physiology-smell and taste Flashcards
how are chemoreceptors stimulated?
by binding to certain chemicals
what allows taste and smell?
- taste receptors
- chemoreceptors
how are the sensory receptors in the taste bus organised?
packaged close together
what do taste buds consist of?
sensory receptor cells and support cells arranged like orange slices
how long is the life span of a taste receptor cell nd how are they replaced?
about 10 days
-replaced from the basal cells within the taste buds
what do taste receptor cells synapse with?
afferent nerve fibres
where do taste buds present?
-mainly in tongue, palate, epiglottis and pharynx
where on the tongue do most taste buds sit?
on papillae
what are papillae?
- finger like structures which give rise to the rough appearance of the dorsum of the tongue
- can be seen on the tongue as little red dots or raised bumps
what are the 4 types of papillae seen on the human tongue?
- filliform (most numerous and only one to not contain taste buds)
- fungiform
- vallate
- foliate
what is the most numerous type of papillae?
filliform
which papillae contain taste buds?
- fungiform
- vallate
- foliate
which papillae does not contain taste buds?
filliform
how do you taste?
- binding of taste provoking chemical (tastant) to receptor cells produces depolarising receptor potential
- receptor potential intiates action potentials in afferent nerve fibres which synapse with receptor cells
- signals conveyed by cranial nerves via brainstem and thalamus to cortical gustatory areas
how do afferent taste fibres reach the brainstem?
via:
CNVII (chorda tympany branch of facial nerve) for anterior 2/3 of tongue
CNIX (glossopharyngeal nerve) for posterior 1/3 of tongue
CNX (vagus) for areas other than tongue e.g. epiglottis and pharynx
what stimulates bitter tastes?
diverse group of tastants e.g. alkaloids, poisonous substance and toxic plant derivatives
what stimulates sour tastes?
acids which contain free hydrogen ions (h+)
what stimulates salty tastes?
chemical salts especially sodium chloride (NaCl)
what stimulates sweet tastes?
the configuration of glucose
what stimulates unami (meaty or savory) tastes?
amino acids especially glutamate
what is ageusia?
loss of taste function
what can cause ageusia?
- nerve damage
- local inflammation
- some endocrine disorders
what is hypogeusia?
reduced taste function
what can cause hypogeusia?
chemotherapy or radiotherapy
what is dysgeusia?
distortion of taste function
what may cause dysgeusia?
- glossitis
- gum infections
- tooth decay
- reflux
- URI
- meds
- neoplasms
- chemo
- zinc edficiency
what are the 4 neural systems within the left and right sides of the nose?
- main olfactory system (cranial nerve I)
- trigeminal somatosensory system (cranial nerve V)
- the accessory olfactory system
- the nerve terminalis
what neural system mediates the common odours (rose, vanilla, chocolate)?
olfactory nerve (CNI)
what neural system mediates chemical and non chemical stimulus and why is it important?
CNV (trigeminal nerve)
- can detect irritation, burning, cooling ect
- can make you cough in response
what is important in the production of flavour from swallowed foods adding smell to taste and touch?
olfactory epithelium which exists in a small region of nasal epithelium
what is needed for a substance to be smelled?
- sufficiently volatile (enter nose in aerosol form)
- sufficiently water soluble to dissolve in mucus coating of olfactory mucosa
what must the odourant do before neural conduction can occur from the olfactory cleft to the brain?
- enter nose during active (sniffing) or passive (diffusion) process
- pass to the olfactory cleft
- move from the air phase to the aqueous phase
why is mucus important in smell?
- moist and protective environment
- aids in dispersing odourants to the olfactory receptors
- from the mucus odourants either diffuse or are transported by specialised proteins to the receptors
describe the olfactory neuroepithelium
pseudostratified columnar epithelium
what cells does the olfactory neuroepithelium contain?
- bi polar sensory neurone (CNS in origin) extends odourant receptor containing cilia into the mucus
- supporting cells (insulates and protects)
- duct cell of bowmans glands secretes mucus
- basal cells (stem cells)
what is phantosmia?
smell perceived in the absence of stimulus
