The membranes of the spinal cord

The spinal cord is surrounded by three membranes of mesenchymal origin. The outer one is the dura mater of the spinal cord. Behind it lies the middle one - the arachnoid mater, which is separated from the previous one by the subdural space. The inner soft mater of the spinal cord is directly adjacent to the spinal cord. The inner membrane is separated from the arachnoid by the subarachnoid space. In neurology, these last two, as opposed to the dura mater, are usually called the soft mater.

The dura mater of the spinal cord (dura mater spinalis) is an elongated sac with fairly strong and thick (compared to other membranes) walls, located in the spinal canal and containing the spinal cord with the anterior and posterior roots of the spinal nerves and the remaining membranes. The outer surface of the dura mater is separated from the periosteum lining the inside of the spinal canal by the suprathenic epidural space (cavitas epiduralis). The latter is filled with fatty tissue and contains the internal vertebral venous plexus. Above, in the region of the foramen magnum, the dura mater of the spinal cord firmly fuses with the edges of the foramen magnum and continues into the dura mater of the brain. In the spinal canal, the dura mater is strengthened by processes continuing into the perineural membranes of the spinal nerves, which fuse with the periosteum in each intervertebral foramen. In addition, the dura mater of the spinal cord is strengthened by numerous fibrous bundles directed from the membrane to the posterior longitudinal ligament of the spinal column.

The inner surface of the dura mater of the spinal cord is separated from the arachnoid by a narrow slit-like subdural space, which is penetrated by a large number of thin bundles of connective tissue fibers. In the upper parts of the spinal canal, the subdural space of the spinal cord freely communicates with a similar space in the cranial cavity. Below, its space ends blindly at the level of the 11th sacral vertebra. Below, the bundles of fibers belonging to the dura mater of the spinal cord continue into the terminal (external) thread.

Arachnoid mater of the spinal cord(arachnoidea mater spinalis) is a thin plate located medially from the dura mater. The arachnoid membrane fuses with the latter near the intervertebral openings.

Pia mater (vascular) of the spinal cord(pia mater spinalis) is tightly adjacent to the spinal cord, fused with it. Connective tissue fibers branching off from this membrane accompany the blood vessels and penetrate with them into the substance of the spinal cord. The arachnoid space (cavitas subarachnoidalis) separates from the soft membrane and is filled with cerebrospinal fluid (liquor cerebrospinalis), the total amount of which is about 120-140 ml. In the lower sections, the subarachnoid space contains the roots of the spinal nerves surrounded by cerebrospinal fluid. In this place (below the second lumbar vertebra), it is most convenient to obtain cerebrospinal fluid for examination by puncturing with a needle (without the risk of damaging the spinal cord).

In the upper sections, the subarachnoid space of the spinal cord continues into the subarachnoid space of the brain. The subarachnoid space contains numerous connective tissue bundles and plates that connect the arachnoid mater with the pia mater and the spinal cord. From the lateral surfaces of the spinal cord (from the pia mater covering it), between the anterior and posterior roots, to the right and left, a thin strong plate extends to the arachnoid mater - the dentate ligament (ligamentum denticulatum). The ligament has a continuous origin from the pia mater, and in the lateral direction it is divided into teeth (20-30 in number), which fuse not only with the arachnoid, but also with the dura mater of the spinal cord. The upper tooth of the ligament is at the level of the foramen magnum, the lower - between the roots of the 12th thoracic and 1st lumbar spinal nerves. Thus, the spinal cord appears to be suspended in the subarachnoid space by means of the frontally located dentate ligament. On the posterior surface of the spinal cord along the posterior median groove from the pia mater to the arachnoid, there is a sagittally located septum. In addition to the dentate ligament and the posterior septum, in the subarachnoid space there are inconstant thin bundles of connective tissue fibers (septa, threads) connecting the pia mater and arachnoid mater of the spinal cord.

In the lumbar and sacral sections of the spinal canal, where the bundle of spinal nerve roots (cauda equina) is located, the dentate ligament and posterior subarachnoid septum are absent. The fat cell and venous plexuses of the epidural space, the membranes of the spinal cord, the cerebrospinal fluid and the ligamentous apparatus do not constrain the spinal cord during spine movements. They also protect the spinal cord from jolts and concussions that occur during human body movements.

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