Olfactory system

The olfactory system is also known as our sense of smell. It is the sensory system used for olfaction. It is the most sensitive of our senses and helps us to identify many different (millions of) aromas around us, in the atmosphere. 

Most mammals and reptiles have two parts to their olfactory system. 
There is a main olfactory system, which detects volatile, airborne substances. 
There is secondary, or accessory, system. The accessory olfactory system senses fluid-based stimuli. Behavioral evidence indicates that most often, the stimuli detected by the accessory olfactory system are pheromones.

The olfactory system is often spoken as being similar to the gustatory system (taste system). Both are chemosensory senses. They change chemical signals into nerve impulses, which are translated into perceptions in the brain.

The part of the brain which deals with olfaction is the rhinencephalon, a small part in the human brain, but much more important in other vertebrates. The piriform cortex is probably the area most closely associated with identifying the odor. The medial amygdala is involved in social functions such as mating and recognising animals of the same species. The entorhinal cortex pairs odors with memories.  

These systems give us advanced warnings about the environment and also plays a very important role in how we recognise and successively communicate with each other. Smell is closely linked to memory and experience and the subtle connection between a smell and an object or person adds to the memory. The exact functions of these higher areas is still being researched. 

Linda B. Buck and Richard Axel won the 2004 Nobel Prize in Physiology or Medicine for their work on the olfactory system. Buck L. & Axel R. 1991. A novel multigene family may encode odorant receptors: a molecular basis for odor recognition. Cell 65 (1): 175–187.   By analyzing rat DNA, they estimated that there were about one thousand different genes for olfactory receptors in the mammalian genome. 

 Damage 
Damage to the olfactory system can happen through brain injury, cancer or toxic gases. The damage is usually measured by doctors giving the patient something to smell and having the patient try to guess what it is.

 Related pages 
Olfaction
Gustatory system
Memory 
Learning and fear based learning, learned helplessness 

 References 

Category:Sensory system