the occipital lobe so the only way to sever all left field vision would be to sever the right optic tract that's the only way if you go behind the optic chiasma to cut off an entire half of your visual field also what i see pop up on the board exam all the time is that women are better at shade matching in terms of composite and crowns due to having more cone cells the rot their rod cells and cone cells located in the retina cone cells are more susceptible or more sensitive to color so next we have the oculomotor nerve cranial nerve 3. this one supplies somatic motor to the extra ocular muscles so these are the superior rectus inferior rectus medial rectus and inferior oblique we can also throw in the levator palpable superioris there are two other extra ocular muscles that the two of the next cranial nerves that we'll talk about are responsible for innervating instead the oculomotor nerve also supplies parasympathetic nervous system fibers to smooth muscle associated with pupil constriction we actually went over this in our last video on the eye muscles so the signal originates at the edinger westfall nucleus in the midbrain and then the neuron synapses close to the eye of the ciliary ganglion and then tells the pupil to constrict via the iris or pupillary sphincter muscle and the ciliary muscle is responsible for focusing the lens so that's the pathway this parasympathetic nervous system pathway for pupil constriction and that's the parasympathetic nervous system at work so the trochlear nerve is cranial nerve four and it supplies somatic motor to the superior oblique muscle like we talked about in the last video this one is the one that wraps around that trochlea the ligamentous slang of tissue hence why it's called the trochlear nerve it's the only cranial nerve that arises from the dorsal side of the brain stem just a fun fact there and how we remember this is our little uh memory tool so4 lr6 so4 stands for superior oblique cranial nerve 4. all right next we have the trigeminal nerve which is a massive nerve this is one we absolutely have to know as dentists the sensory information from the orofacial region is carried almost exclusively by the trigeminal nerve this also includes touch from the anterior two-thirds of the tongue it also supplies somatic motor to those all-important muscles of mastication the trigeminal nerve is broken up into three divisions we'll go over those briefly now the ophthalmic division is v1 here are some of the branches it has the frontal nerve supplies the forehead and i remember f and f this one further breaks down to the super orbital above the eye and supratrochlear which innervates the skin above the medial canthus again remember trochlea is that ligamentous sling of tissue located on the medial orbit that the superior oblique muscle hooks around so this nerve passes near the trochlea which feeds the medial corner of the eye so that's how i remember the trochlear and medial connection the lacro lacrimal nerve innervates the skin above the lateral canthus that's where that lacrimal gland is located on the lateral the superior lateral portion of the eye that's how i remember that you can also remember l and l and the nasociliary nerve supplies the nose as well as the eye long ciliary goes to the eye posterior ethmoid anterior ethmoid which innervates the external nasal region and the infratrochlear goes to skin adjacent to the medial canthus same reasoning here trochlear and medial line up together the maxillary division is v2 this one enters the targo palatine fossa via the foramen rotundum that we talked about in our fossa video and its branches exit this fossa by several different routes you can go back to our fossa video make sure you watch that one if you haven't already we talk about all these different different nerves and in fact all the nerves we talked about in that video are on this slide because they're all branches of v2 which makes its home in that pterygopalatine fossa so that's a pretty cool connection the sphenopalatine nerve exits via the sphenopalatine foramen and it later becomes the nasopalatine nerve that exits the incisive canal to feed the primary palate area the pharyngeal nerve exits via the pharyngeal canal these are all openings from the pterygopalatine fossa the greater and lesser palatine nerves exit via the greater palatine canal and then their associated foramina that line up the greater and lesser palatine foramen the psa posterior superior alveolar nerve exits via the pterygomaxillary fissure and it pierces the posterior maxilla maxilla above the tuberosity this one supplies the molars and the associated buccal soft tissue the zygomatic nerve has two little branches there and the infraorbital nerve exits via the inferior orbital fissure the zygomatic nerve also exits via that same opening and this one branches off into the middle and the anterior superior alveolar nerves so the middle supplies the premolars and oftentimes the mesial buccal aspect of the first molar and the associated buccal soft tissue the anterior one supplies the anterior teeth on one side of the mouth and the associated labial soft tissue finally we have the mandibular division v3 this one's the the one that's supplying all those muscles of mastication that we talk so much about the auriculo temporal nerve is an important one it supplies sensory information from the temporomandibular joint as well as the anterior oracle of the ear just a little bit there it also splits around the middle meningeal artery that's just like another little fun fact uh it also supplies the this part of the side of the head that's overlying the anterior temporal bone we have the long buccal nerve which supplies sensory information from the buccal gingiva of the mandibular molars the lingual nerve of v3 is that one responsible for sensory information from the anterior two-thirds of the tongue as well as floor of the mouth and lingual gingiva this one is joined by the chordae tympani of cranial nerve seven for special sensation of the same region of the tongue we'll talk about that when we get to the facial nerve the inferior alveolar nerve is a really really important nerve it also passes between the the ramus of the mandible and the sphenomandibular ligament in the pterygomandibular space and it's supplying sensory information from all the mandibular teeth it has a bunch of branches the mental branch exits down here via the mental foramen and it supplies facial gingiva of the anterior teeth lower lip and the chin the incisive branch continues within that mandibular canal so it doesn't exit and it supplies the anterior tooth pulps the milo hyoid branch actually splits off before the ian enters the mandibular frame and it splits off in a lingual direction it supplies motor information to the myelohyde muscle but it also may supply accessory sensory innervation to the mandibular molars oftentimes when you can't get somebody numb sometimes if you give a local infiltration on the lingual surface you can get that mylohyoid branch which may be supplying some sensory information to those molars and lastly we have the medial pterygoid nerve this applies motor information to the medial pterygoid muscle of course but it also is responsible for supplying the two tensor muscles tensor valley palatini and the tensor tympani the abducens nerve is cranial nerve six this one is nice and easy the only thing it does is supply somatic motor to the lateral rectus and this completes our fun little memory tool so4 superior oblique cranial nerve 4 lr6 lateral rectus cranial nerve six all right the facial nerve is our other really big nerve that we have to be familiar with this one carries sensory information from the ear tongue and palate so what's specifically doing is getting a somatic sensory information from the ear via the posterior auricular nerve that nerve also powers the intrinsic and extrinsic auricular muscles that we talked about two videos ago visceral sensory information is coming from the anterior two-thirds of the tongue that's taste via the quarter tympani and also taste from the palette believe it or not via palatine nerve branches we're getting somatic motor to the muscles of facial expression that's a massive function of the facial nerve and the chordae tympani is also involved in supplying parasympathetic nervous system information to the salivary glands like the submandibular and the sublingual there's also the greater petrosal nerve of the facial nerve which supplies parasympathetic nervous system information to accessory glands we're going to talk much more about these glands in detail in the next video which will be on salivary glands so a little bit more on the cord of tympani this is a cool little nerve and it passes through the middle ear and exits into the infra-temporal fossa through the petro-tympanic fissure it's this little slit in the temporal bone that runs from the temporomandibular joint to the tympanic cavity the main trunk of the facial nerve actually enters the parotid gland and it branches within it has these five main branches and the fun little memory tool here is two zanzibar by motor car each of those letters corresponding to the first letter of each of these five branches this is the temporal branch the zygomatic branch the buccal branch the mandibular branch and the cervical branch of the facial nerve bell's palsy is another thing that comes up as a high-yield fact with the facial nerve it's idiopathic we don't always know what causes it usually temporary paralysis of the muscles of facial expression on the affected side so you might see a drooping lip something to that effect and similar symptoms can arise from a traumatic injury to the nerve a stroke or in rare cases an incorrectly placed mandibular block all right vestibular cochlear nerve is the cranial nerve eight it is involved in special somatic sensory information for hearing and balance the vestibular branch detects balance via the utricle and the saccule those are part of the balancing system within the inner ear and the cochlea detects hearing both of those branches travel through the internal auditory meatus the glossopharyngeal nerve is cranial nerve nine this one's responsible for both touch and taste from the posterior third of the tongue via the lingual branch the lingual branch by the way is not to be confused with the lingual nerve of cranial nerve five which supplies touch to the anterior two-thirds of the tongue the glossopharyngeal nerve is responsible for triggering the cough or gag reflex which is most noticeable if you're taking an upper alginate impression believe me the uh it also supplies somatic information somatic motor information to the stylopharyngeus muscle it's actually the only muscle that it supplies as you can tell from this flow chart there's a lot going on here so we also have the autonomic nervous system at work with this cranial nerve so let's talk about the carotid sinus briefly the carotid sinus is also known as the carotid bulb and it's this dilated structure at the bifurcation of the common carotid artery into the internal and external branches so this dilatation contains a change containing some baroreceptors or stretch receptors which are sensitive to pressure changes in the arterial blood pressure so it's actually able to respond to changes in blood pressure in order to help regulate it like when someone stands up from lying down for a long time this is known as the baro reflex and it's carried by the glossopharyngeal nerve specifically herring's nerve of cranial nerve nine we also have the carotid body which is very close by and that's a small cluster of chemoreceptors or chemical receptors also at this bifurcation this bifurcation by the way is usually located between c3 and c4 of the spine so the carotid body detects changes in the chemical composition of arterial blood that's flowing through it mainly the partial pressure of oxygen but also carbon dioxide ph and temperature and it sends information to the brain via cranial nerve nine in order to help regulate blood oxygen levels the glossopharyngeal nerve lastly also has this lesser petrosal nerve just like the facial nerve had the greater petrosal nerve this one's also going to salivary glands but the parotid gland in this case again we'll talk more about the salivary glands in the next video all right the vagus nerve also has quite a bit going on here and it's going to uh carry sensory information from the laryngeal mucosa below the vocal cords it's going to supply visceral sensory and motor innervation from and to the heart lungs and the digestive tract so it plays a role in regulating major body organs it supply somatic motor information to most pharynx larynx and soft palate muscles we had videos on all of those earlier on in the series the big exceptions if you remember are the stylopharyngeal muscle that's cranial nerve nine we just talked about that as well as the tensor belly palatini we also talked about that that's supplied by v3 the vagus nerve also carries the motor end of the cough or gag reflex so the glossopharyngeal nerve is going to detect the gag and the vagus is going to contract the posterior pharynx muscles to initiate the cough just like we had the carotid body we also have aortic bodies these are similar to the carotid body but located along the aortic arch and there are basically small clusters of both chemoreceptors and baroreceptors that together detect changes in blood pressure oxygen carbon dioxide and ph of the arterial blood that's flowing past them and this one's innervated again by the vagus nerve the spinal accessory nerve is cranial nerve 11 this one's also pretty simple it's just supplying somatic motor to the sternocleidomastoid and the trapezius muscles interestingly the spinal root originates from c1 to c5 and it ascends into the skull via the foramen magnum and then exits via the jugular foramen so two big skull foramina that we talked about and the last but not least the hypoglossal nerve cranial nerve 12. this one supplies somatic motor information to the tongue muscles so the genioglossus which is the majority of the tongue the hyoglossus and the styloglossus the only exception is the palatoglossus which is innervated instead by the vagus nerve all right so that's it for this video on the cranial nerves i hope you learned a lot and thank you so much for watching please like this video if you enjoyed it and subscribe to this channel for more on dentistry if you're interested in supporting this 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