The Chemical Senses(Olfaction and Gustation)

Topic 8

what are papillae?

protrusions on the tongue that help to grip food

what are the kinds of papillae?

vallate, fungiform, and foliate

what are taste buds?

clusters of taste receptor cells

what is a receptor potential?

tastant binding causes depolarization of cell

what is transduction?

environmental stimuli evoke an electrical response in a sensory receptor

what does a sensory receptor do?

receptor potential triggers neurotransmitter release, gustatory afferent axons are stimulated

how do taste stimuli(tastants) function?

pass directly through ion channels, bind and block ion channels(sour), bind to G-protein-coupled receptors and activate second messenger to open ion channels (bit

what is the basic taste pathway?

taste cells synapse onto gustatory afferent axons

what are gustatory afferent axons?

project to gustatory nucleus via cranial nerves (VII, IX, and X)

what does the ventral posterior medial nucleus (VPN) do?

receives input from gustatory nucleus, project to primary gustatory cortex(Bordmann’s area 36)

where is the VPN located?

in the thalamus

what are localized lesions?

result in the loss of taste perception

what is ageusia?

inability to taste

what is the labelled line hypothesis?

individual taste receptors represent each kind of taste

what is population coding?

large numbers of broadly tuned neurons, temp and textual features of food play a role

what is a pheromone?

a smell that provides a communication

what is an odorant?

activate transduction process in olfactory cells

what is the olfactory nerve?

olfactory receptor cell axons

what is the cribriform plate?

thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb

what is anosmia?

the inability to smell, can come from a head trauma which damages olfactory axons

what are the steps for olfactory transduction?

odorant molecules binds to receptor, G-protein activated, activation of adenyl cyclase→formation of cAMP(ATP is converted into cAMP), cAMP binds to cAMP-gated cation channel, influx of Ca2+ and Na+, opens Ca2+ activated Cl- channel→Cl- ions leave the cell as a result of Ca2+, current flow and membrane depolarization

why does Cl- produce depolarzation?

Cl- ions are negative so more positive charge is inside the cell

what do olfactory receptor cells do during stimulation?

generate receptor potentials and action potentials

what does a glomerulus do?

receives input from one type of olfactory receptor cell

what are the axons of the olfactory tract?

branch and enter the forebrain

what is the orbitofrontal cortex (part of the neocortex)?

reached by a pathway that synapses in the medial dorsal nucleus of thalamus