[Music] all right let's look at equilibrium Pathways so we looked at the pathways for the other special Senses we're going to do the same for the equilibrium so remember the hair cells right The receptors so the basic idea here is that hair cells detect that equilibrium sense and then the hair cells cause action potentials to be created or generated in neurons okay so you have neurons that synapse that connect with these hair cells the neurons that are synapse with hair cells are neurons that belong to your vestibular nerve all right vestibular nerve so vestibular nerve along with the clear nerve form IAL nerve 8 the vestibulo cocar nerve right and this is why we call this cranial nerve 8 the vestibulo cocar nerve because when it branches it branches into a vestibular nerve and a clear nerve so let's look here in the picture Okay so activating hair cells which cause Action potentials to form on these neurons so the neurons will transmit information through their Little Fibers okay and then so as the information is being transmitted through the neurons we get into this vestibular ganglia all right remember gangan is a mass of cell bodies right axons are really thin so the parts where the axons are at are very thin cell bodies are a lot larger part of the neuron a lot wider so when you have cell bodies it forms a these bulges here that we call ganglia so we transmit the information through the axons of these neurons into the vestibular ganglia and then out through the vestibular nerve okay so all these are like little branches right little branches of the vestibular nerve when they all come together and they all get bundled up as one unit that truly forms the vestibular nerve in full in truth and then there's part of the clear nerve coming from the CIA it's cut offs but then when that vestibular and clear nerve merge together it forms that cranial nerve 8 vestibulo cocar nerve okay all right so from there the vestibulo cocar nerve will transmit the signals the information to this part right here all right this is what's known as the vestibular nucleus right vestibular nucleus so whereas a gangan is a collection of cell bodies in the peripheral nervous system outside of the central nervous system a nucleus is a collection of cell bodies in the central nervous system right here okay so this is the brain stem right so we send those signals to the vestibular nucleus located here in the brain stem and then from there the vestibular nucleus with its synapses will will then send that information to several several different areas of the brain okay and spinal cord why do we need the vestibular nucleus to transmit that equilibrium information to many different places of the body of the brain of the spinal cord and then also out to to muscles because of what we need to do to deal with this sensory information this this equilibrium information so again look at these red lines notice how I did not highlight the all the other parts of the picture in blue right you just need to know for the pictures you need to know what's in this kind of blue highlighted stuff so functions of the of the vestibular nucleus right again the red arrows are showing you that it's sending signals out to lots of different areas so the vestibular nucleus is going to help integrate equilibrium information from both ears from both sides of the body it puts it together it's going to help relay information up to your cerebral cortex so that you're consciously aware of the position of your head and if your head is moving so you can feel that you're moving and you know closing your eyes you even know if your head's right side up upside down the position of your head the vestibular nucleus can relay information in the form of motor commands to muscles the head the neck the limbs and the eye so the reason we want to be able to send motor commands out to the Head muscles of the head neck Limbs and eye is to control muscles to help try to maintain the the position of your head to maintain your posture to maintain your balance and to be able to stay focused on whatever it is you're looking at okay right so let me say it really briefly again we want to control muscles in the head the neck your limbs and your eyes to try to maintain your sense of balance and your posture and to try to to be able to track or follow along something that that that you're looking at or if you're moving right if you're moving you want to be able to still look at what you're trying to focus your attention on okay so when you spin around in a circle okay the way that it works if you really think about it you might notice this but when you spin around in a circle what your eyes keep moving back and forth right so if you're if you're spinning in One Direction your eyes will jump ahead they'll look over to the side as far as they'll go and then as your head starts to move your eye will try to stay fixed on a a single point but at some point your head turns so much that your eyes moved all the way to the other side and that's as far as they'll go so then they jump ahead to look at the next Point as you're spinning around so the eyes go left and right back and forth back and forth back and forth when you're spinning around they jump ahead they lock in on a point they followed as much as they can go and then they jump ahead to the next Point as you're spinning okay that's normal that's fine that's okay but when you're eyes um sort of not twitch but when they when they move back and forth quickly when you're not spinning then that's what we call a nagus a nagus is an indicator that you might have some damage to that internal ear or you might have damaged to the brain stem itself where that information is sort of processed and then sent out to other parts of the body right so we look for nagus and nagus is sort of an abnormality that Clues Us in that there's a problem going on so if you watch this uh gentleman right here this is this is what I mean when I say in a stagis he's looking straight ahead so right even when you cover up one eye or the other you still get the the the nagas all right so this guy looks like he's not doing really well on the roller coaster remember that you know looking up or down is the same type of activity in the ear as is accelerating forwards or backwards or moving in in some type of line so we we we really need visual information visual stimuli to combine with your equilibrium information to really know which way you're moving and what direction so motion sickness occurs when your brain's receiving conflicting information it's getting one type of sense from your ear in equilibrium but it's getting a different type of sense from from what you see your your eyes so if you're on a boat in the middle of the ocean and you can't see the shore when you look straight ahead you don't see that you're moving up and down because you can't see anything out on the horizon right there's no land or anything it's just all water but your ear is telling you that you're moving up and down as the boat's rocking back and forth or up and down so this conflicting information your ears telling you that you're moving your eyes are are telling you that you're not moving this is what leads to motion sickness so the same thing can happen on a roller coaster or whatever or in a car if you're trying to read in a car and you get motion sickness right your ear is saying that you're moving but because you're reading or or looking at your phone then your eyes are saying that you're not moving because you're fixed on something that's not moving there are different there there are drugs that we can use to treat motion sickness Dramamine is like a common drug that people take to try to meet treat motion sickness and all these kinds of drugs do like Dramamine is it depresses or lowers the activity of that vestibular uh nucleus in the brain stem so if we can like lower the activity of that the vestibular nuclei in the brain stem the signals aren't strong getting up to your brain and you tend to not feel as sick you tend to not get motion sickness