Taste and smell Flashcards
where are taste buds found
tongue, palate, tonsillar pillars, epiglottis and proximal oesophagus
where are circumvallate papillae found
posterior of tongue in a v shape
taste buds are found on these papillae
where are fungiform papillae found
anterior surface of the tongue
where are foliate papillae found
lateral margins
where are taste buds found on the papillae
embedded on the sides of the papillae
what chemicals can be tasted by taste buds
potassium sodium chloride adenosine inosine sweet bitter glutamate H+
what causes sour taste
H+
what causes salty taste
Na and K ions
what causes sweet taste
sugar and other similar chemicals - glycols, alcohols, ketones and others
what causes bitter tastts
many chemicals including alkaloids found in toxic plants
what causes umami taste
L glutamate
how do taste buds work
contain receptors which depolarise taste cells by either an ionotropic or metabotropic pathway
what are the relative taste thresholds for various tastes
bitter has the lowest threshold as it most commonly associated with dangerous substances so sensitivity must be high
sour is next lowest
then sweet and then salty
what is the taste pathway to the cortex
solitary nucleus, then thalamus, then insula and anterior operculum
where do the limbic components of taste go
via the thalamus
can activate brainstem nuclei for salivation or vomiting
where does pain from spicy food travel
posterior parts of tongue to cn 5
what are the components of the olfactory system
olfactory epithelium
receptor cells (bipolar neurons)
axons that project to the olfactory bulb
neuronal tract to multiple olfactory destinations in the brain
where is the olfactory epithelium
high in the nasal cavity below the cribriform plate
what types of neurones detect smell
bipolar
where is the olfactory bulb
just above and anterior to the cribriform plate
what gland secretes mucus into the olfactory epithelium
bowman’s gland
what strucuture detects odorants
olfactory cillia formed from the olfactory knob
describe activation of the odorant receptor
an molecule binds to the receptor of the primary olfactory neurone
the activated receptor activates a G protein which stimulates adenylyl cyclase to convert ATP to cAMP
cAMP activates a cation channel, making it permeable to Na +and Ca2+, thus depolarising the cell
what is the frequency of action potentials proportional to
log concentration of odorant
how many genes are there for odorant receptors
over 300
each neuron expresses just one gene per neuron
what are the 7 types of odour
- Camphoraceous
- Musky
- Floral
- Pepperminty
- Ethereal
- Pungent
- Putrid
what is the function of the medial olfactory pathway
feeds into limbic system and encodes the emotional aspect olfaction and memory (ancient part)
what is the function of the lateral olfactory pathway
feeds to less ancient parts of brain such as the pyriform cortex in the temporal lobe
involved in likes and dislikes as well as visceral reactions via brainstem, does not go via the thalamus
what is the more recent olfactory pathway
thalamus
to orbitofrontal cortex
involved in conscious discernment of odour
where does the olfactory tract project to
olfactory cortex
hypothalamus, amygdala, limbic system, hippocampus
what reflexes can olfaction cause
salivation, gastric secretions, sneezing
gagging, vomiting
