Physiology of Taste and Smell Flashcards
how do taste and smell influence foot intake
induces a pleasurable or objectionable sensation
checkpoint for quality control
influences flow of digestive juices
what are the organs of taste
taste buds (contain sensory receptor cells)
what makes up taste buds
sensory receptor cells and support cells
what is the lifecycle of taste receptor cells
last about ten days
are replaced from basal cells within the taste buds
where are taste buds
tongue, palate, epiglottis and pharynx
majority in the papillae in the tongue
what do taste receptor cells synapse with
afferent nerve fibres
what are papillae
finger like structures, give rough appearance to the dorsum of the tongue
what are the four types of papillae- which ones contain taste buds
filliform (most numerous do not contain taste buds) fungiform vallate foliate (last three all contain taste buds)
describe how taste produces responses in the brain
tastant (taste provking chemicals) bind to receptor cells altering the cells ionic channels- produces depolarising receptor potential
receptor potential initiates action potential in afferent nerve fibres which synapse with receptor cells
signals conveyed by cranial nerves (CNII, IX, X) via brainstem and thalamus to the cortical gustatory areas
in taste what is the role of CN VII
chorda tympani branch supplies the anterior 2/3rd of the tongue
in taste what is the role of CN IX
supplies the posterior 1/3rd of the tongue
in taste what is the role of CN X
supples areas other than the tongue (epiglottis, pharynx)
what are the five primary tastes
salty, sour, sweet, bitter, umami (meaty or savory)
what stimulates salty tastes
chemical salts -esp sodium chloride
what stimulates sour tastes
acids which contain free hydrogen ions
what stimulates sweet tastes
configuration of glucose
what stimulates bitter tastes
diverse tastants- inc: alkaloids, poisonous substances, toxic plant derivatives
what stimulates umami tastes
triggered by amino acids (esp glutamate)
what is ageusia
loss of taste function (can be temporary or permanent)
what can cause ageusia
nerve damage, local inflammation (glossitis, radiation, tobacco), endocrine disorders
what is hypogeusia
reduced taste function
what can cause hypogeusia
chemotherapy, medications
what is dysgeusia
distortion of taste function
what can cause dysgeusia
many causes inc:
glossitis, gum infections, tooth decay, reflux, URTI, medications, neoplasms, chemotherapy, zinc deficiency
where is the olfactory mucosa
in the ceiling of the nasal cavity (dorsal roof)
what are the three types of cells in the olfactory mucosa
olfactory receptor cells, supporting cells, basal cells (secrete mucous)
what are olfactory receptors
specialised endings of renewable afferent neurones
each has thick short dendrite and an expanded end called an olfactory rod
what do the olfactory rods do
cilia project from these
what are odorants
molecules that bond to the cilia on the olfactory rods
what is the life cycle of olfactory receptors
lifespan of 2 months
basal cells act as precursors for new olfactory receptor cells
describe the formation and path of the olfactory nerve to the brain
axons of the olfactory receptors collectively form the afferent fibres of the olfactory nerve
these pierce the cribriform plate of the ethmoid bone and enter the olfactory bulbs in the inferior surface of the brain
from the bulbs neurones pass along the olfactory tract to reach the temporal lobes and olfactory areas
can you smell during quiet breathing
odorants only reach smell receptors by diffusion (olfactory mucosa is above the normal path of airflow)
why does sniffing enhance smelling
draws air currents upwards towards the olfactory mucosa
what must a substance be in order to be smelt
sufficiently volatile (molecules can enter nose with inspired air) sufficiently water soluble (can dissolve in the mucous coating the olfactory mucosa
what is anosmia
inability to smell (can be temporary or permanent)
what can cause anosmia
viral infections, allergy, nasal polyps, head injury
what is hyposmia
reduced ability to smell
what can cause hyposmia
similar causes to anosmia
can also be early sign of parkinsons
what is dysosmia
altered sense of smell (interpreting some odours and hallucinations of smell)
