physiology of smell and taste

Question 1

how does a sense of smell work?

Answer 1

chemoreceptors in the nose are stimulated by binding to particular chemicals
stimulation of these receptors induce a pleasurable or objectionable sensation

Question 2

how does taste work?

Answer 2

taste buds consist of sensory receptor cells and support cells
taste receptor cells synapse with afferent nerve fibres
taste buds are mainly present in the epiglottis, tongue (mainly papilla), palate and pharynx

Question 3

how often are taste buds replaced?

Answer 3

every 10 days from basal cells within the taste buds

Question 4

what are the 4 different types of papillae?

Answer 4

filliform- do not contain taste buds
fungiform - have tastebuds
vallate - have tastebuds
foliate - have tastebuds

Question 5

what does does the binding of taste provoking chemical to receptor cells do?

Answer 5

produces a depolarising receptor potential
this initiates action potentials in afferent nerve fibres which synapse with receptor cells

Question 6

how do afferent taste fibres reach the brainstem?

Answer 6

CN VII (chorda tympani branch)- anterior 2/3 of tongue
CN IX (glossopharyngeal)- posterior 1/3 of tongue
CN X- areas other than tongue including epiglottis and pharynx

Question 7

what are the 5 primary tastes?

Answer 7

bitter
sour
salty
sweet
umami

Question 8

what causes a bitter taste?

Answer 8

a diverse group of tastants including alkaloids, poisonous substances and toxic plant derivatives

Question 9

what causes a sour taste?

Answer 9

acids that contain free H ions

Question 10

what causes a salty taste?

Answer 10

stimulated by chemical salts especially NaCl

Question 11

what causes a sweet taste?

Answer 11

stimulated by configuration of glucose

Question 12

what causes an umami taste?

Answer 12

amino acids especially glutamate

Question 13

what does ageusia mean?

Answer 13

loss of taste function

Question 14

what does hypogeusia mean?

Answer 14

reduced taste function

Question 15

what does dysgeusia mean?

Answer 15

distortion of taste function

Question 16

which odours does CN I (olfactory) mediate?

Answer 16

common ones eg rose, chocolate and vanilla

Question 17

what does CN V (trigeminal) mediate?

Answer 17

chemical and non-chemical stimulus eg irritation, burning etc

Question 18

where is the olfactory epithelium located?

Answer 18

in the olfactory cleft on the cribiform plate, and very small parts of the superior and middle turbinate and septum
about 7cm into the nasal cavity from the nostril

Question 19

what type of epithelium is the olfactory neuroepithelium?

Answer 19

pseudostratified columnar epithelium

Question 20

what are the features of olfactory receptors?

Answer 20

specialised endings of renewable afferent neurons
a lifespan of about 2 months
axons of olfactory receptors collectively form afferent fibres of olfactory nerve

Question 21

how do olfactory receptors work?

Answer 21

1. pierce the cribiform plate and enter the olfactory bulbs synap with 2nd order neurones in the olfactory bulb
2. there is a complex transformation of chemical energy into a neural signal (glutamate and dopamine)
3. olfactory bulbs transmit smell information to the brain
4. from the olfactory bulb neurons pass along the olfactory tract to reach the temporal lobe and olfactory areas

Question 22

what are some conductive abnormalities in smell?

Answer 22

nasal polyps
rhinitis
nasal mass

Question 23

what are some sensory neural abnormalities in smell?

Answer 23

viral
head trauma
neurological conditions
brain tumours
medications