The Chemical Senses - Olfactory and Taste Flashcards
What information does the olfactory system process?
identity, concentration, and odorants
What are odorants?
quality of airborne, volatile chemical stimuli
Odorants interact with what? Where?
olfactory receptor neurons (ORN) found in the olfactory epithelium
What do the olfactory receptors contain in their membranes?
specialized GPCRs odorant receptors
There are nearly _____ odorant receptor genes.
1,000
Each olfactory receptor neuron expresses how many odorant receptor genes?
only one or a few
Respiratory epithelium depends on what?
air temp and moisture-immune barrier
Function of mucus.
protect and control ionic milieu
What are the 4 characteristics of ORNs?
1) small diameter
2) unmyelinated
3) bipolar cells with a single dendritic process
4) several microvilli (olfactory cilia)
basal cells are located where?
bottom of cell
where are sustentacular cells?
top of cell
What is the function of sustentacular cells and basal cells?
offer support and protection by secreting enzymes that break down chemicals
What is considered harmful exposure in relation to regeneration?
olfactory unsheathing cells
The human olfactory system is capable of making distinctions based on what?
small changes in molecular structure and based on concentration
The only classification of odors is what (2)?
1) either pleasant and attractive
2) unpleasant and repulsive
Receptor potentials are generated where?
in the cilia of receptor neurons
What evokes a large inward (depolarizing) current only when applied to the cilia?
odorants
Calcium mechanism channels are _______-dependent.
calmodulin
What does Kinase II restore and reduce?
restore G(olf) and reduce cAMP
What two things are involved with Kinase II?
1) phosphodiesterase
2) beta-arrestin
Function of beta-arrestin?
modify receptor sensitivity
Axons arising from receptor cells project through what directly to neurons in the what?
the cribiform plate directly to neurons in the olfactory bulb
In what type of arrangements do olfactory receptor axons terminate?
in specialized synaptic arrangements (glomeruli) on dendrites of mitral cells
What are mitral cells?
projection neurons within the olfactory bulb
How do mitral cells of the olfactory bulb send their axons (anteriorly or posteriorly)?
posteriorly
How do mitral cells of the olfactory bulb send their axons posteriorly?
via the olfactory tracts into lateral and medial olfactory tract or stria
How do Olfactory neurons express a specific odorant receptor (and thus responsive to a specific odorant stimulus)?
project their axons precisely to a small number of glomeruli within the olfactory bulb (fidelity of odor detection)
Granule cells are _____ circuits and involve what?
1) inhibitory
2) synaptic plasticity
What is the lateral olfactory stria?
the projection bundle of fibers that passes laterally along the floor of the lateral fissure and enters the olfactory projection area in the temporal lobe
The lateral olfactory stria includes 3 what?
1) the pyriform
2) entorhinal cortex
3) parts of the amygdala
Where does the small medial olfactory stria pass?
passes medially and up near the inferior part of the corpus callosum
Where does the small medial olfactory stria carry the axons of some mitral cells to?
the anterior olfactory nucleus
What does the anterior olfactory nucleus do?
sends the axons of some mitral cells back to the olfactory bulbs on both sides (presumably as part of a feedback circuit that modulates the sensitivity of olfactory sensation)
Olfactory information from ______ ______ is relayed to the thalamus and proceeding to association areas in the neocortex
pyriform cortex
Where does further processing occur (of conscious discrimination of odors?
areas in the neocortex
The neural computations that occur in pyriform cortex regions influence what?
motor, visceral, and emotional reactions to chemosensory stimuli (particularly those relevant to feeding, reproduction, and aggression)
Entorhinal cortex receives inputs from what areas (4)?
1) amygdala
2) olfactory bulb
3) the limbic lobe
4) other cortical areas
Entorhinal cortex is the major source of what to what?
afferents to the hippocampus
In humans, olfaction is often considered the _____ acute of the sense.
least
What is anosmia?
the loss of the sense of smell (either total or partial)
The majority of individuals presented with ____ common odors can identify all seven correctly while people wit anosmia have difficulty identifying these common scents.
7
How can anosmia be aquired?
1) following chronic sinus infection or inflammation
2) traumatic head injury
3) exposure to toxins and aging
What does transient anosmia occur with?
a severe cold
Changes in the ability to identify 80 common odorants may reflect either ________ or _______ in otherwise typical (no additional neurological pathologies) aging individuals.
diminished peripheral sensitivity or altered activity of central olfactory structures
What is Often part of a battery of diagnostic tests administered at the early stages of age-related dementia and other neurodegenerative diseases?
University of Pennsylvania Smell Identification Test (UPSIT)
Olfaction is often compromised early in the course of what 2 diseases?
1) Parkinson’s
2) Alzheimer’s
Olfactory hallucinations (perception of a stimulus that is not actually present in the environment) are among the earliest symptoms of what?
schizophrenia
What are the causes of olfactory deficits in disorders?
not known
What kind of receptors are taste cells?
peripheral receptors
Where are taste cells found?
in taste buds distributed on the dorsal surface of the tongue, soft palate, pharynx, and upper part of the esophagus
What cranial nerve is the facial nerve?
CNVII
What cranial nerve is the lingual branch?
CN IX
The lingual branch is part of what nerve (give name, not cranial number)?
glossopharyngeal nerve
The superior laryngeal branch is part of the ____ nerve.
vagus
What cranial nerve is the vagus nerve?
CN X
What regions do the central axons of the primary sensory neurons project to?
the nucleus of the solitary tract in the medulla
trigeminal endings involves sensory information of what?
1) texture
2) spiciness
3) temp
Where is the ventral posterior medial nucleus located?
thalamus (which is located in the temporal lobe)
Where are taste buds distributed along?
1) the lateral surfaces of the papillar protuberance
2) in the trench walls
What do taste buds consist on?
1) specialized neuroepithelial receptor cells (called taste cells)
2) some supporting cells
3) basal cells
What does taste perception regenerate from?
basal cells (pool of stem cells in the tongue)
What part of the tongue is most receptive to sweet, umami, and salty compounds?
tip of tongue
Chemosensory transduction is initiated in the ______ domain of the taste cells, and electrical signals are generated at the basal domain via graded receptor
apical
What 3 things are part of sensory transduction in taste cells?
serotonin, ATP, and GABA
Voltage-regulated ion channels in taste cells are controlled by second messengers that are members of what family?
transient receptor potential (TRP)
Amiloride-sensitive Na+ channels respond to what taste?
salty tastes
What second messengers are part of the TRP family?
PKD channel, H+-permeant, nonselective cation channel
Taste cells transduce _________ _______ to encode information about the identity, concentration, and qualities (pleasant, unpleasant, or potentially harmful) of the substance.
chemical stimuli
The caudal part of the nucleus of the solitary tract also receives innervation from subdiaphragmatic branches of the _____ nerve.
vagus
subdiaphragmatic branches of the vagus nerve control what?
gastic motility
What connections can be through of as the sensory limb of a gustatory-visceral reflex arc?
interneurons connecting the rostral and caudal regions of the nucleus
The axons of the CNs terminate in the ______ tract
solitary
Where is the secondary neocortical taste area?
in the caudolateral orbitofrontal cortex
