Lecture 7 Flashcards
Both of these are required to taste flavor
olfaction and taste
airborne molecules that bind to receptors in the nose
odorants
What are the functions of the olfactory system?
– detects odorants
– provides info about food, self, others, animals, plants, etc.
– influences feeding behaviors, social interactions, reproduction
– processes information about identity, concentration, and quality of wide range of chemical stimuli
receptors in the nose that project to neurons in the ipsilateral
olfactory bulb
olfactory epithelium
bundled axons that project to primary olfactory cortex
olfactory tract
What is unique about the olfactory senses?
– no thalamic relay between primary receptors and cerebral cortex
– ipsilateral projections
When do olfactory signals reach the thalamus?
During higher level processing; reactions to olfactory stimuli; also location of crossing
___ is located at the top of the nasal cavity. Odorants are carried along mucosa and come in contact with ___. Receptors located in the ___.
olfactory mucosa
sensory neurons
cilia
Humans have ___ types
of receptors. Each olfactory neuron expresses a ___ olfactory receptor. Each receptor can bind to ___ odorants. Each neuron that expresses a given receptor targets the same ___ in the olfactory bulb.
350
single
multiple
glomeruli
In dogs vs humans, receptors are ___ sensitive but the __ of receptors varies greatly.
equally
number
When an odorant binds to receptor, it activates __ that in turn activates __.
This generates __, which opens a ___. __ rushes in, and opens a __ channel. This ion leaves down its concentration gradient and leads to __.
G-protein (Golf) adenylyl cyclase III cAMP Na+/Ca2+ cation channel calcium chloride depolarization
Describe what happens during adaptation/fatigue.
- calmodulin binds up Ca2+
- cAMP is broken down by phosphodiesterases
- Ca2+ is pumped out of the cell
- Ca2+-CAM binds to Cl- channel, which closes the channel
- initially notice smell, gradually desensitized
Describe the specificity of olfactory receptors.
- some neurons selectively respond to a single odorant
- others respond to multiple
- some odorants can activate multiple receptors
- specific receptors may be part of the code for multiple odorants
- differences likely stem in genetics
Unlike other sensory receptors (e.g., photoreceptors), olfactory receptors have axons that project ___. Axons form bundles as they leave the olfactory epithelium, known as the ___, which projects ipsilaterally to olfactory bulb.
directly to the brain
olfactory nerve
ipsilaterally
located above the nasal passages; where sensory information is collected and sorted
olfactory bulb
Why is olfaction generally considered the least acute sense in humans?
– # of olfactory
receptors (small)
– size of olfactory bulb (very small)
Olfactory receptor neurons project to the ____, a spherical structure where receptor axon terminal synapses onto ___, which project to the cerebral cortex. This is an __, ___ synapse. Lateral inhibition is done by ___ and ___.
glomeruli mitral cell dendrites excitatory glutamatergic periglomerular cells granule cells
Olfactory receptors localized into ___, with a different set of odorant receptors expressed in each ___. Olfactory receptor neurons that express a particular odorant receptor converge on ___. Individual glomeruli respond selectively to ____.
discrete areas
zone
a specific glomeruli
specific odorants
____ is preserved in the olfactory bulb. Olfactory mucosa divided into __ zones. Each zone contains ___ receptors. Specific receptor types are only found in ___. Odorants tend to activate receptors within ____.
sectoring 4 a variety of one zone a particular zone
The olfactory bulb connects to the ____, also known as the primary olfactory cortex, located in the ____. It is unique because it ___.
piriform cortex
temporal lobe
only has 3 layers
The primary olfactory cortex connects to the ___, known as the ___ cortex, located in frontal lobe.
secondary olfactory cortex
orbitofrontal cortex
frontal lobe
The piriform cortex also projects to ___, ___, etc. Information can cross at the ____.
thalamus
amygdala
anterior commissure
inability to identify common odors; often restricted to a single odorant; congenital or acquired
ansomia
There are two neurogenic hotspots in the adult, located along the length of the ___ near the margin of the ____. New neurons are added in the ___ and the ____.
neuraxis
ventricles
olfactory bulb
dentate gyrus of the hippocampus
New neurons in the olfactory bulb originate as stem cells in the ____ of the ____.
subventricular zone (SVZ) lateral ventricle
Cells in the SVZ give rise to most neurons in the forebrain during development. It goes from ____ to ___ to ___. Neurogenesis persists ___.
SVZ astrocyte
transit amplifying cell
neuroblast
throughout life
When generating new olfactory neurons, neuroblasts migrate in the ___ in __ days. A chemical in olfactory bulb ___ migrating cells, and a different chemical near SVZ ___ migrating cells. Once in the olfactory bulbs, neuroblasts ___ (___ days). Finally, they integrate into the ____ (___ days) and respond to olfactory stimuli.
RMS (rostral migratory stream) 2-6 attracts repels differentiate 15-30 already existing network 15-30
SVZ-derived cells differentiate into two types of interneurons (inhibitory). Name them and their percentage of occurrence.
periglomerular cells(~25%) granule cells (~75%)
Within __ weeks after generation, cells can fire action potentials and make synapses, although there is no ___.
2 net growth (i.e., neurons must also die)
What is the maintenance hypothesis?
At any given moment, new neurons are frozen and ready. If they are not needed, they die. If they are needed, they complete differentiation, migrate to final destination, and establish synaptic connection (proposed a role in odor learning).
It is possible to regenerate olfactory receptors. There is persistent neurogenesis among __, which differentiate, develop into ___, grow ___ that project back to the ___ to re-establish connections.
basal cells
sensory neurons
axon processes
olfactory bulb
intranasally infused to cause damage to the olfactory epithelium
in experiments
ZnSO4
specialized structure that recognizes species-specific odorants called pheromones; plays important roles in social, reproductive, and parenting behavior
vomeronasal organ (VNO)
VNO projects to accessory __, which in turn projects to ___.
olfactory bulb
hypothalamus
Do humans detect pheromones?
no
What would lesioning the VNO in animals result in?
compromised sexual selection and dominance hierarchies
What are the roles of gustation?
- used to determine whether food should be ingested (together with smell, touch, pain)
- provides info about identity, concentration, and pleasant/unpleasant quality
- helps get GI system ready to receive food (i.e., saliva and swallowing) or reject food (i.e., regurgitation)
The tongue contains both ___ and ___. However, it does NOT process information about ___ and ___ of things in your mouth, that is done by somatosensory receptors.
peripheral receptors
central processing
temperature
texture
What are the 5 basic tastes and what do they measure?
- sweet (sugars and starches - sucrose, aspartame, glycine, etc.)
- salty (Na+, K+, and others)
- sour (acids - H+ - avoid)
- bitter (bases and toxins - avoid)
- umami (savory, glutamate, MSG)
Taste receptors are organized in ___ (~10K).
These contain 30-100 ____. 75% of all taste buds packed together in ____.
taste buds
taste cells
papillae
What are the 3 types of papillae and where are they located on the tongue?
– fungiform (anterior tongue)
– circumvallate (largest, rear of tongue)
– foliate (posterolateral edge)
Single taste bud organized so that receptors are ___ and the synapse ____. Taste receptors ___ the neurons in number. Taste receptor cells form synapses on ___, which project to ___ and then to the brain.
apical basolateral equal gustatory fibers gustatory ganglia
Chemosensory transduction occurs at the ___ end while graded potentials at ___ end generate electrical signals.
apical
basal
Salty and sour rely on movement of ___ through channels, which flow down concentration gradient, __ the membrane. ___ channels open and lead to further membrane depolarization.
____ channels open and allow NT release onto ___ that project to the brain. This generates action potentials in those neurons.
ions (Na+ or H+) depolarizing voltage-gated Na+ voltage-gated Ca2+ gustatory fibers
Sweet, umami, and bitter taste uses ___ for signal transduction.
GPCRs
There are wo groups of gustatory GPCRs: __ (3 types) and __ (~40 types). Both expressed specifically in ___ and both related to ___.
Individual taste cell can express one or the other, or neither, but not both.
T1R
T2R
taste cells
odorant receptors
___ is a cycloheximide receptor (bitter).
T2R5
What are the receptors for sweet and umami?
sweet: T1R3 + T1R2
umami: T1R3 + T1R1
*T1R1 and T1R2 are expressed in non- overlapping taste receptors
How does signal transduction work in the sweet and umami receptors?
-receptor activation leads to activation of PLC, which increases IP3 and opens Ca2+-dependent channels (TRPM5 – Na+ cations)
-cell is depolarized
-voltage- gated Ca2+
channels open
-NT release
The bitter taste receptor is a GPCR called ___, which has __ subtypes. It uses a specific G-protein called ___ (unique to bitter) It follows the same pathway as the sweet and umami pathways.
T2R
40
gusducin
Carbonation is a “new” taste; some sour taste cells have an enzyme called ____ on their surface that catalyzes reaction ___. ___ activate sour receptor.
carbonic anhydrase
HCO3 –> CO2 + H+
protons (H+)
sour + fizz
carbonation
The receptors that detects sour taste is ____.
PKD2L1
What is the role of the regulatory region (promoter) of an expression vector?
directs where and when a gene is expressed
What is the role of a protein coding region in an expression vector?
provides the code for the transcribed to mRNA, translated to protein
Why are cats insensitive to sweet tastes?
lack 247 bp of the gene that encodes for the T1R2 receptor –> cannot make functional receptors
Why do pandas love artificial sweeteners?
unique structure of T1R2 receptor (but they lack T1R1 receptor –> no umami)
What is unique about the sweet receptors in birds?
birds also lack T1R2 receptors
• hummingbirds feed on nectar (sweet)
• T1R1-T1R3 receptor took over…. residues in T1R3 have mutated –> no longer sense umami, now sweet
Bitter receptor in bitter cells leads to increasing ___.
However, bitter receptor in sweet cells leads to increasing ___. This means ____.
aversion
attraction
it’s the cell not the chemical that has meaning
What are miracle berries?
They are tasteless at neutral pH; convert sour stimuli to strong sweetness. At low pH (i.e., sour), miraculin binds to T1R2 receptor and distorts it – only activates sweet receptor in sour environment; possibly blocks sour receptor as well
Supertasters are specifically more sensitive to ___ compounds.
bitter
Information from taste receptors remains __ in the brain.
segregated
Taste cells synapse with ___
and enter the brain through ___, which each innervate different part of tongue. These project to the ___ (solitary tract) and then to ____.
This projects to to various cortical areas, including ____ in parietal lobe, ___ and ___.
primary sensory neurons 3 cranial nerves (VII, IX, X) medulla ventral posterior medial nucleus of thalamus (VPM) primary gustatory cortex amygdala hypothalamus
combination of smell, taste, and other sensations
flavor
The ___ receives input from multiple sensory modalities; it is the first place where taste and smell signals meet. The firing of these neurons also affected by ___.
orbitofrontal cortex
hunger level
