MadSci Network: Anatomy
Query:

Re: Re: Re: Does age affect your olfactory system?

Date: Fri Dec 19 10:39:05 2003
Posted By: Brigitte Todd,
Area of science: Anatomy
ID: 1069997636.An
Message:

Rachael: Wow, that is a big question. I’m going to answer it pretty 
generally and give you some references so you can carry on at your own 
pace. 

Olfaction, the sense of smell, involves the detection and perception of 
tiny odor molecules (odorants). The odorant gets inhaled through the nose 
(or via the oral cavity when eating) and moistened on its way up the 
nasal cavity. Once there, it hits the olfactory epithelium, which is a 
layer of sensory nerve cells (neurons) specifically designed to detect 
odorants. Olfactory neurons have cilia, little hair-like structures that 
have specific receptors for odorants. The upshot of this is that one 
neuron may detect one type of odorant (e.g. a floral smell), while 
another may detect a completely different one (e.g. vinegar). Think of it 
being similar to taste, in that different parts of your tongue detect 
sweet, salty, sour and bitter. The olfactory epithelium neurons then send 
signals to the olfactory bulb, which lies above and behind the nasal 
cavities. The olfactory bulb is organized into groups of neurons called 
glomeruli (think about your tongue again). From there, smell signals are 
sent to the rest of your brain, so you can act on the smell.

Humans don’t compare very well with many other animals when it comes to 
olfaction, but the average person can perceive about 1000 different 
odorants. Remember that olfactory acuity varies a lot between people, so 
there is a large range of what is considered normal. Some people, like 
perfumers, who develop scents, have trained themselves to perceive about 
5000 different odorants. 


As for disorders of olfaction in humans, the most common is specific 
anosmia (anosmia meaning have no sense of smell), whereby the person has 
a lowered ability to perceive a specific odorant, but normal ability to 
perceive others. This is probably due to a lack of the specific receptor 
on the cilia. It’s estimated that up to 20 % of people may have some sort 
of specific anosmia. General anosmia is a complete loss of smell and may 
result from infections or head trauma, or may be congenital. Parkinson’s 
disease sufferers may experience alterations in their olfactory 
capability. Olfactory hallucinations (particularly of bad smells) can 
also occur after epileptic seizures. 

Olfaction in gender and age. It’s generally accepted that women are 
better at identifying odors, at all stages of life. There hasn’t been a 
whole bunch of studies on this though. Have a look at  http://zebra.biol.sc.
edu/smell/ann/myth1.html which addresses sex 
differences and http://zebra.biol.sc.
edu/smell/ann/myth2.html 
which addresses whether olfactory ability declines with age (the general 
feeling is we don’t know very well yet).

Check out  http://www.cf.ac.uk/biosi/staff/jacob/teaching/sensory/olfact1.html 
for a 
tutorial on the sense of smell. If you want books, any standard textbook 
on physiology (e.g. Physiology by Berne and others) or neuroscience (e.g. 
Principles of Neural Science, by Kandel and others) will have a section 
on olfaction (and it won’t be nearly as big as the section on vision!!) 




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