week 1 physiology of taste and smell

Question 1

how do we taste and smell?

Answer 1

chemoreceptors stimulated by binding of particular chemicals

Question 2

function of taste and smell

Answer 2

=pleasurable or objectionable sensation

• checkpoint for quality control
• influences the flow of digestive juice

Question 3

what are the organs of taste?

Answer 3

taste buds

Question 4

what are taste buds made up of?

Answer 4

sensory receptor cells and support cells arranged like slices of orange

Question 5

half life of taste receptor cells? replace by what?

Answer 5

10 days

replaced from basal cells within the taste buds

Question 6

where are taste buds present?

Answer 6

Taste buds are present mainly in the tongue, palate, epiglottis, and pharynx

Question 7

where do the majority of taste buds sit?

Answer 7

papillae (red, rough dots) in the tongue

Question 8

what are the 4 types of papillae? which have taste buds?

Answer 8

Filliform: most numerous – do not contain taste buds

Fungiform

Vallate

Foliate

Question 9

how do the taste buds work?

Answer 9

tastant binds to receptor cells and alters cells ionic channels, produces depolarising receptor potential, Receptor potential initiates action potentials in afferent nerve fibres which synapse with receptor cells

singlas and conveyed by cranial nerves via brainstem and thalamus to cortical gustatory areas

Question 10

the afferent taste fibres reach the brainstem by what 3 nerves?

Answer 10

VIIth cranial nerve (chorda tympani branch of facial nerve) - anterior two-thirds of the tongue

IXth cranial (glossopharyngeal) nerve - posterior third of the tongue

Xth caranial (vagus) nerve - areas other than tongue, including e.g. epiglottis and pharynx

Question 11

what ra the 5 primary tastes? what are they stimulated by?

Answer 11

Salty: stimulated by chemical salts especially sodium chloride (NaCl)

Sour: stimulated by acids which contain free hydrogen ions (H+)

Sweet: stimulated by configuration of glucose

Bitter: stimulated by diverse group of tastants, including e.g. alkaloids, poisonous substances and toxic plant derivatives

Umami (meaty or savory): triggered by amino acids especially glutamate

Question 12

what is Ageusia? caused by?

Answer 12

loss of taste

nerve damage; local inflammation (including e.g. glossitis, radiation, tobacco); some endocrine disorders

Question 13

what is hypogeusia? caused by?

Answer 13

reduced taste

chemo, medications

Question 14

what is dysgeusia? caused by?

Answer 14

distorted taste

glossitis; gum infections; tooth decay; reflux; upper respiratory infections; medications; neoplasms; chemotherapy; zinc deficiency

Question 15

where is the olfactory mucosa?

Answer 15

patch of mucosa in the ceiling (dorsal roof) of the nasal cavity

Question 16

what does the olfactory mucosa contain?

Answer 16

olfactory receptor cells, supporting cells and basal cells (secrete mucus)

Question 17

life span of Olfactory receptors ? replaced by what?

Answer 17

Olfactory receptors have a life span of about 2 month

Basal cells act as precursors for new olfactory receptor cells

Question 18

how to smell/route of the olfactory nerve?

Answer 18

odorants bind to the cilia

Axons of olfactory receptors collectively form afferent fibres of olfactory nerve

These pierce the cribriform plate of the ethmoid bone and enter the olfactory bulbs in the inferior surface of the brain

Olfactory bulbs (passing along olfactory tract) transmit smell information to reach temporal lobe and olfactory areas

Question 19

what is smelt during normal breathing and sniffing

Answer 19

During quiet breathing odorants only reach smell receptors by diffusion - olfactory mucosa is above the normal path of airflow

The act of Sniffing enhances smelling by drawing air currents upwards within the nasal cavity

Question 20

what properties must a substance have to be smelt?

Answer 20

(1) sufficiently volatile i.e. some of its molecules can enter the nose with inspired air
(2) sufficiently water soluble i.e. can dissolve in the mucus coating of olfactory mucosa

Question 21

what is anosmia? causes of it?

Answer 21

no smell (temporary or permentant)

viral infections; allergy; nasal polyps; head injury

Question 22

what is hyposmia? causes of it?

Answer 22

reduced smell

viral infections; allergy; nasal polyps; head injury + MAY BE early sign of Parkinson’s disease

Question 23

what is dysosmia? causes of it?

Answer 23

altered smell

differently interpreting some odours; and hallucinations of smell