 Hello friends, let us see what is upper motor neuron and lower motor neuron lesion popularly known as the UMN and element lesion and how to identify the site of injury in case of this upper motor neuron or lower motor neuron lesion. So, for understanding this UMN and element lesion, we have to first understand the pyramidal tract. So, let us draw a simplified version of the pyramidal tract. So, this is just depicting two halves of the body. So, this is left side and this is right side. So, pyramidal tract neuron arises from the motor cortex. From the motor cortex via the internal capsule, it reaches to the medulla and what happens that at the level of the medulla there is crossing over this neuron and then it descends in the spinal cord until it reaches the site where the neuron has to leave the spinal cord. So, at that level, it synapses with another neuron which we call as alpha motor neuron. So, this is alpha motor neuron and this alpha motor neuron actually supplies the muscle. So, this is a simplified scheme for the pyramidal tract. So, we have drawn only one pathway where the neuron supplying one particular muscles are going. But remember here that the neurons which supply different muscles leave at different levels of the spinal cord. So, this is very crucial in understanding UMN and element lesion. So, what is actually UMN and element? See this portion from the spinal cord at the level where the neuron is synapsing to the muscle this is known as lower motor neuron. And if there is an injury which affects from the spinal cord where it is synapsing, remember I am saying where it is synapsing right to the level of the muscle it is known as lower motor neuron lesion. The rest from motor cortex to the spinal cord it is known as upper motor neuron and any injury which affects the neuron from motor cortex to this level is known as upper motor neuron lesion. Now, one thing we can understand from this diagram that if the injury is anywhere after crossing over that means here, here, here or here, we will get the same side signs and symptoms see if you trace the pathway it is on the same side. So, if there is a left sided injury of the spinal cord so, since the fibers are supplying on the same side of the body so, there will be left sided muscle weakness or left sided paralysis will be there. However, if the injury is in the medulla internal capsule or motor cortex the fibers which are coming there will cross over. So, if there is an injury on the right side of the motor cortex internal capsule or the medulla then only there will be left side weakness. So, in case there is right side weakness that means the left sided motor cortex internal capsule and medulla are affected. So, this is a very clear in this diagram it can be easily understood just by tracing the pathway. Okay, now further we will go by looking at a case and understanding how if the injury is at a motor cortex or at different levels how there will be presentation of the patient. So, we will see just one case and we will understand it. So, this is the case now, if we see the crucial features of this case you see on examination of a patient with muscle weakness so, the patient is having the muscle weakness it was found that on the right side of the body. So, we have signs on the right side of the body features of element injury at the level of L1. Okay, so, element injury at the level of L1 is there. Features of UMN injury are present below the level of L1. So, L1 here means the various levels of the spinal cord. So, lumbar region of the spinal cord first lumbar region is we are talking as L1 and the features as such what are the features of human element injury that we are not going to discuss in this video we are discussing how to identify the site of injury for the features there will be another video. Okay, anyway so, the muscles above L1 were normal. So, there is L1 at the site of L1 the neurons which are coming out of L1 we have element lesion below L1 that is L2 L3 everywhere we have UMN features and above L1 we have normal no injuries there. So, can we identify the site of injury just by this information let us see. So, let us once again see that pyramidal tract. So, this is a pyramidal tract now remember that I told you that neurons different neurons leave the spinal cord at different levels. So, the neurons which are supplying the leg muscles or the quadriceps they will leave in the lumbar region and that too also at different levels and the neurons supplying the arm the forearm they are leaving at the thoracic level. So, that should be very clear that different neurons are living at different levels. So, let us draw one other neuron just to understand this. So, there is another neuron which will draw which will leave at some maybe earlier level. So, here it is synapsing in the spinal cord and it is leaving and supplying the muscles different muscles. Okay, now our patient we said that if he is having right sided weakness. So, this sided weakness the patient is having. Now, let us see if there is injury of motor cortex internal capsule or medulla. Can you tell that whether it is a UMN injury or LMN injury from our previous discussion remember that anything above that synapse it is a UMN lesion and from the synapse to the muscle it is the lower motor neuron. So, if the injury is here suppose you see that it is the upper motor neuron fibers all the upper motor neuron fibers are affected no lower motor neuron fiber is affected. So, in this case we will not get any features of lower motor neuron lesion. So, anywhere injuries from here to here we will get only UMN lesion. So, does our patient has only UMN features the patient has both UMN and LMN lesion. So, definitely the injury is not in these three areas and also if you say that if right sided injury of these areas is there then there will be left side the signs and symptoms will be on the left side. Anyways, so that is one thing. So, that means injury is somewhere at the level of the spinal cord. Now, we have drawn two levels let us see let us put these levels as say suppose L1 because we are here L1 is our area of interest and L2 below and above will be our thoracic 12 level. Now, suppose the injury is somewhere here say at the level of the L1. Now, can you tell which type of injury it is? Is it LMN, UMN? Obviously, when you will see this the first answer which will come to your mind oh it is at the level of the synapse. So, it is a LMN lesion correct it is a LMN lesion. So, here we are getting LMN lesion, but you see the other neuron the other neuron which is leaving below L1 it is not synapsing at the level of L1 it is synapsing at the level of the L2. So, for this path where this upper motor neuron is injured see here this is injured upper motor neuron for L1 level it is the lower motor neuron which is injured. So, for this it is upper motor neuron. So, see at the level of L1 we are getting LMN features below the level of L1 because all the neurons which will be going below this they will be synapsing somewhere below only right. So, all of these will be upper motor neuron there upper motor neuron will be injured. So, below the level of L1 we are getting UMN features. So, that is below the level you are we are getting UMN at the level we are getting LMN and above the level you see what is happening above the level the neuron would have synapse somewhere here and would have left the spinal cord see there is no injury injury is below. So, this neuron is not injured this pathway is not injured. So, these are we are not getting any signs and symptoms above the level of the lesion right. So, that is our patient is showing. So, definitely we have figured it out that injury as at the level of L1 and Z at spinal cord in simple terms we can say that whenever we are getting both LMN and UMN features injuries at the level of the spinal cord and the level at which LMN features are there that is the level of the injury understood okay fine. So, this much we have figured out but which side of the spinal cord is it left side or right side. So, you can trace this here we have drawn everything on the left side. So, you trace it you see we will get left sided paralysis in this case or left sided muscle weakness in this sense. So, if the injury is in the spinal cord we will get the same sided features same sided muscle weakness. So, our patient had the right sided features. So, that means the other side fibers which are coming from the left side of the motor cortex they are affected right. So, injury is in the right side of the spinal cord because we are getting right sided weakness. So, this is our patient. So, this is the site of injury. So, hopefully this video might have helped you to identify what is the site of injury in case of muscle weakness if it is at the level of the motor cortex internal capsule or medulla we will get opposite side muscle weakness or paralysis and that too it will be only upper motor neuron type. But if the injury is at the level of the spinal cord we will get both upper motor neuron and lower motor neuron features. Lower motor neuron features at the level of the lesion and below the level of the lesion there will be upper motor neuron lesions. Okay. Thanks for watching the video. If you liked it do like and share the video and don't forget to subscribe to the channel Physiology Open. Thank you.