Flashcards in Lecture 3 - Olfactory System Deck (56):
Small, volatile, and hydrophobic molecules
What other epithelium does the olfactory epithelium resemble?
The respiratory epithelium
Describe the olfactory epithelium.
Pseudo stratified columnar epithelium with ciliated apical portion
What 3 cell types does the olfactory epithelium contain? Which cell type has cilia?
1. Olfactory cells***
2. Support cells
3. Basal cells
What sits in between the olfactory cells and the olfactory bulb?
The cribriform plate of the ethmoid bone
Describe the olfactory pathway.
Olfactory cell cilia => olfactory epithelium => olfactory cell axons => ethmoid bone => axon convergence to form CN I (multiple bundles) => glomeruli where CN I synapses with mitral and tufted cells in the olfactory bulb => lateral olfactory tracts => piriform cortex of the cerebrum and amygdala
What is another name for olfactory receptor cells?
Olfactory receptor neurons
How many receptor types does each olfactory cell express?
Can one odorant activate multiple receptor types?
Can one receptor be activated by different odorants?
What gives olfaction a high degree of specificity?
The fact that one odorant can activate multiple receptor types
What gives olfactory cells a high degree of differentiation?
The fact that one cell only expresses one receptor type
What kind of receptors are odorant receptors?
Describe the olfaction transduction pathway.
1. Odorant binds receptor
2. Galpha activates AC
3. AC synthesizes cAMP
4. cAMP activates cyclic nucleotide gated (CNG) ion channels
5. Na+/Ca2+ flow in => depolarization
6. Ca2+ activated Ca2+ activated Cl- channels: Cl-flows out => depolarization until threshold
6. AP in olfactory cell to the olfactory nerve (its axon)
In what structure do the olfactory nerves synapse with the olfactory bulb? Explain in detail.
Glomeruli: one type of olfactory receptor cells synapses with mitral and tufted cells
Describe the symmetry of the olfactory bulb. What does this mean?
Bilateral symmetry so each side has an olfactory tract
What are periglomerular cells?
Cells in the olfactory bulb that sharpen/filter the signal via lateral inhibition
Is there crossing over between the 2 lateral olfactory tracts?
Nope except for the occasional mitral cell collateral
Is the convergence of one type of olfactory cell (aka topography) in each glomerulus preserved in the amygdala?
Is the convergence of one type of olfactory cell in each glomerulus preserved in the piriform cortex?
What are the 4 targets of the olfactory tracts? Which is the main one?
1. Piriform cortex***
3. Olfactory tubercle
4. Entorhinal cortex
Does the thalamus receive information from the olfactory bulb?
Not directly, but some from the amygdala
What are the 3 targets of the amygdala once it receives information from the olfactory bulb?
1. Orbifrontal cortex
What is the target of the entorhinal cortex once it receives information from the olfactory bulb? What is the significance of this?
Hippocampal formation, meaning olfaction is linked to memory structures
Is there a topography of receptors on the olfactory epithelium?
YUP (group in ante/post rows)
Are there more odorants or tastants?
How many types of odorant receptors?
Does the olfactory information pass through the thalamus before reaching the cortex?
What is anosmia?
Lack of olfactory sense that can be temporary or permanent
What are the 2 possible causes of anosmia?
1. Trauma: can tear the olfactory sensory epithelium from the ethmoid bone
2. Illness/blockage of nasal passage due to mucous
What is phantosmia?
What are the causes of phantosmia?
Many from either CNS or PNS
What are pheromones?
Volatile compounds sensed on a subconscious level
Do humans have a vomeronasal organ?
Yes, but it's a residual organ
What do pheromones regulate?
Reproductive behaviors in mammals (e.g. synchronization of menstrual cycles)
How many olfactory sensory epithelium does each human have? Where?
2, one in each nasal cavity above the superior concha
What is another name for the concha bone? Describe it.
Curls like a conch shell
What kind of neurons are olfactory receptor cells?
Bipolar neurons with cilia
On what part of the olfactory receptor cells are cilia located?
The bulbous dendrite
What is the G olf protein?
The trimeric G protein bound to olfactory receptors
What are cyclic nucleotide gated (CNG) ion channels permeable to?
Cations (Na+ and Ca++ flow in mostly)
Where is the olfactory bulb located?
What is the accessory olfactory system? Where is it found?
Only found in non-human mammals
What is the accessory olfactory system pathway?
Odorants => vemoronasal organ => olfactory epithelium => accessory olfactory bulb => medial amygdala => hypothalamus
Does olfaction bypass the thalamus?
What is the difference between the mitral and tufted cells of the olfactory bulb?
- Mitral cells: Principal projection neurons of olfactory bulb and form the lateral olfactory tract
- Tufted cells: local circuit neurons in glomeruli and sharpen sensitivity of individual glomeruli to certain ORNs
What is another name for the piriform cortex?
Primary olfactory cortex
Where is the piriform cortex located?
Medial temporal lobe
What is the role of the olfactory tubercle?
Where is the olfactory tubercle located?
Medial temporal lobe
Where is the entorhinal cortex located?
Medial temporal lobe
What is the orbitofrontal cortex part of?
What part of the thalamus is sent olfactory info from the amygdala?
Medial dorsal nucleus
Is the convergence of one type of olfactory cell in each glomerulus preserved in the orbitofrontal cortex?
What can be said of the neurons of the olfactory epithelium?