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

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.

Primary Olfactory Cortex

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. 



Ohio State University, Columbus

Chemicals in the air trigger odor sensation

- receptors in the nose
- transmission to brain regions
- anosmia

Smell

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

Behavioral Neuroscience 8th Edition

In the nose, there are three types of cells in the olfactory epithelium. 

- Olfactory receptor neurons
- Basal cells 
- Supporting cells 

Receptors in the nose 

Olfactory transmission to brain regions

This is a condition in which a person lacks the ability to smell. It is also sometimes referred to as odor blindness. 

Anosmia

This is a highly specialized system that detects pheromones and sends the information to the brain. This system is found in most terrestrial mammals. 

Vomeronasal system

Olfactory training is a non-pharmacological and non-surgical treatment for patients with olfactory dysfunction. UPSIT (University of Pennsylvania Smell Identification Test) is the most common olfactory training in North America. UPSIT is based on microencapsulated odorants released from the surface of strips. Each subject tags 40 odorants on a multiple-choice list.

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