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Current time:0:00Total duration:8:02

Video transcript

in this video I'm going to talk about the brainstem brain stem and we briefly discussed the brain stem when we are talking about the structure of the nervous system as a whole so recall that the brainstem is right around here and if we look at our larger drawing of the central nervous system this is the brainstem right here and the brainstem connects basically all the parts of the nervous system together so the brainstem connects the cerebrum on top and it connects the spinal cord below and it connects the cerebellum which is behind the brainstem the brainstem also connects most of the cranial nerves you just write that over here cranial nerves so here's a different image of the brain looking at it from below so here's the cerebrum here's the cerebellum and here's the brainstem and all these little stringy things coming out are the cranial nerves and most of them are coming out of the brainstem so we'll come back to that in a minute but basically because the brainstem is connecting all these other parts of the nervous system together its Anatomy is complex there's a lot going on in the brainstem even though it's a fairly small structure it's just this little guy right here but it does a lot of things so let's take a look at some sections to look inside the brain stem so recall that this top part up here is called the midbrain this middle part is called the pons in this lower part is called the medulla so now let's take some sections so let's pretend we're cutting through the midbrain right here and we're going to look at it from the top so over here this would be a section of the midbrain midbrain and when we're looking down on it from the top it's kind of got these big parts that stick out the front of it and some little bumps on the back and don't worry about the names of any of those right now and then if we take a section through the pons so if we cut through the pons like this and we look down at the pons from the top this would be a view of a section of the pons let me just write that ponds and it's got this really big part that sticks out the front and then let's take a section here through the medulla and let's cut through the medulla and look at it from the top and that would be this guy right here so this is the medulla medulla or medulla I hear people say it both ways and the medulla has kind of a different shape so each each one of these three main divisions of the brainstem has a little bit of a different shape the inside of the brainstem has some similarities to the spinal cord particularly down low in the medulla where it's connecting to the spinal cord right here and similarly to the spinal cord most of the gray matter of the brainstem is on the inside and most of the white matter of the brain stem is on the outside but it's a lot more mixed together than it is in the spinal cord so there's kind of white gray matter more scattered about although most of the gray matters on the inside most of the white matters on the outside much of the brainstem gray matter or just these kind of distributed neurons that aren't in Nice discreet little places or bundles and we call this the reticular formation of the brainstem just all these these neuron somas scattered about - a lot of the gray matter inside the brainstem may just rape that over here the reticular formation ticular formation of the brainstem and this turns out to be a really important structure the reticular formation of the brainstem plays a big role in lots of autonomic functions autonomic and plays a big role in controlling things like circulation respiration and digestion some of our critical organ system functions and in addition to that for dissipating a lot of these lower functions of the nervous system the reticular formation sends lots of axons projecting up to the cerebrum up here and plays a major role in lots of the higher functions of the nervous system as well including cognition emotion and consciousness now a lot of the white matter that's passing through the brainstem is actually connecting the different parts of the nervous system so for example on these drawings over here which are kind of views from the front cutting through the nervous system like I've done here and what these drawings are showing or what we often call the long tracks long tracks and we call them that because there are collections of axons traveling a long distance through the central nervous system often connecting the cerebrum up top down to the spinal cord and they're just passing through the brainstem on their way to or from the spinal cord or the cerebrum and there are two big categories of long tracts that are really important passing through the brainstem so let me write two little Mark's here the first play a big role in the motor functions of the nervous system and these are actually the upper motor neurons so here in this drawing what they've shown is upper motor neurons starting way up here in the cerebrum and then passing down through the brainstem and mostly crossing over to the other side of the spinal cord where they're going to innervate lower motor neurons and here what they're showing in this drawing are somatosensory long tracts somatosensory and there are different kinds of somatosensory tracts carrying information to the nervous system but what this one's showing is somatosensory information coming up the spinal cord crossing and going up the brainstem and then going to the cerebrum on the other side from the body and so the brainstem is playing host to these long motor and somatosensory tracts that are carrying information up and down between the cerebrum and the spinal cord and as if all of that wasn't enough functions for the brainstem to be doing most of the cranial nerves as I mentioned are attached to the brainstem and the cranial nerves are doing all sorts of different things there are 12 pairs of these cranial nerves and most of them are attached to the brainstem let me just draw a few on my drawing over here but here's a much better drawing where they're showing the brainstem and and all of these little nerves coming out here are cranial nerves and there are 12 pairs of them most of which come out of the brainstem and the cranial nerves perform all sorts of functions including motor functions sensory functions and a number of different kinds of senses in addition to somatosensory functions there's things like hearing and taste and a number of automatic functions like reflexes and autonomic functions automatic functions and the cranial nerves are related to a lot of the gray matter inside of the brainstem because in addition to the reticular formation this kind of number of neuron somas that are scattered around there are collections of neuron somas that are nuclei that are discrete nuclei have been named and the cranial nerves are often carrying information away from these nuclei or into these nuclei depending on what functions they're performing so for example in this illustration over here we're kind of looking at the brain stem from the left side this is the front this is down and what they're showing are these nuclei have neuron somas and then axons are leaving the brainstem through cranial nerves to perform motor functions and then in this drawing they're showing sensory information coming in through cranial nerves to the brainstem two different nuclei in different parts of the brainstem now these cranial nerves are mostly performing these functions in the head and the neck let me just mark that in on our person over here but there are a few cranial nerves that actually travel from the brainstem all the way down into the body and perform functions in the trunk and in the limbs some examples of cranial nerve functions include sensation of the face and movements of the eyes face jaw and throat in addition to influencing organs like the heart and the intestines so there's a lot going on with the brainstem and I think I'll stop here and in later videos we can spend some more time going into some of the details of the different structures and the different functions of the brain stem but I just want to introduce it and give you a feel for all the different things it does