Our sense of smell is one of our 2 chemical senses. The other being the sense of taste. Both allow us to be aware of substances in our environment and rely on our ability to detect these substances by the chemical nature of their molecules. Our other senses allow us to be aware of the physical characteristics of our environment - its temperature, the presence of radiation (e.g. visible) and the texture of materials with which we are in contact.
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Odour molecules entering the nose are thought to be recognized by receptors found in cilia of olfactory neurons. Neurons with specific receptors are arranged randomly within zones in the olfactory lining of the nasal cavity. Signals from neurons with the same receptors converge on structures called glomeruli in the olfactory bulb. The pattern of activity in these glomeruli creates a pattern or code that the brain may interpret as different odors. The information is carried by nerve fibers to many brain regions, where it affects thoughts, emotions, and behavior. picture from: http://www.sfn.org/content/Publications/BrainBriefings/smell.html |
The sense of smell is stimulated only by gaseous molecules. These may come directly from the air we breathe or may come from volatile substances, released in our mouth, from the food we are eating. The molecules we perceive as smells are called odorants. Odorant molecules stimulate sensory nerve cells at the top of the nasal cavity and these respond by sending impulses to the brain. The sensory nerve cells involved are called receptor cells, their surfaces have regions on them called receptor sites. These detect the odorant molecules and the process triggers a sequence of changes in the cell that eventually generate an electrical signal.
Olfactory information travels not only to the limbic system, which refers to the primitive brain structures that govern emotions, behavior, and memory storage, but also to the brain's cortex, or outer layer, where conscious thought occurs. In addition, it combines with taste information in the brain to create the sensation of flavor. Thus odours have a profound effect on our thoughts, emotions and behavior.
