Chemical Sense

Question 1

How are taste cells distributed

Answer 1

The distribution is relative, not absolute
Areas are more sensitive than elsewhere but it is still possible to detect flavours within all the regions

There is a concentration threshold for each receptor for the substance they are most sensitive for, but at high concentrations they can detect all flavours

Question 2

What increases the surface area for recognising taste detection

Answer 2

Papillae and each papillae has 1-several hundred taste buds which have 50-150 taste receptor cells each

Question 3

Are taste cells sensory neurones

Answer 3

NO they look like them but aren’t them. As they do synapse but do not fire an AP

Question 4

Where is the sensitive part of the taste cell

Answer 4

Apical end it has thin extensions - microvilli which project into a taste pore they are exposed to the contents
they form synapses with the end of gustatory efferents near the bottom of the taste bud.

Question 5

Depolarisation causes

Answer 5

Opening of the Ca2+ channels which cause NT release.

Question 6

Mechanism of taste transduction

Answer 6

Chemical binds -> depolarisation -> voltage gated Ca2+ channels open -> Ca2+ entry -> NT released -> excites sensory neurone -> AP

Question 7

How does salt perception work

Answer 7

Special Na+ sensitive channel called a ill ride sensitive sodium channels
Na+ diffuses down the conc grad
Causes depolarisation
Voltage gated Na+ and Ca2+ channels open near synaptic vesicles -> release NT

Question 8

How is acidity detected

Answer 8

Same amiloride channels allow entry of H+
If this was the only way to detect we would not be able to tell the differences
Can also block K+ selective channels K+ permeability Dec leads to depolarisation
H+ can also enter via TRP channels lead to depolarisation

Question 9

How is sweet detected

Answer 9

Proteins expressed T1R2 and T1R3
Same G protein stimulation of gustatory afferents in other tastes means that there are specific gustatory afferents for different tastes

Question 10

Bitter receptors

Answer 10

Protein T2R

Question 11

Umami receptor

Answer 11

T1R1 and T1R3

Question 12

What is the G protein mechanism after being activated by the receptor

Answer 12

PLC increasing production of IP3 and DAG
IP3 activates special type of ion channels allowing Na+ to enter causing depolarisation and then the opening of voltage gated ion channels
IP3 can also trigger Ca2+ release from intracellular storage sites which can trigger neurotransmitter release, stimulating the gustatory afferents axon

Question 13

Central taste pathway

Answer 13

Gustatory afferents -> cranial nerves -> brain stem -> thalamus VPM -> primary gustatory cortex
Route is believed to be ipsilateral

Question 14

3 cranial nerves

Answer 14

Anterior 2/3 - facial nerve VII chords tympani branch
Posterior 1/3 cranial nerve IX glossopharyngeal
Throats regions - Glottis, palate, pharynx, epiglottis - CN X vagus

Question 15

Where are smell receptors located

Answer 15

Olfactory epithelium at the top of the nasal cavity

Question 16

Are olfactory receptors neurones

Answer 16

YES they are the site of transduction

Question 17

Are olfactory receptors replaced

Answer 17

YES by basal cells every 4-8 weeks

Question 18

Pathway of odourant binding

Answer 18

Odourant binds to receptor -> G protein coupled response activates guanylyl cyclase -> intracellular cascade -> open action channels -> influx of Na+ and Ca2+ -> depolarisation -> AP threshold -> CNS

Question 19

Getting used to a smell

Answer 19

Receptor adaptation odourant still present but can no longer smell it

Question 20

Central olfactory pathways

Answer 20

Olfactory neurones -> olfactory bulb -> olfactory cortex

Medial Dorsal nucleus of the thalamus -> orbitofrontal cortex recognition
Limbic areas - association - memory