ORN respond to the continued presence of an odorant by reducing their frequency of firing. Such adaptation probably arises from an increase in intracellular calcium generated by the initial depolarization. Table 14.1 shows the second messenger system used by some of the common odorants. The olf nerve carries the info to the olf bulb, which lies on the ventral, anterior side of the ipsilateral forebrain. The most distinctive feature of the bulb is an array of spherical structures called glomeruli , shown in Fig.
Mitral cells are the principal projection neurons of the bulb.
It is believed that these local circuit neurons sharpen the chemical selectivity of the mitral cells. The axons of the pyramidal cells in the pyriform cortex project in turn to several brain regions as shown in Fig.