the chemical senses

Question 1

relationship between gustatory and olfactory systems?

Answer 1

gustatory and olfactory systems process in parallel and converge in the CNS

Question 2

what does a salty taste relate to and what is its relevance?

Answer 2

relates to: vital electrolytes
preference: high salt content
relevance: required for physiological processes

Question 3

what does sour taste relate to and what is its relevance?

Answer 3

relates to: acidity (H+ content)
preference: avoid high acidity
relevance: avoid rotting food, injury to GI tract

Question 4

what does sweet taste relate to and what is its relevance?

Answer 4

relates to: sugars
preference: high sugar content
relevance: required for energy, growth

Question 5

what does bitter taste relate to and what is its relevance?

Answer 5

relates to: diverse chemical structure
preference: avoid bitter content
relevance: avoid toxic substances, poisonous

Question 6

what does umami taste relate to and what is its relevance?

Answer 6

relates to: amino acids e.g. glutamate
preference: high amino acid preference
relevance: protein synthesis, neurotransmitters

Question 7

what are lingual papillae?

Answer 7

contain taste buds which are groups of taste cells

Question 8

what are 3 types of lingual papillae

Answer 8

circumvallate = where most of taste cells found, in deep grooves, back of tongue
foliate = grooves similar to circumvallate, side of tongue
fungiform = taste buds on top, no grooves

Question 9

what is a taste bud?

Answer 9

contain ~100 chemoreceptive taste cells
- primary sensory receptors

Question 10

how do taste cells detect tastents?

Answer 10

food is broken down by chewing and dissolves in saliva
- detected by receptors on microvilli on taste cells
chemical signals then trasduced to electrical signals

Question 11

what tastes use ion channels?

Answer 11

• salty
• sour
• bitter

Question 12

what tastes use G-protein coupled receptors?

Answer 12

• sweet
• umami

Question 13

difference in specificity of taste cells vs taste buds?

Answer 13

• each taste cell can only respond to one type of stimuli
• taste buds can have a mix of taste cells (can detect different taste stimuli)

Question 14

how are action potentials triggered in the gustatory system?

Answer 14

gustatory afferent neurons are separate cells to taste cells
requires neurotransmitter release across synaptic cleft

Question 15

major structures of the olfactory system?

Answer 15

• nasal cavity = odorants move up
• olfactory epithelium = contain receptor cells
• olfactory bulb = relays info, many glomeruli
• olfactory cortex

Question 16

stages of olfactory processing

Answer 16

1. odorants move up nasal cavity, dissolve in mucus layer
2. detected by receptors on cilia in olfactory epithelium, location of transduction machinery so converted to electrical signals
3. olfactory bulb receives signals from epithelium and relays info to olfactory cortex

Question 17

what kind of cells are olfactory receptor cells?

Answer 17

bipolar chemoreceptive neurons

Question 18

how can we smell so many different smells?

Answer 18

• humans have ~350 odorant receptor proteins
• each receptor cell expresses one odorant receptor
• one odorant receptor can recognize multiple odorants so combination of odorant allows for many smells

Question 19

how does transduction occur in the olfactory system?

Answer 19

• binding of odorant molecule to odorant receptors causing conformational change in Golf (GPCR)
• alpha subunit activates adenyl cylase which converts ATP into cAMP
• cAMP activates cation channels, Na+ and Ca2+ enter depolarising cell
• Ca2+ gated Cl- channels open (Cl- move out) further depolarising the cell

Question 20

what happens in glomerulus?

Answer 20

• convergence of different receptor neurons
• each glomerulus of the olfactory bulb receives input from only one type of olfactory receptor

Question 21

what do second order neurons project from the olfactory bulbs?

Answer 21

• olfactory cortex = conscious smell
• hippocampus = olfactory memory
• emotional responses
• hypothalamus = sex and neuroendocrine
• reticular formation = visceral responses (e.g. gagging)