welcome in this lecture we will be
learning about the special senses
the special senses include the sense of
smell
taste vision hearing
and also your sense of equilibrium
starting with our sense of smell also
referred to
as olfaction smell is considered a
chemical sense the human nose
contains 10 to 100 million receptors
for smell in the olfactory epithelium
which is located in the superior part of
the nasal cavity
the olfactory epithelium covers the
interface of the cribriform plate of the
ethmoid bone of the skull and extends
along the superior nasal concha
depicted in the figure we see the path
of inhaled air
comes through the nasal cavity the
olfactory epithelium
then contains ciliated olfactory cells
and producing olfactory gland cells
and also other cells and connect the
nasal cavity
to the olfactory cranial nerves
there are three types of cells that are
responsible for olfaction
we have the olfactory receptor cells
which are first
order bipolar neurons with an exposed
knob shaped dendrite and an axon that
travels through the cribiform plate of
the ethmoid bone
and end at the olfactory bulb
we also have supporting cells which are
going to support and nourish
our olfactory receptor cells and finally
we have
basal cells which are stem cells that
are used to generate
new olfactory cells
the supporting cells are going to be
located in the mucous membrane lining of
the nose
again these are used for the physical
support
nourishment and as well the electrical
insulation for our olfactory receptor
cells
our basal stem cells are able to undergo
mitosis
and are there to replace old and dead
olfactory receptor cells
also along with the three cell types
that are responsible for olfaction
the olfactory epithelium also contains
olfactory glands that are known as the
olfactory glands or
bowman's glands these are going to
produce
mucus that is used to dissolve odor
molecules
also called odorants so that they may be
transduced
olfactory transduction is the binding of
an odorant molecule
to an olfactory receptor protein
olfactory transduction begins when an
odorant
binds to the olfactory receptor cells
this leads to a chemical reaction
involving cyclic
amp and causes depolarization
the binding of an odorant molecule to
the g-protein-coupled receptor found in
the membrane
activates the g protein which then binds
to
the adenylyl cyclase enzyme
the adenylyl cyclase is a membrane
protein that catalyzes the reaction
converting atp to cyclic amp
from there cyclic amp binds to
and opens cation channels in the
olfactory receptor cell
this causes an influx of sodium and
calcium
which leads to the depolarization of the
receptor cell
this causes an action potential to
propagate
to the primary olfactory area of the
cerebral cortex
all of this is going to happen by way of
the olfactory nerve
the human nose has about 10 million
olfactory receptors there are
approximately
400 functional types of olfactory
receptors
each type can only react to a select
group of odorants and only one type is
found
in each of our receptor cells
the receptors and the nasal mucosa
are going to send impulses along the
branches
of the olfactory nerve through the
cribiform plate
where they synapse with the axons
and converge into mitral cells
axons of the mitral cells form the
olfactory tract
and impulses travel along this olfactory
track
and some of the axons are also going to
travel
to the primary olfactory area of the
temporal lobe of the cerebral cortex
for interpretation
from the primary olfactory area a
pathway is going to extend by way of the
thalamus
to the orbital frontal cortex in the
frontal lobe
where odor identification and
discrimination is going to
occur other axons of the olfactory tract
go to the limbic system this is going to
be responsible for our emotional
response to certain odors such as
feeling happy
when you have the smell of brownies or
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