Olfaction And Taste Flashcards
Where are olfactory receptor neurons located?
In the mucosa lining the upper nasal cavity
What are chemical senses?
What are the three main types of chemical senses?
Highly conserved sensory system that allows the identification of chemicals in the environment.
- Olfaction- substances dissolved in the air
- Gustation (taste)- substances that are water and fat soluble
- Trigeminal “irritant” detection- noxious, injurious chemicals
Where are nocioceptors located?
Mucosa of the oral cavity, sinonasal tract and eyes
What are the volatile molecules called that the olfactory system detects?
What happens to the sensitivity and specificity of the olfactory system as we age?
Odorants
Diminishes
What is the most peripheral component of the olfactory system?
The olfactory epithelium- a component of the mucosa that occupies the lining of the upper nasal cavity
What type of neuron is the olfactory receptor neuron (ORN)?
Where are it’s dendrites located?
How many ORNs are in the olfactory epithelium?
A specialized bipolar neuron
It’s dendrites extend into the nasal cavity where they form knobs with microvilli that extend into a layer of mucus that covers the olfactory and adjacent respiratory epithelium
5x 10^6
What are the major cell types in the olfactory epithelium?
ORNs
Basal cells
Supporting cells
Trigeminal cell nerve endings
Why do ORNs have a limited life span?
How does the body take care of this fact?
Because of the exposure to injurious molecules in the inhaled air.
ORNs continue to regenerate after birth from stem cells
What is located in the ORN microvilli that allows it to bind to proteins in inhaled air?
What is the structure of this molecule?
Specific odorant receptor proteins which are G-protein coupled and cell membrane spanning
They have an odorant binding domain on the cell surface, 7 transmembrane domains and an internal cAboxy terminus that interacts with ORN-specific cytoplasmic G-proteins
When an odorant binds the specific odorant receptor protein, what is the sequence of events?
- The odorant binds
- ORN-specific adenyl cyclase increases local cAMP
- CAMP opens ion channels (Ca) in the ORN dendrite
- AP is generated
- How many odorant receptor genes are there?
- How many different odorant receptor proteins are actually expressed in humans?
- How many odorant receptor proteins does each ORN express?
- 950
- 400
- One and only one SPECIFIC odorant receptor protein
How are we able to distinguish such a wide range of odorants in the environment?
Even though each ORN has only one type of specific odorant receptor protein, each SORP can bind multiple odorants and each odorant molecule can bind to different SORPs.
After an AP is generated in the ORN, what is the sequence of events?
- The AP travels upward through the cribriform plate along the ORN axon.
- ORN axon crosses the cribriform plate in filia (olfactory nerve proper)
- ORN synapse with mitral cells in the olfactory bulb glomeruli
- Mitral cells interact with local neurons in the olfactory bulb
Where are mitral cells located?
What are the afferents?
What are the efferents?
Mitral cell dendrites are located in the olfactory bulb glomeruli
They receive signal from filia (true olfactory nerve)
They project to:
Tufted cells
Periglomerular cells
Granule cells
What is the only sensory system that goes to the cortex BEFORE synapsing on the thalamus?
Olfactory
Each mitral cell receive signal from approx _______olfactory filia (ORNs).
They all express _______________, though.
- 1000 ORNs
2. The same specific odorant receptor protein
Each olfactory bulb glomeruli contains the dendritic process of (1-how many) (2-what type of cell)?
25 mitral cells
Overall, an olfactory bulb glomerulus responds to only a single odorant but input from ________ORNs.
25,000
What is the anterior olfactory nucleus?
What are the afferents?
What are the efferents?
Neurons along the olfactory tract that receive input from ORN collateral branches.
They send axons to bilateral olfactory bulbs to facilitate bilateral processing of olfactory stimuli
What are the bundles of mitral cell axons called?
Where do a small fraction of mitral axons go?
Where do MOST mitral axons go?
Olfactory tracts.
Some axons go posteriorly to synapse with neurons in the olfactory tubercle
Most bypass the tubercle and go to other cortical areas through the lateral olfactory tract to go to the piriform complex, entorhinal complex and Amygdala
Where do MOST axons from the lateral olfactory tract make synaptic connections?
Neurons in the piriform cortex -a three layer primitive area on the medial surface to the parahippocampal gyrus near the optic chiasm
What is anosmia?
Olfactory injury that can be acquired or hereditary
Acquired: Parkinson’s, trauma, infection
Where do neurons from the piriform cortex project? (6)
- Amygdala and entorhinal cortex (which receive direct mitral input as well)
- Hippocampus -odor and memory
- Hypothalamus- odor and food intake/survival
- Thalamus- dorsomedial nuclei limbic influence of cognition/emotion
- Orbital frontal cortex- limbic cognition and emotion
- Insular cortex
What are the molecules that are detected by the gustatory chemical sense?
What cells do they interact with and where?
Tastants- molecules dissolvable in water and fat.
Taste cells- a neuroepithelial cell on the tongue and mucosal surfaces of the oral cavity and orpharynx
