These are molecules in the air that enter the nasal cavity and bind to specific receptors. 

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Olfactory transmission to the brain involves many parts that are necessary to understanding how smell is perceived. 

- odorants
- olfactory bulb
- glomerulus
- mitral cells
- prepyriform cortex 
- orbitofrontal cortex
- amygdala 

It should be noted that olfaction is the only sensory process that does not pass through the thalamus before synapsing in the cortex. 



Olfactory transmission to brain regions

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Odorants

The olfactory bulb is a part of the brain that receives axons from the olfactory receptor neuron. In comparison to other animals, humans have a smaller olfactory bulb in proportion to the brain. 

Olfactory bulb

This is a part of the olfactory bulb and consists of spherical neural circuits. Here, olfactory receptor neuron axons form a synapse on cells in the olfactory bulb called mitral cells. 

Glomerulus

These are cells in the olfactory bulb which receive input from olfactory receptor neurons in the glomeruli. These cells conduct this smell information to various regions in the brain. 

Mitral cells

 This is the primary olfactory cortex in humans. It is highly activated during a sniff when an odor is present, according to fMRI studies (Sobel et al., 2000). 

Prepyriform cortex 

Some projections from the mitral cells of the olfactory bulb reach the amygdala, which is one of the main brain regions responsible for emotion. The link between olfaction and the amygdala suggests answers for why smell is so strongly associated with emotions. 

Amygdala in olfaction

Orbitofrontal cortex in olfaction

The primary olfactory cortex is a brain region located in close proximity to the gustatory cortex. It receives olfactory information directly from the olfactory bulb to process the sense of smell.

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