Olfactory system- Johening Flashcards
it is important to study the olfactory system because…
a. in many neurodegenerative diseases and especially Alzheimer’s disease, olfactory symptoms ofter occur prior to onset
b. to understand perception of food and consumption of food
c. brain circuitry underlying flavour perception is altered in obese people
d. all of the above
d
what is the difference between orthonasal and retronasal smell?
Orthonasal smell: direct nasal inhalation of air particles from the environment (we breath in air and sniff food and environment).
Retronasal smell: food consumed by the mouth is chewed–> releases volatile molecules which enter the nasopharynx and travels up to the olfactory epithelium and from there to the olfactory bulb and cortex.
- retronasal smell is much more important for humans because of food perception
why does hot coffee taste better than cold coffee?
volatile layer of HOT coffee molecules travel to the nose much faster and in larger amounts because the high temperature increases broconian motion and diffusion of molecules
what is the advantage of using miniature head microscopes combined with GRIN-lense? what is the procedure?
Obesity is a universal problem which is affecting many people all over the world and our understanding of the neuronal mechanisms underlying overeating and obesity is limited.
–> this method allows to look at the cell assemblies that are active while the mouse is eating, and the activity is connected to the sensor at the feeder so number of licks consumed is recorded too.
Procedure:
- the method images the mouse’s brain while its moving freely, by putting a huge glass prism in the cortex until the puriform cortex is reached.
- behavioural paradigm: sensory specific satiety - mouse drinks a lot of milkshake in the first trial and consumption decreases in the next bouts, because cells adapt to the smell of milkshake after the first trial –> signals satiation
describe the physiological reaction to smell (steps)
- odourant molecules go through the nose and bind to 7-TM-G-protein
- conformational change of G-protein
- ß-gamma and G-protein components are dissociated
- G-protein binds to adenylate cyclase
- cAMP channel opens
- Na+ and Ca2+ flow in and depolarise the cell
which of the following statements about olfactory receptor neurons (ORN) is/are correct?
a. ORNs can express various types of olfactory receptors
b. ORN are specific to smell types like ‘coffee’ or ‘chocolate’
c. ORN are not specific to single molecules but rather they react to chemical groups
d. odourants activate different ORNs in the same intensities
c
which of the following statements is WRONG?
a. odour coding starts already at the level of nasal mucus
b. subtle structural changes result in fundamentally different smells
c. different odourants activate different receptors at changing intensities
d. odour coding starts in the olfactory cortex
d
olfactory projection…(which of the following statements is/are correct?)
a. ORN are everywhere but they converge and project to 2 specific glomeruli in the olfactory bulb
b. this convergence is acquired during childhood (exposure)
c. odours are deconstructed to their components in the olfactory bulb, and then reconstructed and mixed in the cortex
d. single glomerulus project to a single neuron in the olfactory cortex
e. neurons in the olfactory cortex respond to groups of glomeruli.
a, c, e
what is the population code?
population code is a term that describes odour processing of olfactory signals in the cortex.
- -> odours are deconstructed to their chemical components in the olfactory bulb, but when the info is projected to the cortex the signals are mixed.
- -> large neuronal cell assemblies in the olfactory bulb respond to groups of glomeruli–> population code
- -> distinction between odour components is lost
how can you empirically test if it is possible to distinct between components of smell? (study + results)
- 2 test groups: wine experts and naive subjects
- test: subjects exposed to a number of smells with increasing complexity–> asked to identify the smell and components
- results: very small difference between the groups as complexity of the smell goes beyond 3-4 components.; but experts perform better in deconstructing simple smells.
how are cell assemblies formed in the olfactory cortex, and what are the benefits of assembly formation?
- external stimulus
- -> 2. activation of neuronal population by stimulus
- ->3. activity continues after stimulus is gone (creation of engram)
- -> 4. Hebbian modification strengthens reciprocal connections between neurons in the same assembly
- -> 5. strengthened connections contain the engram for the stimulus
–>When partial stimulus comes–> partial activation of the assembly lead to activation of the entire assembly (representation of the ‘full’ stimulus
Advantages:
- even parts of the olfactory stimulus can activate the assembly and generate a behaviour
- good for dangerous smells or smells that trigger memories - we can recognise the dangerous smell even when it is partial or low intensity and still react to it.
- pattern completion- reconstruction of engrams
what are sister cells?
sister cells are group of mitral cells that send apical dendrites to the same glomerulus
what are the advantages of the convergence of cells in the olfactory bulb?
- olfactory neurons keep rebuilding (consistent, 2 week turnover) and by converging into the same glomerulus, centrally, they increase the stability of the system, as they wire up and the same smells can be identified easily.
- optimisation of the detection of smells at low concentrations
which of the following statements is/are correct?
a. glomeruli have a Ih pacemaker current (H-channel) that activate upon hyperpolarisation
b. H-channel resets the neuron to a different potential - hyperpolarisatio and direct depolarisation after (Sag current)
c. H-channel is activated upon depolarisation
d. H-channel decreases response at the dendrite and increases input at the soma
e. cells from different glomeruli the H-current varies dramatically in comparison to sister cells.
a, b, e
which of the following statements about information coding of smell is/are correct?
a. number of generated APs decreases with increasing odour concentration
b. changes in firing rate occurs in the bulb, and it is the strongest during adaptation to smell.
c. information coding depends on spatial population dynamics but not on temporal population patterns.
d. information coding contributes to generation of oscillations by the olfactory bulb.
e. all of the above
b, d
