The sense of smell is different from the other senses in that its sensory pathways are

composed mostly of motor neurons
activated only by gaba
longer
not routed directly through the thalamus

The olfactory system is involved in the sense of smell. The receptors of smell are not routed through the thalamus. The signals id directly routed from the olfactory bulb to the olfactory cortex and thalamus is not contacted in between. This is the difference between the taste and smell receptors, although both of their receptors are stimulated from mucus/saliva in the mouth.