Taste and Smell Flashcards
What is the difference between the othonasal and the retronasal pathway?
Orthonasal is what comes through the nose.
Reteonasal pathway is from the back of the pharynx.
How does the olfactory epithelium work?
Sensory neurons project within the epithelium and lie onto of the epithelium covered in a layer of mucus.
This makes the neuroses susceptible for damage so loss of smell is quite a common occurrence. This can be due to taking in fumes or from a concussion knock on the head affecting the olfactory bulb.
Loss of smell leads to an altered taste.
What are nasal secretions made by?
- Made by Bowmans glands
- Controlled by nerves (autonomic) and steriods
- Contains mucins, secretory antibodies and other proteins
- Contains odorant binding proteins - proteins that can pick up different smells and help transport them through the mucus, to the receptors on the neurons.
What happens when an odorant hits an odorant receptor?
cAMP mediated signalling pathway.
Odorant binds to the G protein coupled receptor.
Activation of adenylyl cylase to make more cAMP.
cAMP goes onto activate the sodium/calcium channel.
Activation of the choride channel causes depolarisation of the neuron to continue the signal on.
Switching off pathway = enzymes to pump calcium out of the neuron, reabsorption of calcium into the mitochondria. This sends the neuron back to resting state.
Extra cellular proteases can get pushed out the cell and will attach the odorant binding proteins on the receptor.
Where do the taste buds found on the tongue?
Some taste buds in the fungiform papillae on tip of tongue but most are located within the circumvillate papillae and the foliate papillae.
Lingual salivary glands here are serous, lingual lipase is an important constitute to remove fat on the tongue.
What are the 5 cell types of the taste bud?
Type 1 = glial cells which cover type 2 and 3
Type 2 = receptors to sweet, bitter and umami
Type 3 = detects sour and salt
Type 4 = basal cells
Type 5 = marginal cells
Give some details on the taste receptors for type 2 and type 3 cells
Type 2 have G protein receptors which either homo-dimers (usually for bitter taste) or heterodimers for different tastes (sweet and umami taste).
30 receptor types for bitter taste but only a few for sweet and umami.
Type 3 cells - 1 channel for sour and one for salt.
For sour, it has a receptor potential type channel for sending protons.
For salt, there is a sodium channel to pick up sodium ions.
Explain how signalling work for type 2 cells
This is an intracellular calcium pathway.
Have G protein receptor on surface. One agnostic binds, get a production of PLC to the endoplasmic reticulum causing calcium ion release here.
Increase in calcium intracellularly activates other channels to allow sodium ion influx. This causes the release of the NT (ATP in this case) across to the neuron which depolarises and sends information to the brain.
What is the difference between type 2 and 3 signalling?
Type 3 doesn’t have the increase in calcium intracellularly.
How is taste processed in the brain stem?
In taste, the tongue is innervated by the 7,9 and 10 cranial nerves. These attach into the brain stem and sends signals into the cortex. These signals get modulated by many places in cortex (amygdala, hypothalamus, gustatory cortex). These send signals back to salivary glands to secrete more saliva e.c.t.
How is smell processed in the brain stem?
Central processing for smell is different as the olfactory neurons pass through directly into the brain and dont go via the brain stem.
These direct projections means that smell may be more likely to lead to more memories than taste does.
