Airborne molecules that we can smell enter the nose and come into contact with olfactory receptors on olfactory receptor neurons, which are on a part of the superior nasal cavity called the olfactory epithelium. Axons of olfactory receptor neurons of the olfactory epithelium travel in one of many small nerves that pass through the skull to synapse on intracranial structures called the olfactory bulbs. These multiple small nerves are collectively called the olfactory nerve on that side.
Olfactory bulb neuron axons travel in structures called olfactory tracts to synapse in bilateral primary olfactory cortices, which are on the medial temporal lobes. The olfactory bulbs and tracts are central nervous system tissue, with oligodendrocytes instead of Schwann cells. Olfaction is the only conscious sense that is not relayed through the thalamus prior to reaching the cerebral cortex. Olfactory information is also sent to other cortical and subcortical areas, directly or via the thalamus, for many autonomic, endocrine (hormonal), emotional, and cognitive functions.
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