Gustatory and Olfactory Receptors and Pathways Flashcards
What are the three types of papillae which contain taste buds? The one that is used for friction?
- Fungiform - mushroom shaped ~4 buds
- Vallate - moat-shaped
- Foliate - folds on side of tongue
Friction - filiform
What are the four cell types of the taste bud and what do they do?
- Parietal cells - give rise to sustentacular + basal cells
- Basal cells - give rise to gustatory cells
- Gustatory cells - chemoreceptor cells on apical membrane
- Sustentacular cells - supporting cells
Why do old people lose their sense of taste?
Lose taste buds throughout life at a rate of 1% per year
What types of synapses do nerve fibers make with gustatory cells?
Chemical synapses
What type of receptor does each taste sense use?
Sweet - GPCR Sour - ionic Salty - ionic Bitter - GPCR Umami - GPCR
What nerve innervates the taste buds on the epiglottis?
CNX
What are the relevant ganglia for taste perception? Where do their roots enter?
Anterior 2/3 - Geniculate ganglion of 7 - cerebellopontine angle
Posterior 1/3 - Petrosal ganglion of 9 - postolivary sulcus, rostral medulla
Epiglottis - Nodose ganglion of 10 - postolivary sulcus, mid medulla
What is the gustatory nucleus?
Rostral 1/2 of solitary nucleus, where 7, 9, 10 central processes synapse for taste.
What are the reflex pathways for gustation?
Rostral solitary nucleus gives second order taste fibers which synapse bilaterally to inferior salivatory nucleus and superior salivatory nucleus.
What is the superior salivatory nucleus?
Nucleus which controls salivation for submandibular, sublingual, and lacrimal glands
What is the inferior salivatory nucleus?
Nucleus receiving bilateral contributions for salivation from the parotid gland
What is the course of the second order neurons of the taste pathway?
Ascend from the rostral solitary nucleus through the central tegmental tract to the most medial part of the VPM thalamus, where they synapse on tertiary taste neurons
What is the course of the third order neurons of the taste pathway?
Axons from VPM thalamus go through internal capsule + corona radiata. There are two primary cortical taste centers.
- Parietal operculum - ventral aspect of postcentral gyrus
- Anterior portion of insular cortex
Where does crude awareness of taste vs fine discrimination occur?
Crude awareness = thalamus
Discrimination = cortical levels
What is the general function of the insular cortex for olfaction and taste?
It is the place where both oolfactory and taste sensation are integrated
What is the word for distorted sense of taste?
Dysgeusia
What is the primary olfactory neuron called and where is it located?
The olfactory bipolar neuron. Located in the superior nasal concha and adjacent nasal septum.
What is the turnover rate of gustatory cells and olfactory bipolar neurons? Where do they come from?
Gustatory - 7-10 days
Olfactory bipolar - 30-60 days
They are derived from basal cells
Where do the bipolar neurons processes go?
Dendrites - to apical epithelial surface, forming dendritic bulb
Axons - joins the olfactory nerves
What does the dendritic bulb do?
Has ciliary projections which project into the covering film of watery mucus
What is the receptor type of olfaction and how do we detect such a wide range of smells?
There are over 1000 different receptor types, and each cell only expresses one, so there is a wide diversity.
Receptor type = G-protein coupled receptor.
What is an olfactory filum? Where do they terminate?
A collection of 10-100 unmyelinated axons of olfactory bipolar neurons which are organized by Schwann cells. They project through the cribriform plate of ethmoid bone and terminate in olfactory bulb.
What is the olfactory tract vs olfactory nerve?
Nerve - prior to reaching olfactory bulb, the collection of all olfactory fila
Tract- collection of axons from the olfactory bulb (second order olfaction neurons)
What is the neuron type of the olfactory bulb?
Mitral cell - receives input at glomeruli from olfactory bipolar neurons at apical dendrites
What are periglomerular cells and what neurotransmitter do they use?
They are for lateral inhibition - that release GABA at the glomerulus (synapse between mitral cell and olfactory bipolar neuron)
What are granular cells and where do they synapse? What neurotransmitter do they use?
Synapse on the secondary dendritic processes of mitral cells with dopamine neurotransmitter. Dopamine is inhibitory, as these cells function in lateral inhibition from contralateral anterior olfactory nucleus.
What is special about mitral-granular synapses?
These are dendrodendritic synapses. The mitral cells can activate these to laterally inhibit offline mitral cells.
Where does the olfactory tract travel?
In the olfactory sulcus, just lateral to the gyrus rectus and medial to the orbitofrontal gyrus.
Where does the olfactory tract divide?
Just anterior to the anterior perforated substance, into small medial stria and prominent lateral stria
What does the medial olfactory stria hold?
Axons from anterior olfactory nucleus crossing the anterior commissure for feedback regulation of contralateral olfactory bulb (directly to granular cells or relay to contra AON),
AND
Mitral axons projecting to anterior perforated substance and septal area, for the limbic system
What is the function of the septal area?
Receives medial olfactory stria, it is the pleasure center for the limbic system for smells
What projects to the primary olfactory cortex, what is it, and what is it for?
The lateral olfactory stria project to the piriform cortex, which is for recognition or awareness of smell
What is the function of the corticomedial nuclei of amygdala?
Receives contribution from lateral olfactory stria, this controls SANS and PANS responses to unpleasant odors, which are important in regulation of food intake
What is the secondary olfactory cortex?
Entorhinal cortex, it projects to amygdala, hippocampal formation, insular cortex, and orbitofrontal cortex thru DM thalamus
What projects to and what is the function of the basolateral nuclei of the amygdala?
Primary and secondary olfactory cortices. Functions in emotional reaction to olfactory impulses, i.e. smelling smoke
What is the function of the hippocampal formation?
Receives input from secondary olfactory cortex for smell memory, and limbic center
What is the function of the insular cortex for olfaction?
Integration with taste impulses
What is the tertiary olfactory cortex? What does lesion cause?
Orbitofrontal cortex -> lesion causes impairment of odor discrimination.
Entorhinal cortex must relay through DM thalamus.
