Physiology of Taste and Smell Flashcards
What type of receptors are responsible for taste and smell?
chemoreceptors
Taste perception can be influenced by smell receptors. TRUE/FALSE?
TRUE
What are the two main types of cell found in the taste buds?
sensory receptor cells
and support cells
What cells regenerate the receptor cells, and after how long?
replaced from basal cells
after about 10 days (lifespan)
What type of nerve fibres are present behind the taste buds to rely information to the brain?
afferent nerve fibres
Where are taste buds mainly present?
tongue
palate
epiglottis
pharynx
Where are taste buds found in the tongue?
In papillae
What are the four types of papillae found on the tongue?
Filliform
Fungiform
Vallate
Foliate
What type of papillae do NOT contain taste buds?
Filliform
mostly found at tip of tongue - are sensitive to touch and temp
How do APs arise in the afferent nerve fibres behind the taste buds?
Tastants bind to receptor cells
Depolarise membrane
Fire AP
Where are taste signals processed in the brain?
cortical gustatory areas
What cranial nerves are involved in afferent signals of taste reaching the brainstem?
CN VII - chorda tympani = anterior 2/3 of the tongue
CN IX = posterior 1/3 of the tongue
CN X = areas other than tongue, e.g. epiglottis and pharynx
What are the 5 primary tastes?
Salty Sour Sweet Bitter Umami (meaty or savory)
What chemical compound provokes a salty taste?
NaCl
What chemical provokes a sweet taste?
Glucose or a configuration of glucose
What ion is responsible for sour tasting food?
H+
What substances cause a bitter taste in the mouth?
diverse group of tastants:
- alkaloids
- poisonous substances
- toxic plant derivatives
Umami taste is provoked by what chemical compound?
amino acids especially glutamate
What is the difference between Ageusia, Hypogeusia and Dysgeusia?
Ageusia (loss of taste function)
Hypogeusia (reduced taste function)
Dysgeusia (distortion of taste function
What can cause ageusia?
- nerve damage
- local inflammation (e.g. glossitis, radiation, tobacco)
- some endocrine disorders
What can cause hypogeusia?
chemotherapy
medications
What can cause dysgeusia?
glossitis gum infections/tooth decay reflux URTI medications/chemotherapy neoplasms zinc deficiency
What are the 3 cell types found in the olfactory mucosa?
olfactory receptor cells
supporting cells
basal cells
What are olfactory receptors?
specialised endings of renewable afferent neurons
How do the neurons of olfactory receptors appear?
thick short dendrite and an expanded end called an olfactory rod
What part of the olfactory nerve pierces the cribriform plate of the ethmoid bone to enter the olfactory bulbs in the brain?
Axons of olfactory receptors collectively form afferent fibres of olfactory nerve which pierce the ethmoid bone
After reaching the olfactory bulb, where are signals transmitted to perceive a smell?
neurons passes along the olfactory tract to reach temporal lobe and olfactory areas
Why is quiet breathing less efficient for perceiving smells?
olfactory mucosa is above the normal path of airflow
=> During quiet breathing odorants only reach smell receptors by diffusion
What are the 2 factors which enhance the ability to smell a substance?
Substance is sufficiently volatile
It is sufficiently water soluble
=> i.e. can dissolve in the mucus coating of olfactory mucosa
WHat is the difference between anosmia, hyposmia and dysosmia?
Anosmia (inability to smell):
Hyposmia (reduced ability to smell):
Dysosmia (altered sense of smell)
WHat causes anosmia and hyposmia?
viral infections
allergy
nasal polyps
head injury
Hyposmia may be early sign of Parkinson’s disease
What is caused in dysosmia?
differently interpreting some odours
hallucinations of smell
