Posted: Oct 08, 2019 10:29 am
by zoon
ZoonoTIKK wrote:There are these papers which strongly imply that the inner ear hair cells, and not the medulla, is primarily the driving factor in the CO2 drive reflex

https://www.ncbi.nlm.nih.gov/pubmed/21130842

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3988803/

But every fMRI study done on chemoreceptors has shown only areas of the brain and carotid bodies light up in response to CO2. I could not find any fMRI study papers showing that the inner ears light up in response to CO2 or any histological evidence that the hair cells of the inner ear are chemosensitive and play a larger role in chemosensation than the brain like these studies are trying to imply. It is said the central chemoreceptors in the brain contribute to 85% of the CO2 drive reflex and the peripheral chemoreceptors contribute 15%, which seems to leave little room for the inner ear hair cells to play such a vital and significant part (53% of the respiratory drive was lost when both ears were damaged).

The papers in question were trying to link SIDs to inner ear damage.

Welcome to a more complex life-form than myself! I have no specialist knowledge in these matters, so I’m speculating as an amateur.

As you say, the studies which you link to are examining the effect of inner-ear damage. Perhaps the CO2 drive reflex depends on a functioning inner ear, for example, the hair cells may be sending out a baseline stream of nerve impulses which interact with the signals from CO2 chemoreceptors? This would explain the results even if there are no relevant chemoreceptors in the inner ear, and no extra response to CO2. The ears of tetrapods may originally have evolved for breathing, according to a 2006 paper described in an article here, so it might not be entirely surprising if they still have some link to respiratory control?

My suggestion isn’t convincing from an evolutionary point of view, as it’s supposing that a vestigial link with a negative effect on survival has been maintained for many millions of years.