Quick Answer: Olfaction, or the sense of smell, is the special sense through which smells are perceived. It occurs when an odor binds to a receptor within the nasal cavity, transmitting a signal through the olfactory system. Olfaction has many functions, including detecting hazards, and pheromones, and plays a role in taste. Glomeruli aggregate signals from these receptors and transmit them to the olfactory bulb, where the sensory input will start to interact with parts of the brain responsible for smell identification, memory, and emotion. There are many different causes for alteration, lack, or disturbance to normal olfaction, and can include damage to the peripheral nose or smell receptors, or central problems affecting the brain. Some causes include upper respiratory infections, traumatic brain injury, and neurodegenerative disease.