Smell and taste are considered types of chemosensation, which is the neurological sensing of a chemical stimulus.
Olfactory sense neurons of are located in strategic areas within the nasal cavities. These olfactory sense neurons connect directly to the brain through the olfactory bulb. When exposed to a stimulus, the olfactory nerve endings react, delivering an electrical impulse to the brain, which then identifies the smell. This pathway is extremely sensitive, and may become altered with head trauma or respiratory infections. Common smell disorders include hyposmia and anosmia. Hyposmia is the reduced ability to detect odors while anosmia is complete inability to detect odors. Common causes of smell disorders include nasal obstruction, such as polyps, changes in mucus character, or structural deformity. Medications, hormonal imbalances and age also affect the sense of smell.
Taste buds of the tongue called house gustatory cells, which react to the presence of food particles. Taste sensations are believe to be either sweet, sour, salty, bitter or umami (savory). Humans are born with over 10,000 taste buds. Disorders of taste can be caused by poor oral hygiene and dental problems, alterations in saliva character, head injury, medications (most notably chemotherapy) and certain surgeries to the nose, ear or throat.
In order to diagnose disorders of smell or taste, a “scratch and sniff” test is available for smell. In order to determine the sense of taste, a patient can be given table salt, white sugar, quinine hydrochloride and citric acid. Umami (a recent addition to the taste spectrum) is found in foods such as chicken broth, which could be included in the test. With a process of tongue mapping, identification of the location of loss of taste can point to area of damage. One must be aware that flavor is a combination of both the taste and smell systems.