In Figure 9, the olfactory system consists of five main components: the olfactory hairs or nerve fibres (item 1), the olfactory cells (item 2), the previously mentioned olfactory bulbs (item 3) and special nerve cells (item 4) found in the olfactory tracts (item 5). The nasal cavity is a space in the nose that lies just above the roof of the mouth. The olfactory hairs are normally found at the top of the nasal cavity, ready to detect a smell coming through the nostril. The detected smell is converted into a tiny electrical signal by the olfactory cells anchored to the olfactory bulb and sent through the nerve cells or neurons along the olfactory tract to those regions of the brain where it can be identified and recognised as a particular smell. There is one olfactory bulb and tract for each nostril.

This was first documented by Aureliano Maestre de San Juan in 1856 (see answer to Question 2). In Kallmann's syndrome, it is mainly the olfactory bulbs and tracts which are either partially formed or missing altogether. However, some olfactory cells may well be present at the top of the nasal cavity, but they are useless since there is no communication link between them and the brain. Consequently, somebody with Kallmann's syndrome finds it impossible to identify a particular smell.