Lab 6 - Auditory, Vestibular, Gustatory and Olfaction Systems

Central Olfactory Pathway

The olfactory bulb and olfactory tract are found on the inferior surface of the whole brain. The bulb and tract normally are located in the olfactory sulcus, which separates the orbital gyrus from the gyrus rectus of the frontal lobe. The olfactory tract contains the lateral and medial olfactory tracts. Follow it caudally until it divides at the olfactory trigone into the lateral and medial olfactory tracts. If the temporal lobe is lifted part of the piriform cortex can be seen. Find the uncus which appears as a small knob on the medial side of the rostral pole of the parahippocampal gyrus. The uncus lines the medial surface of the amygdaloid nucleus. The periamygdaloid cortex covers the rostral and superior regions of the uncus and is continuous with the piriform cortex. More caudally and inferiorly, the entorhinal cortex constitutes a major portion of the rostral parahippocampal gyrus. Together the piriform cortex, periamygdaloid cortex and entorhinal cortex are sometimes referred to as the piriform lobe.

Figures 1 and 2 show microscopic coronal sections through the telencepahlon. Figure 2 is more anterior than fig. 1 (note the globus pallidus beginning to make an entrance on the right side of fig. 1). Note that the olfactory tract has already separated into the lateral and medial olfactory tracts. In these two figures we can only see the lateral olfactorytract.

In Figure 3, find the lateral olfactory tract, which can be seen coursing laterally. It projects to the primary olfactory cortex, which is composed of the cortex overlying the lateral olfactory tract and the area of the medial tip of the uncus and to the amygdala. The anterior part of the parahippocampal gyrus (part of the entorhinal cortex) is an olfactory association area.