Key takeaways U2 Flashcards
What is one challenge for both taste and smell neurons
how to maintain the integrity of
sensory perception as the receptor cells die and are replaced.
Continuity of perception across time must be maintained - challenge for smell and taste.
What are the requirements for a new taste cell and what is the lifetime of a taste cell
The new taste cells must express the same receptor and the processes must
connect appropriately. TCs live 30 – 60 days
How many odourant receptors does an olfactory neuron express?
Each olfactory neuron (ON) expresses only one odorant receptor
What are the requirements for a new olfactory neuron and what is the lifetime of an ON
New olfactory
neurons must express the same receptor and innervate the correct glomerulus. ONs live 10 – 20
days
Via what cranial nerves does taste info enter the CNS and what does it synapse onto?
Taste information enters the CNS via cranial nerves VII,IX and X and synapses in
nucleus tractus solitarius (NST) in the hindbrain.
Where does the nucleus tractus solitarius (NST) project
NTS projects to insular (taste) cortex via the thalamic nucleus VPM. Insular cortex also projects back to NTS via the hypothalamus and amygdala
(recurrent).
Taste papillae
anatomically arrayed on the tongue/. Taste receptors in fungiform papillae (taste receptors innervated by N. VII) are at the front, and those innervated by
circumvallate papillae (N.IX) at the back. The receptors of N.X that carry taste info are in the epiglottis.
The taste bud includes
taste cells and basal cells (taste stem cells)
The endings of cranial nerves 7,9 and 10 receive input from…
the endings (gustatory afferent axons) receive input from taste cells
How do taste cells respond to tastants?
The taste cell responds selectively to tastants that are salty, sweet, bitter and sour.
Which
tastants directly interact with ion channels?
Salts, acid (sour)
Which are transduced by G protein coupled
receptors?
Sweet, bitter, umami (amino acid)
What do all taste cells release
All tastants release ATP.
What do sour-detecting cells also release besides ATP
The sour-detecting cells also release serotonin.
What molecules help maintain the fidelity of the coupling between taste cells and afferent fibers
maintained by the same molecules that guide developing axons: the semaphorins. Semaphorins support labelled line for sweet and bitter when taste cells turn over. Facilitates aspects of connectivity.
Two potential microcircuits for detecting taste
cross fiber and labelled line
Cross fibre microcircuit
Response in number of different neurons –> one decoder neuron receives converging input from defined set of pre-S neurons –> sensation of sweet.
Labelled line coding
Sweet receptor –> sweet post-S neuron –> CNS
Which microcircuit is used in taste detection
labelled line coding
To determine which cell bodies of which cranial nerve ganglion carry taste information, you could place rhodamine labelled retro beads into the ____________ and look for labelled
cells in the __________ ganglia.
cNST (caudal part of NST); vagal ganglia, geniculate ganglia, glossopharyngeal ganglia
(corresponding?)
Control = infection into cuneate nucleus which has somatosensory info.
The central pathways through which tasted information reaches the forebrain are very similar in rodents and in man except that in humans taste reaches…
the orbitofrontal cortex
Incoming afference from 7,9,10, going into NST, which goes forward into VPMpc (thalamic nucleus), then forward into IC, then in humans goes into orbitofrontal cortex OFC. Has not been detected in the mouse.
In mice, what circuit motif resembles that between the hippocampus and entorhinal cortex?
Recurrent circuit; Recurrent circuits often found in parts of brain involved in memory and learning. Recurrent circuits once activated will continue to activate which maintains the pattern that was initially present in the connection between stimulus and emotional event (between taste and sweet – positive).
What kind of inputs can modify behavior responses to tastants in the brainstem of mice?
Top down innervation; can influence the perception of taste
You can activate bitter and sweet neurons in the brainstem to evoke bitter and sweet perception using…
Channelrhodopsin - channels which are sensitive to light; can open and activate a neuronal response or close and inhibit neuronal response. Effecting output of cells within the CNS.
So, can activate cortical neurons in the labelled line for bitter response, and if bitter tastants are supplied to mouse, bitter response in brain cell is enhanced. If activating neurons in bitter cortex/labelled line, you can suppress response to sweet tastants.