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The Olfactory Pathways

The document summarizes the olfactory system and pathways. It describes how odorant molecules enter the nasal cavity and are detected by olfactory receptors located in the olfactory mucosa. The receptors send signals along axons to structures called glomeruli in the olfactory bulbs. Information then travels to various parts of the brain involved in smell perception, including the primary olfactory cortex, thalamus, orbitofrontal cortex, amygdala, hypothalamus and limbic system. The complex pathways help explain why smells can elicit strong emotions by activating the limbic system.

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Leo Tolentino
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276 views3 pages

The Olfactory Pathways

The document summarizes the olfactory system and pathways. It describes how odorant molecules enter the nasal cavity and are detected by olfactory receptors located in the olfactory mucosa. The receptors send signals along axons to structures called glomeruli in the olfactory bulbs. Information then travels to various parts of the brain involved in smell perception, including the primary olfactory cortex, thalamus, orbitofrontal cortex, amygdala, hypothalamus and limbic system. The complex pathways help explain why smells can elicit strong emotions by activating the limbic system.

Uploaded by

Leo Tolentino
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Karolina Gajewska Univ.

of Calgary
http://ucalgary.ca/pip369/mod8/smell the olfactory system

The Olfactory Pathways


The Olfactory Stimuli
As shown in the following image, scents (i.e., odorant molecules) can enter your system through a primary and secondary pathway. The primary pathway is through the nose, and the secondary pathway is through the mouth via the pharynx (i.e., the space between the nasal cavity and the mouth). After making their way into the nasal cavity, odorant molecules travel to the olfactory mucosa (also known as theolfactory epithelium), an area about the size of a dime located in the nasal cavity.

The Olfactory Receptors


The olfactory mucosa contains the olfactory receptor neurons that are responsible for scent transduction. The transduction occurs in theolfactory receptors located on cilia at the ends of the olfactory receptor neurons.

Odorant molecules can reach the olfactory receptors via a passive pathway or an assisted pathway. In the passive route, molecules reach the olfactory mucosa via inhaled air. In the assisted pathway, the molecules attach to an olfactory binding protein that transports them directly to the olfactory receptors. Olfactory receptors are protein molecules attached to the olfactory receptor neurons. There are about 1,000 kinds of olfactory receptors; all the olfactory receptors are the same on each olfactory receptor neuron. The attachment of scent molecules to the olfactory receptors creates a series of chemical reactions that result in an action potential in the cilia. The electrical signal is sent via the axons of the olfactory neurons to structures called glomeruli on the left and right olfactory bulbs, which are actually an outcropping of the brain (see the following figure).

The Olfactory Pathways


The organization of the olfactory pathways is highly complex and not yet well understood. It is known that the olfactory receptors located in the same zone of the mucosa send their information to the same glomeruli. As well, the olfactory receptor neurons located in the same zone of the mucosa have similar properties that are not found in other zones. Any particular olfactory receptor neuron will only send a message to a maximum of two glomeruli. Information is conducted from the olfactory bulbs by the lateral olfactory tract to the primary olfactory cortex. From there, it goes to thethalamus (mediodorsal nucleus) and on to the orbito-frontal cortex where conscious smell perception occurs. Primates also have a pathway that runs from the thalamus to the amygdala which is part of the limbic system, and then on to the hypothalamus. The limbic system is involved in the perception of emotions and is responsible for the "affective" component of smell. This may explain why scents can engender strong emotions and/or take us back to previous experiences.

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