Chemoreceptors: Detecting Odors, Tastes, and Irritants

Chemoreceptors are sensory neurons that transduce chemical stimuli into neural signals. They mediate smell (olfaction), taste (gustation), and chemesthesis (irritant detection).

Locations and Stimuli

System	Receptor Location	Primary Stimuli	Cranial Nerve
Olfaction	Olfactory epithelium (roof of nasal cavity)	Volatile odorants	CN I (Olfactory)
Gustation	Taste buds (tongue, palate, epiglottis, throat)	Sweet, sour, salty, bitter, umami	CN VII, IX, X
Chemesthesis	Free nerve endings (mucous membranes: eyes, nose, mouth, airway, gut)	Irritants (capsaicin, menthol, ammonia, CO2, smoke)	CN V, IX, X

Physiological Roles

• Olfaction: Hazard detection (smoke, spoiled food), flavor perception (retronasal), social/sexual signaling.
• Gustation: Nutrient/toxin evaluation; initiates digestive secretions (cephalic phase).
• Chemesthesis: Protective reflexes (cough, sneeze, gag, lacrimation, bronchoconstriction).

Clinical Notes

• Anosmia/ageusia: COVID-19, neurodegenerative diseases, trauma, sinusitis.
• Chemesthesis loss impairs airway protection.
• Chemoreceptor dysfunction affects nutrition, safety, quality of life.