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Olfactory
The sense of smell
Olfactory Bulbs
The olfactory bulbs
relay sensory
signals to the
olfactory tract.
small axons from the
olfactory epithelium
synapse with
receptor neurons
and interneurons in
the olfactory bulbs.
• Olfactory receptor neurons extend dendrites
from which several long cilia radiate down into
the olfactory epithelium and into the mucus,
where the air and odorant molecules stimulate
the neuron.
• The receptor neurons synapse with mitral cells at a junction called
the glomeruli.
• Axons from neurons bearing the same kind of stimulus, for example
the smell of perfume, converge on a given type of glomerulus, each
glomerulus receives only one type of odor signal.
• Mitral cells refine the signal, amplify it, then relay the message.
• Periglomerular cells contact multiple mitral cell
dendrites within the glomeruli which provides lateral
inhibition of other glomeruli while allowing excitation of
a specific mitral cell dendritic tree.
• When the mitral cells are activated, impulses
flow from the olfactory bulbs through the
olfactory tracts to the thalamus, hypothalamus,
amygdala, and other regions of the limbic
system.
• In the thalamus it is sent to the piriform lobe of
the olfactory cortex and part of the frontal lobe,
where smells are consciously interpreted and
identified.
• When the impulses are sent to the hypothalamus, the
amygdala and other parts of the limbic system, this is
where the smell innervates emotional responses.
• Smells that are associated with danger, trigger the
sympathetic fight or flight response.
Interesting side note
• The
specialized
olfactory
epithelial
cells
characterize
the only
group of
neurons
capable of
regeneration
Ever wonder why
we sniff?
• Because only 5% of our nostril
is covered with the olfactory
epithelium, we sniff to maximize
the coverage of the air intake
over this portion of our nose as
seen in the diagram to the left.
• Cool huh?
Image bibliography
•
•
http://biology.about.com/library/organs/brain/blolfactorybulb.htm
http://www.emedicine.com/ent/topic564.htm
•
http://www.bartleby.com/107/196.html
•
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/O/Olfaction.html
•
http://www.macalester.edu/~psych/whathap/UBNRP/Smell/nasal.html
•
http://info.med.yale.edu/caim/cnerves/cn1/cn1_1.html