[Music] high yield concept is to recall that we have somatotopic representations and in particular we have if you go with foot leg trunk arm and hand here we are in primary motor cortex in the purple we have leg and foot on the mesial wall medial surface trunk arm and hand sort of extending out and then face and mouth standing out laterally and further inferior as you go along that precentral gyrus then we have a pre-motor cortex which also has roughly somatotopic map foot leg hand arm face mouth and then on more on the um superior frontal gyrus supplementary motor areas we have leg arm face another somatotopic map and this is important to relate to if you have uh for instance a stroke that were to take out the aca the anterior cerebral artery recall that that is going to wrap up along this peri colossal region and have a peri colossal artery and a super marginal artery and is going to be supplying the territories that are mostly covering this leg foot region so if you have a patient who has a deficit uh with their left leg you might be thinking right mesial cortex and aca type stroke there versus if there's a mca stroke middle cerebral artery that's going to be covering more of this lateral surface and if everyone puts their hand out like so if this is going to be the distribution of the middle cerebral artery if you take your hand out put the palm of your head just hand just above your ear and wrap it over your head that is roughly the distribution of the mca middle cerebral artery and so with mca strokes as we heard about earlier you're going to have affecting more the face hand arm type of regions rather than the lower limbs and that's evident based on this rough topography of the brain okay so the motor cortices more specifically we have a new color scheme now but we have the motor cortex we have the central sulcus sorry indicated if you can see my cursor moving the red colored cortex is along the crease central which is where our primary motor cortex is located anterior to that are pre-motor cortex and then superior and mesial to that supplementary motor areas now these areas i'll discuss them each sort of individually but think of them as kind of working together but if you go back to dr dutany's lab and she were to open up your skull and put some electrodes in there and stimulate we're going to find that stimulation is going to elicit an awake behaving patient a non-preventable discrete motor movement of one or small group of muscles so if i were to stimulate in my right motor cortex right over the hand region zap stimulate my hands zap stimulate i'm going to say okay don't move my finger zap can't present it it's not preventable and and it's crossing so right side again controlling the left side of the body and all the movements are contralateral except force tongue masseter pharynx and some of the oral features and muscles now lesions to primary motor cortex initially will lead to a flaccid paralysis but then it's going to resolve quickly to hemiparesis mild spasticity and you're going to have most evident problems with fine skilled movements now one of the interesting things that dr jackson here back in the 1900s discovered is you can have individuals with seizures where a seizure may initiate say at the finger on the left hand and the seizure would start to cause the body to move and it would propagate up to the arm and the arm a good upper arm and then to the neck trunk region and then might actually cross over the other side of the body and uh it goes along this nice somatotopic map and that was one of the first clues that we had that there is a somatotopic organization in motor core it's a motor topic court organization and motor cortex and so that's referred to as a jacksonian seizure when you see someone who has a seizure where the spread of the epileptic motor spasticity spreads along a motor topic map like that and here is the homunculus i call them freddie i think it looks like a freddy if you were to take the amount of cortical real estate that is devoted to the various parts of the body we've got enormous representation of the tongue enormous representation of the hands because as we creatures are very much about using our hands and you can see the trunk and so forth is much less relative amount of cortical real estate devoted to control of motor movements that in that regard so that's our motor homunculus then in pre-motor cortex in the blue area up in here you can stimulate up in here thresholds are higher to get a movement but the movements are slower larger groups of muscles involved a lesion no paralysis or reflex changes unless you also take out some of the primary motor cortex if you take out both pre-motor and motor cortices you can get them the full-blown hemiparesis and then the so in general the pre-motor cortex is thought to be important for movements guided by external stimuli so if i want to reach out and grab my pen let's go ahead and initiate that movement boom i go and do that these areas are required for that initiation the third area supplementary motor area sma mostly in the uh purplish color here and on the mesial surface here's our paracentral lobule for instance as stimulation in these regions are going uh in this red sorry up in here stimulation is going to cause an assumption of posture so stimulate and you might have a full trunk type of movement turning the head and the trunk uh sometimes you can cause vocalizations uh you can even lead to speech arrests so there's some involvement some more fundamental elements of speech processing here or speech production rather and so this is thought to be more involved with planning and learning of complex intrinsically generated movements okay so here we have a coronal image a t2 and just looking at some functional landmarks for review here so in green we have our central sulcus and our paracentral lobule is going to be on either side of this a pre-central gyrus depicted between the green and the blue line and opposed central gyrus between the green and the red line here so those are running along the [Music] central sulcus going superior to inferior and immediately in front of that our frontal cortices are going to be running more anterior posterior and here this orange line is delineating for instance our superior frontal gyrus from our middle frontal gyrus in an image such as this another four important feature is the hand hook so it turns out so far this is our central sulcus on the right side and you can see this little omegas here the cortex often and many individuals is going to have an actual shape like this so you can actually surgically when you take off the skull plate you can sometimes see what is going to be this hand hook region of course as dr itani mentioned you want to make that keep that as eloquent cortex as possible since we are all about using our hands and this is often an anatomical feature that can be seen visibly of course better is to map it out using functional mri but if you don't have that option here you can see it in many individuals [Music] hey everyone ryan rad here from neurosurgerytraining.org if you like that video subscribe and donate to keep our content available for medical students across the world