This article provides a reasoned explanation to two questions about the anatomy of the human central nervous system: why does the spinal cord not occupy entirely the interior of the lumbar vertebral canal? And what is the reason that the adult spinal cone (CM) (the caudal end of the spinal cord) is above L3? To answer the first question, we will use the phylogeny and ontogenicity of the human species. In vertebrates, the greater the amplitude of movements of anti-posterior flexion and rotation of the spine, the greater the difference between the length of the spinal cord and the spine, which explains that in humans, The spinal cord does not completely occupy the interior of the lumbar canal. Through biomechanics studies, we can solve the second question. During walking, at each step, the scapular belt and the part of the spine above L3 rotate in unison in the same direction. The pelvic girdle and the part of the column below L3 are rotated in the opposite direction (counter-rotation). If the MC (Spinal Cone) was below L3, rotation and counter-rotation movements would cause torsion and spinal ischemia. As in man the CM is located above L3, the spinal cord in its entire extent rotates in the same direction as the shoulder girdle, thus avoiding the appearance of spinal torsions. What is the clinical interest of human medullary biomechanics? His study can contribute to the understanding of the pathophysiology of spinal cord diseases such as "tethered cord syndrome" and ischemic syringomyelitis, and help to design less iatrogenic medical treatments for neural tube neurologic diseases.
INTRODUCTION
In the anatomy of living beings, form has a meaning, a purpose. Maintaining unnecessary structures would involve additional energy expenditure that could compromise the survival of a species. So, if the structure of the anatomical components serves a physiological function, why does the human spinal cord not completely occupy the interior of the spinal canal ? and why is the caudal end of the spinal cord, or conus medullaris (CM), located between vertebrae T12 and L3 ? (1)
According to Haeckel’s biogenetic law, ontogeny recapitulates phylogeny (2). The morphological changes that occur during embr...
