Figure 1.

Olfactory circuit and pathological changes associated with Alzheimer’s disease (AD). The olfactory circuit begins with olfactory sensory neurons (OSNs) of the olfactory neuroepithelium (ONE), whose axonal extensions form olfactory nerve fibers that cross the cribriform plate of the ethmoid bone to penetrate the olfactory bulb, where they establish synapsis with mitral cells. Mitral cells send their axonal projections in a bundle that forms the olfactory tract, which connects the olfactory bulb with the upper olfactory areas. The olfactory tract is divided into the medial olfactory striae, whose axons go to the fornix, and the lateral olfactory striae, which connect with the olfactory cortex (piriform cortex, entorhinal cortex, and the amygdala). In each of these structures, pathological changes associated with AD have been evident, and they may even be present in mild cognitive disorder (MCI), as represented in the figure [161,162,163,164,165,166,167].