Human diseases and the olfactory system

Olfactory receptor neurons are located in the nasal epithelium. The axons of these neurons project directly to the olfactory bulb, a part of the cerebral hemisphere. This anatomical arrangement provides a direct link between the central nervous system and the organism s external environment including the possible entry of pathogens and neurotoxic chemicals into the brain (McLean et al. 1989). 

Until recently, olfaction has received limited attention in pathological conditions in man. Recent interest in the human olfactory system has been brought about, in part, by neuropathological investigations that described the presence of histological lesions in olfactory-related structures in Alzheimer s disease (Reyes et al. 1987 Pearson et al. 1985 Esiri and Wilcock, 1984), a condition clinically characterized by progressive intellectual decline and behavioral abnormalities. Other clinical studies have shown that olfactory deficits occur in patients with Alzheimer s disease (Doty and Reyes, 1987 Doty et al. 1988), Parkinson s disease (Doty et al. 1988) and schizophrenia. 

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