Nose:
(olfactory sensation / smell)
-
Receptors
for olfactory sensation are located in the nasal epithelium, which is made
up of three primary types of cells:
-
supporting
cells-- also called sustentacular cells. Columnar epithelium in nature
-
olfactory
cells-- bipolar neurons whose cell bodies are situated between the supporting
cells. The distal or free end of the neuron contains a dendrite which terminates
in a swelling referred to as an olfactory vesicle. From the olfactory vesicle
come six to eight cilia (olfactory hairs), the receptors of smells
-
basal
cells-- located between the bases of sustentacular cells, thought to produce
new supporting cells
In
the connective tissue are olfactory (Bowman's) glands, which produce mucus.
This mucus is carried to the surface by ducts to serve as a solvent for
odoriferous substances. Constant secretion washes the olfactory hairs,
preventing them from sensing the same smell continuously
-
Any
substance, in order to be smelled, must be about to exist as a gas, and
also be water (mucus) and lipid (olfactory hairs) soluable. Although studies
are by no means conclusive, it is currently believed that the nose uses
seven primary smell sensations: putrid, pungent, ethereal, minty, floral,
musky, and camphoraceous. Recent data leads to the expectation that there
may be as many as fifty three more primary scents
-
Unmyelated
axons of the olfactory neurons join the olfactory nerves, which, in turn,
join the olfactory bulbs, running along the
olfactory tract for interpretation in cortex, skipping the thalamus
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