Some of my students asked me that question and i can't give them a good answer. Of course, when you are a new born child, your spinal cord touch s1 and because of bones growing, it comes progressivly to L2. But Why ? Phylogenetic ? protection ? efficiancy ? By the way, the terminal cone see a lot of myelomer in a very narrow space. it does not seems to be very convenient ...
Hi Eric,
"Why" is a kind of a question we often cannot answer. We all have, as a result how biology has been taught to us, a tendency to adopt a functionnal answer. But, here, it doesn't seem obvious. Growth allometry? why not... The location of the ending of the spinal chord is highly variable within vertebrates and, for instance, a short spinal cord extending very few in the spinal canal is a well known feature, being a synampomorphy of both Tetraodontiformes (ocean sunfih, boxfish, triggerfish and puffers...) and Lophiiformes (anglers, monkfishes). In order to avoid functionnal answers, have a look on the diversity of this feature among mammals. Does the same thing occur in some related species ?
good luck hope it helps
Bruno
Eric,
your question stayed in my mind and I found that more than the ending of spinal cord, there is a variability within mammal species regarding the different tracts present in the spinal cord ... and that thevanswer to your question is, as often, a mixture of functionnality and phylogeny. For instance, the corticospinal tract extends to coccygeal level in Primates. But in rabbit, ungulates and others extends to cervical level....
more in :
Comparative Vertebrate Neuroanatomy: Evolution and Adaptation, by Ann B. Butler,William Hodos (2005)
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