"Nose" - what is it, definition of the term
The nasal organ of rodents such as rats and mice is a protruding structure at the front of the skull that encloses the olfactory epithelium, contains paired nostrils for airflow, and supports sensory vibrissae; it serves to detect airborne chemical cues, regulate breathing, and contribute to thermoregulation.
Detailed information
The nasal region of rodents such as the Norway rat (Rattus norvegicus) and the common house mouse (Mus musculus) comprises a compact skeletal framework, delicate cartilage, and a highly vascularized mucosal surface. The bony portion includes the premaxilla and maxilla, forming a protruding snout that supports the external nares. Surrounding bone, the ethmoid and vomer contribute to the internal nasal cavity, which is partitioned into multiple turbinates that increase surface area for air filtration and humidification.
Olfactory epithelium lines the superior portion of the cavity, containing millions of sensory neurons that detect volatile compounds. In rats, the olfactory epithelium occupies approximately 15 % of the total nasal surface, while in mice it accounts for roughly 12 %. These neurons project axons through the cribriform plate to the olfactory bulb, where odorant signals are processed. The high density of receptors enables discrimination of a wide range of chemical cues, essential for foraging, predator avoidance, and social communication.
Key functional components include:
- Turbinate architecture: Expands mucosal surface; varies in number and curvature between species, influencing airflow dynamics.
- Mucus production: Goblet cells and serous glands maintain a moist layer that traps particles and dissolves odorants.
- Blood supply: Extensive capillary networks regulate temperature and humidity of inhaled air, supporting optimal receptor performance.
- Innervation: Trigeminal nerve fibers innervate the nasal mucosa, providing mechanosensory feedback and contributing to respiratory reflexes.
Developmentally, the nasal structures emerge from the frontonasal prominence during embryogenesis. Gene expression patterns, such as Shh, Fgf8, and Pax6, guide the formation of the nasal placodes and subsequent differentiation of olfactory epithelium. Mutations affecting these pathways result in congenital anomalies that impair scent detection and respiratory function.
Comparative studies reveal that the rat’s snout is proportionally longer than that of the mouse, providing a larger olfactory field and enhanced ability to sample airborne chemicals. This morphological difference correlates with behavioral observations: rats exhibit more extensive exploratory sniffing, whereas mice rely on rapid, localized sampling.
In laboratory settings, the nasal region serves as a model for toxicology and pharmacology. Inhalation exposure experiments assess the impact of particulate matter, volatile organic compounds, and therapeutic aerosols on epithelial integrity, ciliary function, and inflammatory responses. Quantitative measurements, such as epithelial thickness, mucus viscosity, and receptor expression levels, provide standardized endpoints for risk assessment.
Overall, the rodent nasal apparatus integrates complex anatomical, physiological, and genetic elements to support respiration and olfaction. Its accessibility and similarity to human olfactory structures make it a valuable system for investigating sensory biology, disease mechanisms, and environmental health.