YouTube Video Transcript

[Music] hello everyone welcome back to my channel it's been a long time uh so I am here with the session on the development of spinal cord it's very very important as far as uh ug or PG is concerned uh so we know the spinal cord uh is developed from the cordal end of the neural tube and neural tube is formed from the neurectoderm by the uh after the formation of the Nord which acts as a inducer of the neural tube so we know the neural tube will be formed by the folding and uh what happens after that uh we can see that this is the neural tube and in the beginning uh the tube the walls of the tube are very very thin and it is enclosing a cavity known as neurosin and later what happens is by around fifth week of development uh uh the epithelium or the walls of the neural tube will be redefined that is the first the lining of the neural uh tube is known as metrix and what happens to the metrix so you can see that this is the neuros seal the cavity and around the neuros seal first we can see that the wall of the neural tube which was very thin in the beginning develops as the metrix or the metrix Zone otherwise known as endal Zone and what is happening in the metrix two types of cells are formed within the metrix one is neuroblast and the other one is spongo blast so neuroblast gives rise to the neurons and the spongo blast will give rise to the neurog gal cells so the neurons and their supporting cells neuroglial cells now what happens to the neurons the neurons the cell bodies of the neurons will actually migrate just periphery to the The Matrix and they will be z uh they will be forming the mantle zone so it is the first zone is the metrix Zone then you have the mantle Zone just outer to it where the cell bodies of these migrating neurons are concentrated and that will be forming the gray matter of the spinal cord we know uh the spinal cord has got the gray matter inside and the white matter outside now what happens to the axons of these neurons the axons of these neurons will occupy the outer zone of the mantle Zone that is known as marginal zone so three zones are developed from the walls of the neural tube the innermost the metric zone or the endal Zone the outer just outer to it we have the mantle Zone where we have the cell bodies of the migrating neurons which forms the gray matter of the SP spinal cord and outer to it again outer to it we have the marginal Zone which is mainly occupied by the axons of these neurons which are concentrated in the mantle zone so uh so we have three zones for the developing spinal cord now one more thing which I would like to mention here is the remaining Matrix after the formation of the neuroblast and spongo blast will be forming the endal lining of the central Canal of spinal cord that is the fate of the metrix Zone uh now recent theories propose that uh there are no three zones like this and according to that Theory according to that recent Theory which is put forth after detailed study of the electron microscopy uh they say that the neural tube is made up of PL potent neuroepithelial cells PL potent means the cells which can give rise to any types of cells and it is just a pseudo stratified neuroepithelium and this layer is actually giving rise to neuroblast and their neurons will be seen the cell bodies of the neurons will be seen in the mtle zone and uh the nerve fibers will be seen in the marginal zone so ultimately uh the previous Theory the classical Theory comes into existence but the only difference is the according to the new Theory there is no Matrix Zone but they believe that it is just made up of a PL poent neuroepithelial cell and uh the different zones which we see are not actually zones they are actually the interkinetic migration of these neuroblast cells so that is just an additional point for the postgraduates now we can see that there is a dosal root ganglia which is connected to the spinal nerve emerging from the spinal cord and the central process the process of the dosal root ganga which is going to the spinal cord either Essence in the white matter that is the marginal zone or sometimes the synapse in the mantle zone of the concerned region so that is what happens for the central process of the dorsal root ganglia they either Ascend in the marginal Zone which is actually the white matter of the spinal cord or the synapse with the mantle Zone uh so this is uh just an overview of what happens to the walls of the neural tube simultaneously we should also consider about something about the functional column of the spinal cord how this gray matter is redefined as the functional columns when we uh think about the functional Columns of the spinal cord we have only General columns so that means there are some special columns in the brain stem uh that point you have to remember there are three special columns in the brain stem but when you think about the functional Columns of the spinal cord we have only General columns now when we take a crosssection we can see that the cavity is just like a slit so that the roof and floor are very thin plate and you call it as a roof plate and the floor plate and what happens to the lateral wall they are actually thickened the roof and floor are very thin whereas the lateral walls are thickened and there is a sulcus which separates this lateral wall into a doal lamina and a vental lamina that is how the spinal cord gets its shape okay so the sulcus limitans divides the lateral wall into a dosal lamina otherwise known as AAR lamina and the ventral lamina otherwise known as basil lamina now we know uh the dosal part of the spinal cord is actually concerned with the sensory and the ventral part is concerned with the motor so the functional columns are also like that in the doal OR AAR lamina you have the efen columns which are mainly sensory and in the ventral part or basil lamina we have the eeper columns or motor columns that is one important thing which you should be knowing now let's we we already mentioned that when you think about the spinal cord the functional columns we have only General columns now uh let's see what are the columns in the AAR or dosal lamina there are two general columns one is somatic General somatic eant the other one is General visceral e so General somatic eant is a dosal most and next to that you have the general visceral eant where will you get this General somatic eant this is seen throughout the spinal cord from the beginning of the spinal cord till the termination of the spinal cord but when you think about Al visceral efferent this column is confined to the thoracic region lumbar region and sacral region in the cervical region this column is not there uh so why you don't get this General visceral Leen column in the ciculation don't we have blood vessels and the viser there that is actually by the cranial nerves coming from the brain stem and uh we have special columns there now coming to the basil lamina B basil lamina is mainly eer e means motor going to the eector organ there also you have two columns one going to the viscer and blood vessels that is General visceral eant that will be lying closer to the general visceral eant and where will you get this General visceral Leen that again will be seen only in the thoracic Lumbar and sacral regions whereas the ventralmost column is known as general somatic eant and that is seen throughout the spinal cord and they Supply the skeletal muscles so uh what about the general somatic effect so once again I will just give a clear view the dosel or AAR lamina ventral or basal lamina all the functional Columns of the spinal cord are General in the brain stem only you have special columns now the doal is mainly sensory ventral is Main motor this much is clear isn't it sensory sensory means the sensations it they are mainly superficial and deep superficial Sensations are mainly cutaneous Sensations and deep Sensations are proprioception these are going through the general somatic Ean column which is there throughout the spinal cord now General visceral efferent that is carrying Sensations from the visera and blood vessels and they are not seen throughout the spinal cord but only confined to the thoracic Lumbar and sacral region coming to the ventral or motor that is eant so you have General visceral eant which is going to again the viscer and blood vessels which is lying closer to the general visceral efferent and it is not seen throughout the spinal cord it is seen only in the thoracic Lumbar and sacral region now the ventralmost is General somatic eant that is is actually motor and it is it is seen throughout the spinal cord and it is supplying the skeletal muscles so uh in a nutshell we know uh the spinal cord is developed from the cordal end of the neural tube after the neural tube is closed once we first and in the beginning it is very very thin lining then it is modified as zones the three zones according to the classical Theory metric Zone mandal Zone and marginal Zone and according to the new theory proposed it is nothing uh but the epithelium the C stratified neuroepithelium which is mainly plur poent and the ones which we see as mandalone and marginal zone are nothing but the different uh mode different times of migration of the neuroblast cells which are formed in the pseudostratified neuroepithelia uh and I will be doing one more session adjacent to this which includes uh the positioning of the spinal cord and the common congenital anomalies so keep watching uh and at this moment I would like to mention about the anas sculpt 2023 the details I will be putting in the uh section behind thank you