Ch. 54 - chemical senses taste and smell Flashcards
Why do chemical senses bring up emotions
pass through limbic system
Benefits of chemical senses (4)
- separate undesirable/ lethal foods
- initiate physiological response for digestion and utilization of food (i.e. salivating)
- recognize proximity to other aimals/individuals
- emotional and behavioral functions
____% of taste is smell
50-70%
What do the chemical receptors in taste cells sense
ions, compounds
Sour taste buds recept
acids (hydrogen ion concentration)
Salty taste buds recept
Na+
Sweet taste buds recept
organic chemicals
(don’t recept a single class of chemicals)
Bitter taste buds recept
organic substances, often nitrogen, alkaloids
(often toxic)
Alkaloid bud receptors recept
quinine, caffeine, nicotine, plant toxins
umami bud receptors recept
L-glutamate
i.e. meat, cheese
What has the lowest threshold for taste
bitter (much more sensitive than all others)
Taste blindness is usually with
thiorea compounds
Taste bud make up:
50 epithelial cells
Contain: sustentacular cells and taste cells
Taste cell turnover
fast - continually going through mitosis
How do taste cells work
microvilli/taste hairs protrude outward with receptor surface for taste
Taste nerve location
wraps around bodes of taste cells
Three types of papillae:
- fungiform
- foliate
- palate and tonsillar pillar
Most abundant papillae
fungiform - more important for texture
Amount of taste buds (age)
kids>adults>geriatric
Each taste but responds to ____ taste sitmuli
one (of five)
What causes change in membrane potential with taste receptor?
taste chemical–>taste hair –> partial loss of negative potential (graded APs)
cell becomes more positive inside w/ stimulation
decrease in potential is proportional to
concentration of stimulating substance
Taste AP pathway
chemical binds to protein receptor molecule on outer surface –>positie ions enter and depolarize cell
What washes away taste stimulus?
Saliva (repolarizes)
What tastes are ion specific?
Salty and sour
salty = Na+
Sour = H+
What tastes are second-messenger transmitter substances?
Sweet and bitter
Taste adaptation
quick - first application is when discharge reaches peak. After, quickly adapts
Two transmission of taste signal:
- anteroro 2/3 tongue –>lingual nerve –>chorda tympani –>facial nerve –>tractus solitarius
- Circumvallate papillae –>glossopharyngeal–>tractus solitarius
Taste fiber (both) pathway:
synapse in nuclei of tractus solitarius –>2nd order neurons to ventral posterior medial nucleus of thalmus –>thirr order neurons to lower tip of postcentral gyrus in parietal cerebral cortex
Taste reflexes
tractus solitarius –>superior and inferior salivatory nuclei
Control secretion of saliva during ingestion/digestion
Adaptation of taste signals (2 areas)
- slight/partial at taste buds
- complete adaptation in CNS (cerebral cortex)
adaptation of taste signals occurs within
one minute
Taste preference is based on
physiologic need (i.e. need salt crave salt)
taste preference MOA is from
CNS
What sense is the least well understood?
smell
Olfactory membrane location
superior part of nostril, superior septum, superior/middle turbinate
How is smell sensed?
Hairs/cilia project into mucous–>bind chemical odorants
What are the only cells that are externally exposed?
Hairs/Cilia of olafactory
What makes mucous?
Bowman’s gland
Stimulation of olfactory senses
2nd messanger mechanims
Pathway for stimulation of olfactory senses
odorant to mucous–>binds to receptor proteins in cilia membrane–>transmembrane protein
2nd messanger pathway
transmembrane coupled G-protein–>alpha subunit –>adenylyl cyclase –>activates cyclase–>cyclase converts ATP to cAMP–>activates gated sodium ion channel
2nd messenger system benefit
multiplies excitatory effect of weak odorants (amplifies)
resting olfactory membrane potential
-55 mV
odorants depolarize to
-30 mV
Olafactory receptor adaptation
50% in first second after stimulation
Smell sensation classifications (7)
- camphoraceous
- musky
- floral
- pepperminty
- ethereal
- pungent
- putrid
Smell range
Small gradation in intensity but can be detected at very small concentrations (low thresshold to smell a smell)
Olfactory bulb nerve fibers go to
cranial nerve I or olefactory tract
olfactory cells have ___ and terminiate in
short axons and terminate in gomeruli of olfactory bulb
glomeruli reponse
different glomeruli respond to different odors
3 different pathways in CNS
- very old
- less old
- newer
Very old olafacotry system location
nuclei inmidbasal portion of brain anterior to hypothalmus. Feeds into limbic system
very old olfactory system role
activating feeding systems (salivation and digestion)
less old olafactory system location
prepyrform and pyrifom cortex and amygdaloid nuclei, pass through all portions of limbic system
less old olafactory system role
like or dislike certain foods
newer olfactory pathway location
thalmus *only one that does
newer olfactory pathway role
concious analysis, higher order thinking
emotions, memories, complex thoughts