Pyramid-shaped mitral cells are the largest neurons in the bulb and are located in a narrow band between the external and internal plexiform layers. The granule cell layer contains multiple, small, round neurons that lack axons. Long dendritic processes of the neurons reach the more superficial layers and inhibit mitral cells and tufted cells. Small distal processes make contacts with the exiting mitral cell axons. Medial fibers of the tract contact the anterior olfactory nucleus and the septal area.
Some fibers project to the contralateral olfactory bulb by way of the anterior commissure.
Third-order neurons send projections to the dorsomedial nucleus of the thalamus, the basal forebrain, and the limbic system. The thalamic connections are thought to serve as a conscious mechanism for odor perception, while the amygdala and the entorhinal area are limbic system components and may be involved in the affective components of olfaction. Regional cerebral blood flow investigations have demonstrated a significant increase in the amygdaloid nucleus with the introduction of a highly aversive odorant stimulus, and this has been associated with subjective perceived aversiveness. The pyriform lobe includes the olfactory tract, the uncus, and the anterior part of the parahippocampal gyrus. The entorhinal area is known as the secondary olfactory cortex and also is included in the pyriform lobe.