Flashcards in Chemical Senses Deck (41):
What do small positively charged things taste like?
What 4 things encode taste or are important to taste?
Pattern of neural activation
Other perceptual elements like temperature
What are the two chemical senses and what type of receptors do they have?
gustation and olfaction have chemoreceptors
Give the hierarchy of structures in taste (ie different cell/structure types)
What are the components of a taste bud?
Microvilii project into the taste pore and then an orange like array of taste cells surrounds. Basal cells are at the end of the taste bud and provide support
Where are the four basic tastes tastable?
All over the tongue.
How can you only stimulate certain parts of the tongue with a taste?
By using very very low concentrations of it
Describe the papillae
Bathed in fluid, the papillae are covered in taste buds (hundreds per papillae, 2000-5000 a person). Each papillae has a taste that it is maximally sensitive to
How many taste buds are in people (n practice)
Range from 500 to 20000, though most say 2000-5000
How long does it take for taste cells to turnover?
Every two weeks
What are axons from taste cells called?
Gustatory afferent axons
Are taste cells capable of having action potentials? What type of potentials do they have?
They can produce action potentials after building up a large enough receptor potential
How many tastes can a taste cell detect?
Taste cells can detect 1 or more tastes, though usually more than one.
What are the sodium channels of salty taste receptor cells like?
They are not voltage gated and they are always open at rest. Depolarization from sodium influx causes calcium to enter the cell and cause neurotransmitter release in an action potential
What are sour taste cell receptor channels like? How do sour tastes give a double whammy depolarization?
Same as the salty sodium ones, except they let protons and high energy anions in. Protons can block potassium channels, preventing it form leaving the cell and causing an even greater depolarization
What three tastes use a G protein coupled receptor? What is the effector protein in these pathways called?
Sweet, bitter and umami have G protein coupled receptors.
The effector protein for these G proteins is called phospholipase C
What does phospholipase C do in gustation?
When it is activated by the G protein it makes IP3 which causes inflow of calcium from calcium stores/extracellular and inflow of extracellular sodium
Why can't bitter flavours be distinguished even though there are 30 different types of T2R receptors?
All 30 types exist on one taste cell, which sends one ambiguous action potential regardless of which receptor is activated
What two types of receptor proteins do sweet tastes activate?
T1R2 and T1R3
What type of receptors do umami tastes activate? (two)
T1R1 and T1R3
How many cranial nerves innervate the tongue? Which ones?
Facial nerve (front of tongue)
Laryngeal nerve (back of tongue)
Vagus nerve (Down to pharynx)
Where do the three cranial nerves of the tongue innvervate>
All converge onto gustatory nucleus in brainstem
Where do axons from the gustatory nucleus on the brainstem go? Where do they go from there?
To the thalamus, on the ventral posterior medial (VPM) nucleus, this part of the thalamus deals with sensory info from the head. From there the VPM taste neurons send axons to the primary gustatory cortex
Where is the primary gustatory cortex located?
On Brodmann's area 36 and the insula-operculum regions of the cortex, near the tactile representation of the tongue
Which two pathways flow out of taste system?
1 goes down into ventral brainstem for swallowing, vomiting and salivating
One is involved in conscous mediation of perception of taste
Is there decussation in taste pathways?
What gives the vast variety of tastes available to us?
The relative activation of tase cells
Where is the olfactory epithelium?
On the roof of the nasal cavity
What is the bone that seperates the oflactory epithelium from the olfactory bulb?
The cribiform plate
What three things are in the mucus layer of the olfactory epithelium?
Salts, sugars, enzymes and antibodies
The enzymes are to stop stimulation once odour has arrived
Why are dogs more sensitive to smell?
Greater number of olfactory receptor cells
What type of receptor is there on the olfactory receptor cell?
A G protein coupled receptor with the effector adenylyl cyclase (makes cAMP to open calcium channels)
What happens when a receptor is activated on a olfactory receptor cell?
The G protein is activated which then activates adnylyl cyclase. Adenylyl cyclase makes cAMP, which opens calcium channels. Inflow of calcium causes opening of chloride channels (to let it out). Letting chlorine out of the cell depolarizes it,
What part of the olfactory receptor cells do odours interact with?
The cilia on these cells
Are olfactory receptor cells exclusive to one smell?
No,they are selective but not exclusive to one smell.
What are the repeating units of the olfactory bulb?
The glomerulus, which connects olfactory receptor cells to second-order olfactory neurons.
What type of inputs do glomerulus have?
Similar types of cells from across olfactory epithelium going to same glomerulus results in a segregation of info.
What are the two pathways out of the olfactory bulb?
I goes to olfactory tubercle, which then relays axons to medial dorsal nucleus (in thalamus) to orbitofrontal cortex (conscious detection of odours)
The second goes to the olfactory cortex and temporal lobe. First goes to olfactory cortex without synapsing in the thalamus, and then the pitiform cortex under the brain (medial), which has a direct connectivity with olfactory and limbic system.
What causes the change in colour in colour sensitive dye?
The polarity of fluid molecules.
What makes each olfactory receptor cell different?
Each one has its own type of receptor cell protein, there can be repeats of these cells scattered through the epithelium, these respond to different odours differently