anat 321 the olfactory system

8/10/2019 ANAT 321 the Olfactory System

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The Olfactory System

ANAT 321


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The chemical senses are the most ancient and

ubiquitous of the senses.


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Olfaction is more important to some other species

than it is to us.


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http://antranik.org/central-nervous-system-intro-to-brain-and-

ventricles-medulla-oblongata-pons-mid-brain-and-cerebellum/

http://play.psych.mun.ca/~smilway/rat_ventral_text.jpg

Olfactory bulbs of a human and a rat.


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Olfactory transduction takes place within the olfactory epithelium, a 1-2

cm2 patch of cells on the roof and adjacent sides of the nasal cavity.


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http://www.leffingwell.com/olfaction.htm

Olfactory receptor neurons of the olfactory epithelium project axons

through openings in the cribriform plate to the olfactory bulb. These

projections form cranial nerve I (the olfactory nerve).


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http://www.britannica.com/EBchecked/media/48235/The-olfactory-epithelium-

found-within-the-nasal-cavity-contains-olfactory

Olfactory receptors are bipolar neurons. At their basal ends, they

project cilia into the mucosa, secreted by the epithelial cells and

Bowmans glands.


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http://www.utdallas.edu/~tres/integ/sen6/display10_04.html

The cilia of the olfactory sensory neurons contain the molecular odorant

receptors. Odorants dissolve in the mucosa (perhaps aided by odorant

binding proteins) and activate receptors on the cilia.


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http://www.vetmed.vt.edu/education/curriculum/vm8054/Labs/Lab25/lab25.htm

Electron micrograph of cilia of odorant sensory neurons


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Olfactory sensory neurons turnover within a few months.


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http://www.studyblue.com/notes/note/n/neuro-exam-2/deck/1317431

Odorants evoke depolarization of the receptor cell

dendrites, resulting in action potentials in the axon.


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The molecular receptors for odorants are encoded by ~ 1000 genes in

the mouse. All are G-protein-coupled receptors.

G-protein

Odorant

receptor

G-protein


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Odorant binding activates odorant receptors, resulting in activation of

Golf, adenylyl cyclase and cAMP-dependent cation channels.

Adenylylc

yclase

G-olf

ATP cAMP

Odorant binding


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Each type of odorant receptor is thought to be selective for a specific

molecular moiety on odorant molecules. Thus a odorant may activate

multiple different types of odorant receptors. Our subjective perception of aparticular odor depends on the combination of receptors that are activated.


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http://www.nature.com/ki/journal/v80/n8/fig_tab/ki2011219f1.html

The axons of olfactory receptor neurons terminate in distinctive

synaptic structures in the olfactory bulb, called glomeruli. Most

synapses are on projection neurons called mitral cells. A smaller number

of synapses are on tufted cells. Granule cells provide local inhibitory

connections.


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Each olfactory sensory neuron is thought to express only one type of

molecular receptor. Sensory neurons expressing the same receptor type

are distributed throughout the nasal epithelium; conversely, a single

glomerulus receives input from multiple sensory neurons, all express

the same receptor type.


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http://www.nature.com/ki/journal/v80/n8/fig_tab/ki2011219f1.html

The olfactory bulb forms a map of different types of chemical odorants


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The olfactory bulb receives feedback efferents from ascending

olfactory pathways and from neuromodulatory systems, which mayinfluence the intensity and subjective quality of scents.


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Piriform cortex Amygdala Entorhinal cortex

Thalamus

Hippocampus

Orbitofrontal

cortex

Hypothalamus

Olfactory bulbOlfactory tract

A few of the principle central pathways of the olfactory system

anat 321 the olfactory system

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