week 1 physiology of taste and smell Flashcards
how do we taste and smell?
chemoreceptors stimulated by binding of particular chemicals
function of taste and smell
=pleasurable or objectionable sensation
- checkpoint for quality control
- influences the flow of digestive juice
what are the organs of taste?
taste buds
what are taste buds made up of?
sensory receptor cells and support cells arranged like slices of orange
half life of taste receptor cells? replace by what?
10 days
replaced from basal cells within the taste buds
where are taste buds present?
Taste buds are present mainly in the tongue, palate, epiglottis, and pharynx
where do the majority of taste buds sit?
papillae (red, rough dots) in the tongue
what are the 4 types of papillae? which have taste buds?
Filliform: most numerous – do not contain taste buds
Fungiform
Vallate
Foliate
how do the taste buds work?
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
the afferent taste fibres reach the brainstem by what 3 nerves?
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
what ra the 5 primary tastes? what are they stimulated by?
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
what is Ageusia? caused by?
loss of taste
nerve damage; local inflammation (including e.g. glossitis, radiation, tobacco); some endocrine disorders
what is hypogeusia? caused by?
reduced taste
chemo, medications
what is dysgeusia? caused by?
distorted taste
glossitis; gum infections; tooth decay; reflux; upper respiratory infections; medications; neoplasms; chemotherapy; zinc deficiency
where is the olfactory mucosa?
patch of mucosa in the ceiling (dorsal roof) of the nasal cavity
what does the olfactory mucosa contain?
olfactory receptor cells, supporting cells and basal cells (secrete mucus)
life span of Olfactory receptors ? replaced by what?
Olfactory receptors have a life span of about 2 month
Basal cells act as precursors for new olfactory receptor cells
how to smell/route of the olfactory nerve?
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
what is smelt during normal breathing and sniffing
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
what properties must a substance have to be smelt?
(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
what is anosmia? causes of it?
no smell (temporary or permentant)
viral infections; allergy; nasal polyps; head injury
what is hyposmia? causes of it?
reduced smell
viral infections; allergy; nasal polyps; head injury + MAY BE early sign of Parkinson’s disease
what is dysosmia? causes of it?
altered smell
differently interpreting some odours; and hallucinations of smell
