Distribution of Olfactory and Nonolfactory Surface Area in the Nasal Fossa of Microcebus murinus: Implications for Microcomputed Tomography and Airflow Studies

Abstract

The nasal fossa of most mammals exemplifies extreme skeletal complexity. Thin scrolls of bone (turbinals) that both elaborate surface area (SA) and subdivide nasal space are used as morphological proxies for olfactory and respiratory physiology. The present study offers additional details on the nasal fossa of the adult mouse lemur (Microcebus murinus), previously described by Smith and Rossie (Smith and Rossie [2008]; Anatomical Record 291:895-915). Additional, intervening histological sections of the specimen were used to map and quantify the distribution of olfactory and nonolfactory mucosa on the smaller turbinal of the frontal recess (FR; frontoturbinal) and those that occur between ethmoturbinals (ETs; interturbinals). A second adult Microcebus specimen, available as a dried skull, was scanned using microcomputed tomography (microCT) and reconstructed to infer the position of these turbinals within the nasal airway. Overall, turbinal bones comprise more than half of internal nasal SA. All ETs combined comprise about 30% of total nasal fossa SA, and contribute nearly half of all olfactory SA. Of these, the nasoturbinal (NT) is most completely covered with olfactory mucosa, whereas ET I is least covered with olfactory mucosa. The FR contributes significantly to total olfactory SA (ca. 20%). This recess and the single frontoturbinal within it lie in a more lateral pathway of airflow compared with interturbinals, which lie in more central zone just anterior to the olfactory recess of Microcebus. Variations in the turbinals and recesses that complicate central and paranasal in primates should be investigated further in light of zone-specific distributions of olfactory receptors (ORs) that differ between these regions in rodents. Anat Rec, 294:1217Rec, 294: -1225

The role of the olfactory recess in olfactory airflow

“…Our study shows that variations in the size of the olfactory recess likely have significant functional consequences in groups that exhibit extensive variation in olfactory recess size, such as bats and primates (Cave, 1973;Moore, 1981;Smith et al, 2011;Smith et al, 2012;Smith et al, in press). This work also adds to the growing body of computational modeling studies that investigate the role of morphology in airway function.…”

Tour of a Labyrinth: Exploring the Vertebrate Nose

“…Thus, the short snout of feliforms appears to have reduced the space available for the maxilloturbinal, allowing the anterior ethmoturbinals to lie in the respiratory air pathway (Fig. ), a pattern also observed in some primates (Smith et al, ).…”

“…These turbinals are the primary location for olfactory epithelium, but may also participate in respiratory air‐conditioning in some primates (Smith et al, ; DeLeon and Smith, ) and short‐snouted carnivorans (Van Valkenburgh et al, ). In addition, olfactory epithelium can be found rostrally on the nasal septum as well as lining various recesses and the lateral walls of the nasal cavity (Adams, ; Bhatnagar and Kallen, ; Smith et al, ). In many or most mammals, the nasoturbinal has a tube‐like morphology and appears to function in directing air to the posteriorly positioned olfactory region.…”

Role of ortho‐retronasal olfaction in mammalian cortical evolution

“…The architecture of the turbinals and floor of the nasal capsule determines whether orthonasal and/or retronasal air currents pass directly over olfactory epithelium. Turbinals are highly variable between mammalian clades, and only recently has 3D imaging made morphological analysis possible (Van Valkenburgh et al, 2004; Rowe et al, 2005; Smith et al, 2011; Eiting et al, 2015), and shown that they preserve phylogenetic (Macrini, 2012) and ecological (Van Valkenburgh et al, 2011) signals.…”

“…They lie directly in the stream of ortho-retronasal airflow and function in metabolic heat and water balance (Smith et al, 2011; Eiting et al, 2015). Saturation of air within the nose may also play a role in volatilization, but experimental airflow studies are still in their infancy.…”