olfactory/gustatory systems

Question 1

difference between labelled line code and combinational code

Answer 1

labelled line = linear
ie. sweet->->->sweet
combinational = complex
ie. inhibition and stimulation -> sweet

Question 2

olfactory sensory transduction

Answer 2

second messengers amplify sensory signals
olfactory neurone → cilia → olfactory receptors (GPCR) → AC → cation channels

Question 3

olfactory receptor features

Answer 3

in humans = 300
- each receptor responds to different set of queues
- As olfactory sensory neurons mature, they narrow down to express a single olfactory receptor each
- all axons expressing same receptor converge onto same glomerulus

Question 4

how do sensory neurones transfer info to second order neurones

Answer 4

glomeruli
sensory neurones converge and send signals to one projection neurone/glomerulus

Question 5

function of first relay synapse

Answer 5

• adaptation synapse
  
  • emphasises start of odour
• convergence of sensory neurones onto second order neurones
  
  • reduces noise
  • strengthens weak response

Question 6

functions of lateral cross-talk

Answer 6

• gain control
  
  • sensitive to weak and strong odours
  • uses other neurones to suppress response to detect increases in intensity
• de-correlation
  
  • make responses of neuronal population to different odours as different as possible
  • makes some odour channels more distinct

Question 7

brain structures involved in olfactory processing

Answer 7

• olfactory bulb → piriform cortex (learning/association)
• cortical amygdala
• lateral horn

Question 8

innate behaviours easy to predict?

Answer 8

easy to predict due to wiring

Question 9

learned behaviours easy to predict?

Answer 9

hard to predict as is wired during development → rando

Question 10

olfactory simple search behaviour

Answer 10

• straight toward smell if +ve
• opposite direction if -ve⇒ run or tumble behaviour

Question 11

olfactory complex search behaviour

Answer 11

• +ve odour = flies upwind
• losing odour = wait before turning
• when source is reached use other sensory cues to reach target
• Moving your head around lets you sample a larger space and generate fast changes of detected odour concentration (set behaviour according to adaptation statistics of sensory neurons)

Question 12

taste transduction

Answer 12

• salty = Na
• sour = protons (acid)
• ion channels = amplification ⇒ cranial nerves ⇒ solitary nucleus ⇒ thalamus

Question 13

lateral inhibition of taste transduction

Answer 13

• e.g salty = inhibition of sweet and vice versa
• why? → poison = suppress other tastes to highlight danger

Question 14

Different tastes activate different parts of the brain

Answer 14

• hotspots of insula responsive to specific tastes
• optogenetically activating ‘sweet’ or ‘bitter’ areas of insula makes mice approach or avoid the stimulus