MicroCT scan of the nasal airway of a domestic short hair cat

The peripheral structures of mammalian sensory organs often serve to
support their functionality, such as alignment of hair cells to the
mechanical properties of the inner ear. Here, we examined the
structure-function relationship for mammalian olfaction by creating an
anatomically accurate computational nasal model for the domestic cat
(Felis catus) based on high resolution microCT and sequential histological
sections. Our results showed a distinct separation of respiratory and
olfactory flow regimes, featuring a high-speed dorsal medial stream that
increases odor delivery speed and efficiency to the ethmoid olfactory
region without compromising the filtration and conditioning purpose of the
nose. These results corroborated previous findings in other mammalian
species, which implicates a common theme to deal with the physical size
limitation of the head that confines the nasal airway from increasing in
length infinitely as a straight tube. We thus hypothesized that these
ethmoid olfactory channels function as parallel coiled chromatograph
channels, and further showed that the theoretical plate number, a
widely-used indicator of gas chromatograph efficiency, is more than 100
times higher in the cat nose than an “amphibian-like” straight channel
fitting the similar skull space, at restful breathing state. The parallel
feature also reduces airflow speed within each coil, which is critical to
achieving the high plate number, while feeding collectively from the
high-speed dorsal medial stream so that total odor sampling speed is not
sacrificed. The occurrence of ethmoid turbinates is an important step in
the evolution of mammalian species that correlates to their expansive
olfactory function and brain development. Our findings reveal novel
mechanisms on how such structure may facilitate better olfactory
performance, furthering our understanding of the successful adaptation of
mammalian species, including F. catus, a popular pet, to diverse
environments.