Transcript The average human being can recognize up to 10000 different odors

SENSE OF SMELL
Why is smell called a chemical sense?
 Because it
involves the
detection and
perception of
chemicals (odor
molecules –
odorants) floating
in the air.
What is the olfactory system
responsible for?
 Main function is
sensor of the
environment
 Reception,
perception, &
identification of
odorants
What associated functions does the
olfactory system have?
 Sexual behaviors
 Hormone release, choosing a mate
(reproductive state and availability)
 Social behaviors
 Territoriality, aggression,
identifying children
 Smell + Taste = Flavor!!
 Flavor is up to 80% smell
What are neurons?
 Specialized
sensory
nerve cells
How many odors can the
olfactory system recognize?
The average human
being can recognize
up to 10,000
different odors
What is the olfactory epithelium
(lining)?
 A layer of
specialized
(for olfaction)
tissue
covered with
a mucous
membrane
Where is the olfactory epithelium
located?
 In your nasal cavity,
beyond your nostrils
 In humans, about the
size of a postage stamp
What is located on the olfactory
epithelium?
 Covered with olfactory receptor cells (olfactory
neurons, or ONs)
 Humans:
 Have more than 100 million ONs
 Each ON contains one receptor
 Have about a thousand of different odor
receptors
 Combination strategy: odor molecules are
recognized by more than one receptor and
most receptors recognize several odors
What is located on
olfactory receptor
neurons?
(Structure of Olfactory
Receptor Cells/Neurons)
 Dendrite covered
with small hairs
called cilia on one
side
 Axon on the other
side
What do these olfactory neurons do?
 Polarized: One side is specialized
for chemical detection and the other
for signaling
 Cilia on dendrite end (receptor):
 Actual binding of odorants
 Axon end:
 Nerve fiber that connects with and
sends smell information to the
olfactory bulb
Notes: Signal Transduction
 Once the receptor has bound an
odor molecule, a cascade of
events is initiated which transform
the chemical energy in binding
into a neural signal (that is, a
change in membrane potential)
Notes: Signal Transduction
1. Binding activates olfactory G protein
2. An influx of Na+ and Ca+ (also exit of
Cl-)causes the inside of the cell to become
less negative
1. Eventually the change in charge reaches
threshold and an action potential is
generated (message is sent)
2. The action potential then moves along the
axon (message is “in the mail”)
3. The axon synapses with the neurons in the
olfactory bulb (message is received)
What is special about olfactory
neurons?
Unlike other types of nerve cells,
they can be and are replaced
Regenerate every 30-60 days
Where is the olfactory bulb located?
 Just beyond the
nose (brain
structure)
What are glomeruli?
 Specialized structures
(collections of cells)
located in the olfactory
bulb
 Where neurons with the
same kind of odor
receptors converge
 It is here where olfactory
neurons connect with
other types of neurons
(mitral cells)
 Mitral cells carry info to
other parts of the
olfactory system
How does the olfactory
system identify a unique scent?
 All information sent from olfactory
epithelium (from all olfactory receptor
neurons) is organized in the olfactory bulb
 The organization produces a pattern
(called a spatial map) in the olfactory bulb
characteristic for a given odorant or blend
of odorants
Where does olfactory information travel?
 Brain's cortex (in cerebrum),
or outer layer, where
conscious thought occurs.
 Hypothalamus, which controls
sexual and maternal behavior.
 Limbic system
 Information is carried along nerve fibers
What can damage an individual’s
sense of smell?
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Chemicals
Aging
Radiation
Hormonal disturbances
Sinus infections
URI
Dental problems
Anosmia: sinus disease, growths
in nasal passage, viral
infections, head trauma
What is the limbic system?
 The limbic
system is
involved with
emotional
behavior and
memory.
What is the relationship between
smell and the limbic system?
 Smell information is sent to brain
structures of the limbic system
 Amygdala: intense emotion
 Hippocampus: associative learning
 A scent can “recall” the memories &
feelings associated with it
 (Long term & emotional memory)
Summarize the path odor molecules take
from inhalation to behavior.
 Odor molecules in air 
olfactory epithelium  olfactory
receptor neurons (recepted by
cilia)  axon of olfactory
neuron  glomeruli in olfactory
bulb (organization, recognition,
and identification of scent) 
other parts of the brain
Other Stuff: Olfactory System
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Largest gene group
Associated with Alheimer’s, Parkinson’s, OCD
Women have keener sense of smell
People recall smells with a 65% accuracy after
a year, while the visual recall of photos sinks to
about 50% after only three months
 A team of researchers found that when people
were in a room recently spritzed with a citrusscented cleanser, they behaved more fairly
when playing a classic trust game. In another
experiment, the smell of cleanser made
subjects more likely to volunteer for a charity.