✅ EMBRIOLOGÍA del SISTEMA NERVIOSO CENTRAL (Parte 2°) 🧠💥

Hello everyone! Welcome to my channel Today we are going to give Embryology of the Central Nervous System Second part In this video, we are going to touch on topics related to The Spinal Cord, the Differentiation of its Cells and the Positional Changes that this during its embryological development The wall of the newly closed neural tube consists of neural cells These extend over the thickness of the wall to form a pseudostratified epithelium, also thick, they are connected by junction complexes in the light During the neural sulcus phases and immediately after the tube is closed, cells divide

rapidly producing an increasing number of neuroepithelial cells, together they constitute the Neuroepithelial Layer or Neuroepithelium Once the neural tube is closed, Neuroepithelial Cells begin to create another type of cell characterized by a large round nucleus, with a pale nucleoplasm and a dark colored nucleolus Is about Primitive Nerve Cells or Neuroblasts these constitute the Cloak of the Mantle which is the area around the Neuroepithelial Layer which later will give rise to the Spinal Cord Gray Substance The outermost layer of the Spinal Cord, called the Marginal Layer contain nerve fibers that are born in Neuroblasts, in the

Mantle Layer As a consequence of myelination of the nerve fibers, this layer assumes a soft appearance and is therefore called the white matter of the Spinal Cord Due to the constant incorporation of Neuroblasts into the Mantle Layer, on both sides of the neural tube show ventral and dorsal thickening Ventral thickenings are the Basal Plates and they form the Motor Areas of the Spinal Cord The dorsal thickenings are the Wing Plates and form the Sensitive Areas a A longitudinal groove known as Limiting Groove marks the boundary between the two The dorsal and ventral portions of the

midline in the neural tube known as a ceiling plate and the floor plate respectively does not contain neuroblasts, essentially serve as pathways to the nerve fibers that cross from one side to the other In addition to the Ventral Motor Pole and of Dorsal Sensitive Pole, a group of neurons accumulates between the 2 areas to create a small Intermediate Pole, it contains neurons from the sympathetic portion of the Autonomous Nervous System and there is only the thoracic levels T-1 to T-2 and upper lumbar to L-2 or L-3 of the spinal cord Now we are going to

talk about Histological Differentiation Neuroblasts or Primitive Neurons occur only when neuroepithelial cells divide At the beginning, they have an extension central that extends to the light and here it receives the name of Transitory Dentrita but by migrating to the Mantle Cloak The extension disappears and the Neuroblasts become temporarily round and Apolar When differentiation proceeds 2 new cytoplasmic extensions appear on opposite sides of the cell body and they form a Bipolar Neuroblast At one end of the Cell, the extension soon produces a primitive axon and at the other extreme, shows various cytoplasmic arborizations What are the

Primitive Dendrites so here the cell It is renamed Multipolar Neuroblast and after further development, it becomes in the Adult Nerve Cell or Neuron Regarding Glial Cells Most of the primitive support cells, that is, the Glioblasts originate from Neuroepithelial Cells, after Neuroblast production ends Glioblasts migrate in the Neuroepithelial Layer to the Marginal and Mantle Layers, in the latter they differ in Protoplasmic Astrocytes and Fibrillar Astrocytes, both are located between the vessels and the neurons, where they fulfill supporting and metabolic functions The Oligodendroglia Cell is another type of support cells possibly from the Glioblasts, located mainly in

the Marginal Layer this forms myelin sheaths around the ascending and descending axons in the Marginal Layer During the 2nd half of development, a 3rd type of support cell appears in the Central Nervous System known as Microglia Cell it is very phagocytic and derives from the vascular mesenchyme when the blood vessels penetrate the nervous system when the neuroepithelial areas stop producing neuroblasts and glioblasts they differ in Ependymal Cells lining the central canal of the spinal cord During the elevation of the neural plate a group of cells appears on each edge of the neural folds, known as

neural crest cells, these are of ectodermal origin and extend along the neural tube They then migrate laterally and give rise to the Sensitive Ganglia or Dorsal Root Ganglia and other types of cells As development proceeds, the neuroblasts of the sensitive ganglia originate 2 extensions, the ones that grow in the center penetrate the dorsal portion of the neural tube, in the spinal cord they end in the dorsal horn or ascend through the Marginal Layer to one of the higher centers of the Brain Those extensions are known together as Dorsal Sensory Root of the Spinal Nerve Those

that grow on the periphery bind to fibers of the ventral motor root thus participating in training of the spinal nerve trunk In addition to creating Sensitive Ganglia Neural Crest cells are differ in sympathetic neuroblasts, Schwan cells, Pigment cells, Odontoblasts, Meninges and mesenchyme of the Pharyngeal Arches The motor fibers begin to appear during the 4th week, come from the neurons of the Basal Plates o Ventral Antlers of the Spinal Cord These fibers will come together and form the so-called Roots of the Ventral Nerves The roots of the Dorsal Nerves containing sensory fibers originate from neurons located

outside the Spinal Cord in the Dorsal Root Ganglia or spinal ganglia derived from Neural Crest Cells The extensions of their ganglia they form beams that penetrate in the Dorsal Antlers of the Spinal Cord Distal extensions join to the roots of the ventral nerves to form a spinal nerve Thus, the fiber of the dorsal root has a sensory innervation while the fibers of the ventral root have a motor innervation, so that the spinal nerves contain both sensory and motor fibers Almost immediately, the spinal nerves divide in Dorsal and Ventral Primary Branches containing as many motor and

sensory fibers The Primary Dorsal Branches innervate the dorsal axial musculature, vertebral joints and skin of the back And the Ventral Primary Branches innervate the extremities and the wall of the central body to form the great Nervous Plexuses and finally in reference to POSITIONAL CHANGES OF THE SPINAL CORD In the 3rd month of development, the spinal cord stretches throughout the embryo and the spinal nerves cross the intervertebral foramina at the level where it originates However with the passage of time the vertebral column and the dura lengthen faster than Neural Tube then the terminal end of the

spinal cord gradually goes to a higher level At birth this extreme is at the level of the 3rd lumbar vertebra Because of such disproportionate growth the dorsal and ventral roots of the spinal nerves move obliquely from the origin segment, in the spinal cord, up to the corresponding level of the spine There the appropriate roots unite to form the spinal nerves On the other hand, the dura remains attached to the vertebral column at the level of the coccyx In the adult, the spinal cord ends at level L2 or L3 while the Dural Sac, in the subarachnoid

space, extends to S2 At the end of the spinal cord a hilum-shaped extension of the Píamadre passes caudally, crosses the Duramadre and stretches up to the 1st vertebra of the coccyx This structure is called FILUM TERMINAL and marks the path of involution of the Spinal Cord, also providing support and the dorsal and ventral roots of the spinal nerves, below the terminal end of the medulla, in L2 - L3 together they make up the Ponytail And well, here we come this is the end of the second part I hope it has served you Thank you very

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