It is generally accepted that the border between the spinal cord and the brain passes at the level of the intersection of the pyramidal fibers (although this border is very arbitrary) or at the level of the occipital foramen of the occipital bone. Inside the spinal cord there is a cavity called the central canal (Latin canalis centralis) which is filled with cerebrospinal fluid.
The spinal cord is protected by the pia, arachnoid and dura mater. The spaces between the membranes and the spinal canal are filled with cerebrospinal fluid. The dura mater consists of the visceral and parietal sections. The space between the visceral and parietal dura maters is called the epidural space and is filled with adipose tissue and venous network.
The spinal cord (Latin medulla spinalis) has a clear segmental organization. It provides connections between the brain and the periphery and performs segmental reflex activity. The spinal cord lies in the spinal canal from the upper edge of the 1st cervical vertebra to the 1st or upper edge of the 2nd lumbar vertebra, repeating the direction of curvature of the corresponding parts of the spinal column. In a fetus at the age of 3 months, it ends at the level of the V lumbar vertebra, in a newborn, at the level of the III lumbar vertebra.
The spinal cord without a sharp border passes into the medulla oblongata at the exit of the first cervical spinal nerve. Skeletotopically, this border runs at the level between the lower edge of the foramen magnum and the upper edge of the first cervical vertebra.
At the bottom, the spinal cord passes into a conical point (lat. conus medullaris), continuing into the terminal (spinal) thread (lat. filum terminale (spinale)), which has a diameter of up to 1 mm and is a reduced part of the lower spinal cord. The terminal thread (with the exception of its upper sections, where there are elements of the nervous tissue) is a connective tissue formation.
Together with the dura mater, it penetrates the sacral canal and attaches at its end. That part of the terminal thread, which is located in the cavity of the dura mater and is not fused with it, is called the internal terminal thread (lat. filum terminale internum), the rest of it, fused with the dura mater, is the outer terminal thread (lat. filum terminale externum). The terminal thread is accompanied by the anterior spinal arteries and veins, as well as one or two roots of the coccygeal nerves.
The spinal cord does not occupy the entire cavity of the spinal canal: between the walls of the canal and the brain there is a space filled with adipose tissue, blood vessels, meninges and cerebrospinal fluid
