Embryogenesis of the spinal cord
The development of the spinal cord (medulla spinalis) originates from the trunk region of the neural tube. During embryogenesis, the wall of this tube thickens and differentiates, forming three distinct layers (viewed from the inside, from the canal lumen outwards):
- Inner layer (ependyma). The deepest layer adjacent to the central canal. During development, it gives rise to ependymal glia, which forms the lining of the spinal canal.
- Middle layer (mantle layer). The intermediate zone of the neural tube. This layer is the source of the spinal cord gray matter, which histologically represents an accumulation of neuronal cell bodies.
- Outer layer (marginal velum). The peripheral part of the wall. During differentiation, this layer transforms into white matter, formed by myelinated nerve fibers.
Histological structure of the meninges
The spinal cord, similarly to the brain, is covered by three meninges. They differ in the type of connective tissue and anatomical features of their arrangement.
- Pia mater. Formed by loose fibrous connective tissue. Its main feature is its tight adherence to the spinal cord tissue. The membrane precisely follows the entire complex relief of the organ, extending into all depressions and sulci. It is here that a large number of blood vessels are located, providing trophic support to the nervous tissue.
- Arachnoid mater. Like the pia mater, it consists of loose fibrous connective tissue. However, unlike the former, it does not extend into the depressions and sulci of the spinal cord, but rather «bridges» across them.
- Dura mater. The outermost and toughest layer. Unlike the two internal meninges, it is formed by dense fibrous connective tissue, which provides reliable mechanical protection for the organ.
Subarachnoid space
The difference in syntopy (apposition) of the pia mater and arachnoid mater forms an important anatomical structure — the subarachnoid space.
Because the pia mater descends to the bottom of the spinal cord sulci while the arachnoid bridges over them, a cavity (space) is formed between these two layers of loose connective tissue. This topographic feature is critically important for understanding fluid circulation within the spinal canal.
Briefly: answers to topical questions
Where is the subarachnoid space of the spinal cord located and what is it filled with?
The subarachnoid space of the spinal cord is located between the arachnoid mater and the pia mater. It is filled with cerebrospinal fluid (CSF).
What structures bound the epidural space of the spinal cord?
The epidural (extradural) space of the spinal cord is located between the periosteum of the vertebral canal and the dura mater. When describing the splitting of the spinal dura mater, it corresponds to the space between the outer layer, which transitions into the periosteum of the vertebral canal, and the inner layer, which envelops the spinal cord.
What type of cells lines the central canal of the spinal cord?
The central spinal canal is lined with ependymal glia, which consists of ependymocytes. The tissue organization is predominantly a single-layer sheet of cylindrical cells.
Distinctive cell features:
- Nuclei — dark, elongated, oriented perpendicularly to the surface.
- Apical surface — contains microvilli and motile cilia (kinocilia) that ensure fluid flow within the canal.
- Basal surface — characterized by the absence of a basement membrane over most of its extent.
Neural tube layers from inside out: «Epi Mantle Marginal» (Ependymal, Mantle, Marginal velum).
Class and exam questions
From which germ layer derivative does the spinal cord develop?
The spinal cord develops from the trunk region of the embryonic neural tube.
What is formed from the mantle layer of the neural tube?
The middle (mantle) layer of the neural tube is the source of development for the gray matter of the spinal cord, where neuronal cell bodies accumulate.
How does the dura mater differ histologically from the pia and arachnoid maters?
The dura mater is formed by dense fibrous connective tissue, whereas the pia and arachnoid maters consist of loose fibrous connective tissue.
How is the subarachnoid space formed?
It is formed as a cavity between the pia and arachnoid maters due to the fact that the pia mater tightly adheres to the sulci of the brain, while the arachnoid does not enter them, bridging across from above.
What else to study on this topic
- Structure of ependymal glia and canal lining
- Cytoarchitecture of the spinal cord gray matter
- Myelinated nerve fibers of the white matter
- Vascularization of the pia mater
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