Olfactory The sense of smell

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