Every now and then I am asked if the spinal cord has the possibility of movement or if it is linked to the various vertebral levels. Well, from studies carried out on both cadavers and living people, such as the one carried out by A. Brieg, it emerged that the spinal cord and its nerve roots are capable of some degrees of plastic bending. Specifically, in conditions of normal flexion and extension of the column, the contents of the medullary canal follow the changes in length and curvature of the canal itself without being moved in the slightest within the canal itself. These variations in length are of the order of 4.5-7.5 cm (calculating from the midbrain to the medullary cone on the dorsal part of the medullary canal). Of these centimeters, 0.8-1.4 cm is the possible lengthening of the brainstem, 1.8-2.8cm the cervical cord, 1-2cm the thoracic cord.
When the spine is in maximum lordosis (dorsal extension), the microscopic examination highlighted a wavy folding of the cylinders of the axis within the spinal cord and a shortening of the nerve roots.
However, when the spine is in maximum kyphosis (ventral flexion), the lengthening of the spinal cord occurs mainly with the unwinding and straightening of the cylinders of the axis and the other elements of the spine.
Furthermore, in ventral flexion, the pia mater appears to undergo axial traction, while in dorsal extension a horizontal traction occurs (corresponding to the compressed shortening canal with its widened cross-section). The pia mater has been seen to follow these forces without appreciable resistance, and its components take the direction of the force.
At maximum lengthening of the canal the pia showed 'sudden stiffening' and the ability to sustain a traction of 2-3kg before breaking.
In the upright position at rest there is no tension in any element of the components of the spinal canal.
In the same study Brieg made similar observations on the posterior brain, that is, on the contents of the posterior fossa of the skull from the midbrain to the lower end of the medulla oblongata. During the movement of the head and neck (flexion, extension, and lateral flexion at the level of the atlanto-occipital and atlanto-axial joints) deformations were highlighted at the level of the brainstem, parts of the cerebellum and cranial nerves from V to XII, with maximum shape alterations in the dorsal part of the medulla oblongata.
In ventral flexion the cranial nerves stretch between the brainstem and the exit foramen at the base of the skull.
In dorsal extension, axial compression of these structures gives rise to shortening and widening of the brainstem and undulating bending of the cranial nerves.
It is also possible to transmit traction on the canal to the brainstem and related cranial nerves.
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