ANAT 321 the Olfactory System
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Transcript of 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