✔️📚Short, Practical and Simple
EmbryologyLangman #Medicine #Veterinary #Kinesiology #Biology
Bibliography:
- Netter Atlas of Embriology
- Langman Embryology 13th Edition
- Moore 8th Edition Embryology
- Human embryology and developmental biology Carlson 4th edition
- Human Embryology Armando Valdez
SPINAL CORD
Neuroepithelial, mantle and marginal layers The wall of the newly closed neural tube is made up of neuroepithelial cells. These cells are distributed throughout the thickness of the wall and form a thick pseudo-stratified epithelium. They are connected by means of junction complexes in the lumen. During the neural groove stage and immediately after tube closure, they divide rapidly and increasingly produce neuroepithelial cells. Collectively they constitute the neuroepithelial layer or neuroepithelium.
Histological differentiation
Neural cells
Neuroblasts, or primitive nerve cells, are formed exclusively by the division of neuroepithelial cells. Initially, they have a central process that extends into the lumen (transient dendrite), but when they migrate into the mantle layer, this process disappears and the neuroblasts for some period are round and apolar. As differentiation progresses, two new cytoplasmic processes appear on opposite sides of the cell body and a bipolar neuroblast forms. The process at one end of the cells rapidly elongates to form the primitive axon, while the process at the other end develops a series of cytoplasmic arborizations, the primitive dendrites. This cell then
Known as a multipolar neuroblast, it develops into an adult nerve cell or neuron during later development.
Glial cells
Most of the primitive support cells, the glioblasts, are formed from neuroepithelial cells after the production of neuroblasts ceases. Glioblasts migrate from the neuroepithelial layer to the mantle and marginal layers. In the mantle layer they differ into protoplasmic astrocytes and fibrillar astrocytes. These cells are lodged between the blood vessels and neurons, where they support and perform metabolic functions.
Another type of support cell that may be derived from glioblasts is the oligodendrocyte. Identified primarily in the marginal layer, this cell forms myelin sheaths around the ascending and descending axons of the marginal layer.
During the second half of the development process, a third type of supporting cell appears in the CNS, the microglial cell. This type of cell with great phagocytic capacity is formed from the vascular mesenchyme when the blood vessels grow into the nervous system. Once neuroepithelial cells stop producing neuroblasts and glioblasts, they differentiate into ependymal cells that line the central canal of the spinal cord.
Changes in position of the spinal cord
In the third month of development, the spinal cord extends the entire length of the embryo, and the spinal nerves pass through the intervertebral foramina at their level of origin. Despite this, over time the spine and dura mater elongate more rapidly than the neural tube, and the terminal end of the spinal cord gradually shifts to a higher level. At birth, this end is located at the level of the third lumbar vertebra. As a consequence of this disproportionate growth, the dorsal and ventral roots of the spinal nerves are obliquely oriented from their origin segment in the spinal cord to the
corresponding level of the vertebral column, in which the corresponding roots are united to constitute the spinal nerves. The dura remains inserted into the spine at the coccygeal level.
In the adult, the spinal cord ends between the level of L2 and L3, while the dural sac and the subarachnoid space extend to S2. At the lower end of the spinal cord, an extension formed by a pia mater and similar to a thread extends in a caudal direction, passes through the dura, which gives it a cover in S2 and extends to the first coccygeal vertebra. This structure
It is called the filum terminale, and indicates the regression path of the spinal cord, while supporting this structure (the portion covered by the dura and extending from S2 to the coccyx, is also called the coccygeal ligament). The dorsal and ventral roots of the spinal nerves below the terminal end of the medulla at L2-L3 together constitute the
cauda equina (horsetail). When a cerebrospinal fluid extraction is done using a lumbar puncture, the needle is inserted into the lower lumbar region (L4-L5) to avoid the lower end of the spinal cord.
31 июл 2024
