These receptor cells send signals into the brain through a thin section of the skull located between the eyes, termed the cribriform plate. Signals are conducted from an overlying olfactory bulb to higher brain centers associated with arousal, emotional phenomena, and cognition. The olfactory system is vitally important in determining food flavors. During chewing and swallowing, odor-laden air is forced from the rear of the oral cavity to the olfactory receptors, evoking many flavor sensations that people usually associate with taste but that are almost completely dependent on the sense of smell. If the nose is held while food is being swallowed, the free flow of air to the olfactory receptors is prevented, resulting in a decrease or elimination of the perception of the food's taste.
Numerous factors influence the ability to smell.
For instance, women, on average, have a better sense of smell than men. Older persons typically develop anosmia, or loss of smell function. Various diseases, head injuries, and exposure to airborne toxins, including cigarette smoke, may cause a lessened smell function or a distortion of smell function, such as perceiving a bad smell while smelling flowers. Recent studies suggest that alterations in the ability to smell may be an early first sign of such disorders as Alzheimer's disease and parkinsonism. Fewer factors influence taste perception.