slide 1 smell olfaction brings both good news and bad news pheromones smell— a mode of...
Post on 16-Dec-2015
212 Views
Preview:
TRANSCRIPT
Slide 1
Smell
Olfaction brings both good news and bad newsPheromones
Smell— a mode of communication as well as of detecting environmentImportant signals
Reproductive behaviorTerritorial boundariesIdentificationAggression
Role of human pheromones ; not as prominent as in other animals but still play roles unwittingly!
Slide 2
Smell
The Organs of SmellOlfactory epithelium
Olfactory receptor cells : 4-8 wks life cycle
Supporting cells : like glia, help producing mucus Basal cells : olfactory neurons source (stem cell)
(Cranial nerve I)
Slide 3
SmellThe Organs of Smell
Mucus layer : water base with mucopolysaccharides antibodies - critical defense en route to brain various enzymes odorant binding proteins - concentrate odorants
Olfactory acuity : The size of olfactory epithelium and the number of olfactory receptors
e.g. dog vs human : 170 cm2 vs 10 cm2, 100 times more receptors per sqarecentimeters
Vomeronasal organ : pheromone sensing organ project to accessory olfactory bulb
Slide 4
SmellOlfactory Receptor Neurons
Olfactory Transduction • Cl- channel opening mediate outflow of chloride ions :Unusually high intracellular Cl- conc. enhance depolarization (in contrast to what happens in other neurons) • Termination of olfactory sensation :
Odorants diffusion Degradation (scavenger enzymes) 2ndary signalling pathway to end the transduction – adaptation (even when odorants still be around)
Slide 5
Smell
• Cl- channel opening mediate outflow of chloride ions :Unusually high intracellular Cl- conc. enhance depolarization (in contrast to what happens in other neurons) • Termination of olfactory sensation :
Odorants diffusion Degradation (scavenger enzymes) 2ndary signalling pathway to end the transduction – adaptation (even when odorants still be around)
Olfactory Receptor NeuronsOlfactory Transduction
Slide 6
Olfactory TransductionOdorant receptors
• More than 1000 genes in rodents (Linda Buck and Richard Axel)
—The largest gene family in mammals
—~350 in human• Genes are scattered (in clusters)
about on the genome• Each Olfactory neurons seem to
express single odorant receptor gene : choice mechanism unknown!!.
• Zonal and random (within a zone) expression
— each zone express a different, nonoverlapping subset of receptor genes
Smell
Slide 7
Olfactory Transduction
Smell
• VNO has its own receptors : — ~300 in mice, 5 in humans— Structurally different from
odorant receptors— Ligands are largely unknown
• Unusual cAMP gated channels are evolutionarily conserved : Used in the visual transduction as well
• Recent finding suggests both olfactory system and vomeronasal system regulate behavioral outcome such as reproduction
• Population coding : both odorant type (which cells) and strength (how active) are used to classify the odors
Slide 8
Central Olfactory Pathways
Smell
• Each Ob has about 2000 glomeruli
• Each glomerulus contains about 25,000 primary olfactory axons and dendrites from about 100 second-order olfactory neurons (Mitral cells)
Slide 9
Central Olfactory Pathways
Smell
Slide 10
Central Olfactory Pathways
Smell
Precise mapping :• All axons from neurons that express one particular receptor gene converge onto glomeruli on each bulb• Each glomerulus receives input from only receptor cells of one particular type• Symmetrical positions• Consistent positions of glomeruli from one mouse to another
Intricate circuitry :• Excitatory and inhibitory connections
-Within glomeruli-Among glomeruli-Between obs
• Broad categorization of odorant signals might be done at this level
Slide 11
Central Olfactory Pathways
• Direct projections to cortex (OB-OC):unique to olfactory system• Paleocortex VS. Neocortex• Multiple projections (from OB) to many brain structures• Direct and widespread influence on odor discrimination,
emotion, motivation, memory..• OB-OT-Medial dorsal nucleus of thalamus pathway may be
responsible for the conscious perception of smell, while connections to amygdala and entorhinal cortex may be involved in the affected (associated) components of olfaction such as aversiveness
Smell
Slide 12
Slide 13
Spatial and Temporal Representations of Olfactory Information
Olfactory Population Coding• Combinations increase resolutions
Olfactory Spatial Maps• A sensory map is an orderly arrangement of neurons that
correlates with certain feature of the environment• Reproducible spatial pattern in the system that no where
information is needed- WHY?- Discrimination among different chemicals?- Just for the efficiency? - Easier communications with
neighbors- Systemic relationships between chemicals and map
positions?
Smell
Slide 14
Spatial and Temporal Representations of Olfactory Information
Chemotopy
Smell
Slide 15
Spatial and Temporal Representations of Olfactory Information
ORN receptive fields and acuity
Smell
Slide 16
Spatial and Temporal Representations of Olfactory Information
Temporal coding
Odors are inherently slow stimuli - The timing of odors
is not so important but the quality of odors is
Oscillation between ob and cortex when odors are
present - imply the presence of temporal odor code
ORNs responsive to a particular odor display a wide
range of temporal spiking pattern
In honeybee expts, ablating the synchrony of firing
brought about a loss of bee’s ability to distinguish
between similar odors ( not between broad category of
odors)
Smell
Slide 17
Spatial and Temporal Representations of Olfactory Information
Temporal coding hypothesis
Smell
top related