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Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss olfaction.
Olfaction refers to the sense of smell, which begins with a specialized collection of cells
called the olfactory epithelium.
In humans, the olfactory epithelium lines the nasal cavities.
The olfactory epithelium contains millions of olfactory receptor cells.
These cells have a single dendrite that extends to the outermost layer of the epithelium,
where cilia emerge from the end of the dendrite and spread over the surface of the olfactory
epithelium.
When odorants enter the nasal cavity due to inhalation or by rising from the mouth during
the chewing of food, they stimulate receptors on the cilia, depolarizing the olfactory receptor
cells and initiating action potentials that travel down the axon of the receptor cell
into an adjacent structure called the olfactory bulb.
These axons that travel from the olfactory epithelium to the olfactory bulb together
make up the first cranial nerve.
In the olfactory bulb the axons of the olfactory receptor cells converge on the dendrites of
olfactory bulb neurons in small clusters called glomeruli.
In these glomeruli, the receptor cells form synaptic connections with several types of
olfactory bulb neurons, including cells called mitral cells and tufted relay neurons.
Both of these cells project into the olfactory tract, a bundle of fibers that carries olfactory
information to the olfactory cortex, where most olfactory processing occurs.
The olfactory cortex consists of a collection of cortical areas that receive information
from the olfactory bulb, including the piriform cortex, an area of cortex surrounding the
amygdala known as the periamygdaloid cortex, entorhinal cortex, and two regions known as
the olfactory tubercle and anterior olfactory nucleus.