chemical senses - jullet Flashcards
What is unique about the olfactory system?
information does not necessarily go through the thalamus on its way to the 6-layered cortex (unlike other sensory information)
What are the 3 parts of the nervous system dedicated to detecting chemicals in the environment?
1) trigeminal system, 2) olfactory system, 3) gustatory system
What is the function of the trigeminal system?
lingual branch innervates oral cavity; serves a protective function of detecting noxious and irritating compounds (ie vinegar, ammonia, capsaicin).
What is the sensitivity of the channels in the trigeminal system?
low affinity, low threshold (high sensitivity) receptors
What are TRP channels? What is an example of a TRP channel?
Transient Receptor Potential = TRP. Receptors that mediate sensations of pain, temperature, pressure, vision. Ex: Capsaicin receptor conveys sensations of heat and pain
What type of information do capsaicin receptors convey?
capsaicin receptor conveys sensations of heat and pain
Why is capsaicin used clinically as an analgesic and pain reliever?
Capsaicin receptor conveys sensations of heat via nociceptive fibers, where these channels are expressed. Chronic exposure of the capsaicin desensitizes the fibers, and that’s why it has been used clinically as an analgesic and pain reliever.
What is the sensitivity of the channels in the olfactory system?
high sensitivity (low threshold) + broad discriminatory powers (can distinguish thousands of different compounds)
T/F You can predict what a molecule smells like based on its structure.
False. There’s no way to predict what a compound will smell like based on its structure.
T/F The elderly has decreased olfaction compared to the youngins.
True. The ability to detect odors as we get older declines with age.
What are anosmias?
selective olfactory deficits for particular compounds (ie some people can’t detect butyl mercaptan (skunk odors))
The nasal cavity is composed of this epithelium.
RESPIRATORY epithelium with cilitated respiratory cells and goblet cells (mucus) and OLFACTORY epithelium, which contains CN1 olfactory neurons
Where are olfactory neurons localized in the nasal cavity?
in the olfactory epithelium - on the upper concha and part of the middle one. Their axons travel through the cribiform plate to synapse with the neurons in the olfactory bulb.
What are the 3 cell types of the olfactory epithelium?
1) basal cells, 2) support cells, 3) receptor cells
What are the roles of basal cells in the olfactory epithelium?
precursors of the receptor cell population that undergoes continual turnover
What are the roles of support cells in the olfactory epithelium?
provide (nutritional) support to receptor cells
Where can you find glomeruli?
olfactory bulb
What are mitral cells?
neurons in the olfactory bulb that synapse with CN1 (from the olfactory epithelium) and project to different regions of the brain.
What are the roles of receptor cells in the olfactory epithelium?
CN1 - soma with distal DENDRITES that project into the olfactory epithelium and unmyelinated AXONS that aggregate with other axons into FASICLES before becoming ensheathed in Schwann cells to form the OLFACTORY NERVE (which passes through the cribiform plate to synapse in the olfactory bulb)
What does the olfactory bulb contain?
it contains spherical structures called GLOMERULI, which are axonal endings of RECEPTOR CELLS (CN1) and MITRAL CELLS (neurons of the olfactory bulb that project to different regions of the brain).
What accounts for the sensitivity of the olfactory system?
large number of olfactory receptor neurons
What part of the receptor neuron plays a key role in olfactory transmission?
CILIA on receptor cells is where APs are generated (if odorants are applied to other areas of the cell or if the cilia are removed, most of the response is lost)
Odorant receptors are what type of receptors?
G-protein coupled receptors (GPCRs)
What is the (second messengers) transduction mechanism for odorant receptors on the cilia of receptor cells? (3)
1) cAMP, 2) Ca2+, or 3) IP3 induces gated channels to open.
T/F If you administer an inhibitor of adenylate cyclase, you abolish all sense of smell.
False. There is more than one transduction mechanism that receptor cells use to convey olfactory stimuli (ie cAMP, Ca2+, IP3)
T/F Individual receptor cells express several types of receptor types.
False. They express one or a small number of receptor types. (there are large families of olfactory receptor genes in animals that contribute to the broad discriminatory powers of olfactory systems)
T/F Receptor neurons expressing the same odorant receptor converge in the same glomerulus.
True. This type of integration may be a point of comparison and discrimination and may contribute to sensitivity.
What is the across fiber pattern theory?
quality of an odorant compound is encoded/determined by the simultaneous pattern of activity across many receptor cells, rather than a single receptor cell
How does central processing in the olfactory cortex occur?
cortical neurons receive inputs from more than one glomerulus, which allows them to integrate inputs from multiple olfactory receptor proteins
What are “comparsion neurons” in the olfactory cortex?
they are cortical neurons that respond to a mix of two odorants but are not stimulated by either of the odorants when presented individually. Helps to discriminate among different odorants or create a novel smell that is unlike either of the two odorants in the mixture
How is olfactory information transmitted to the CNS?
Information from the RECEPTOR CELLS is transmitted to the MITRAL CELLS, which then projects to the PIRIFORM cortex near the optic chiasm and temporal lobe.
What are the olfactory bulb targets?
piriform cortex, olfactory tubercle, amygdala, entorhinal cortex
When olfactory information is transmitted from the amygdala to the hypothalamus, how is the information coded?
emotional and motivational aspects of odor sensations
When olfactory information is transmitted from the thalamus to the frontal lobe, how is the information coded?
conscious olfactory perception and discriminations
When olfactory information is transmitted from the entorhinal cortex to the hippocampus, how is the information coded?
memory and emotional responses coupled to particular odors
How are olfactory information modulated? (2)
1) emotional state (fear/excitement) enhances sense of smell through adrenergic/EPI fibers, 2) locus ceruleus (motivation/hunger) enhances sense of smell through NE fibers
What is umami?
taste of L-glutamate (MSG); helps signal the presence of protein-rich foods
Where are taste receptor cells found?
papillae on the surface of tongue.
What are the 4 types of papillae?
1) Filoform, 2) Circumvallate, 3) Foliate, 4) Fungiform.
What type of taste papillae do not have taste buds on them?
filoform
Where can you find circumvallate papillae and what are they innervated by?
across the back of the tongue; innervated by CN IX
Where can you find foliate papillae and what are they innervated by?
back edges and side of tongue; innervated by CN VII and IX
Where can you find fungiform papillae and what are they innervated by?
scattered across the entire surface of tongue; innervated by CN VII
Each taste bud has 3 cell types.
1) basal cells, 2) support cells, 3) receptor cells (similar to olfactory system)
How are receptor cells in the gustatory system different than those in the olfactory system?
Receptor cells in the gustatory system do not have axons that convey information centrally. Instead, they are secondary sensor cells.
What are the 3 cranial nerves that innervate the taste buds?
CN VII (fungiform), CN IX (circumvallate/foliate), and CN X
How is gustatory information projected from the tongue to the CNS?
From the tongue, projections go to the nucleus of the solitary tract (NST) in the brainstem, and then to the VPM of the thalamus, and then finally to the gustatory cortex, in the temporal lobe near the insula, and the hypothalamus and amygdala.
What is the nucleus solitary tract (NST)?
Area in the brainstem where CN VII, IX, and X from the tongue project to. Axons from the NST project to the VPM of the thalamus, which then projects to the gustatory cortex.
Where does gustatory information project to in the CNS?
insula (underneath the temporal lobe), near the somatosensory cortex where tactile information from the tongue, mouth, and throat are received.
Other than the insula, where else does gustatory information project to?
to limbic areas of the brain (hypothalamus/amygdala); and is responsible for the visceral and emotional responses to taste.
How is gustatory information coded in the cortex?
individual neurons in the gustatory cortex may respnod to ≥1 tastants and individual tastants elicit distinct, yet overlapping response patterns in the insula; purpose may be to discriminate among various tastants.
Which part of the tongue detects bitter stuff? Type of papillae involved? Innervation?
back (Bitter = Back); contains circumvallate papillae, CN IX
Which part of the tongue detects sour stuff? Type of papillae involved? Innervation?
side (Sour = Side); contains foliate, CN IX
Which part of the tongue detects sweet/umami and salty stuff? Type of papillae involved? Innervation?
tip of tongue
What type of neurotransmitter does tastebuds secrete?
ATP or serotonin
In taste receptor cells that detect salt, what type of receptor is it? What are the properties of this receptor? What is the (second messengers) transduction mechanism?
VG Na channels; constitutively OPEN. Large increase in extracellular Na drives Na into the cell, which causes depolarization of the taste receptor cell. Leads to Ca entry from extracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.VG Na channels; constitutively OPEN. Large increase in extracellular Na drives Na into the cell, which causes depolarization of the taste receptor cell. Leads to Ca entry from extracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.
In taste receptor cells that detect sour, what type of receptor is it? What are the properties of this receptor? What is the (second messengers) transduction mechanism?
Cation-selective ion channels open in response to H+ (sour taste is produced by acids) and cause depolarization of the taste receptor cell. Leads to Ca entry from extracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.Cation-selective ion channels open in response to H+ (sour taste is produced by acids) and cause depolarization of the taste receptor cell. Leads to Ca entry from extracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.
In taste receptor cells that detect sweet, what type of receptor is it? What are the properties of this receptor? What is the (second messengers) transduction mechanism?
G-protein coupled receptors that open in response to sweet molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.G-protein coupled receptors that open in response to sweet molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.
In taste receptor cells that detect bitter, what type of receptor is it? What are the properties of this receptor? What is the (second messengers) transduction mechanism?
G-protein coupled receptors that open in response to sweet molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.G-protein coupled receptors that open in response to sweet molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.
In taste receptor cells that detect umami what type of receptor is it? What are the properties of this receptor? What is the (second messengers) transduction mechanism?
truncated metabotropic glutamate receptors (G-protein coupled receptors) that open in response to umami molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.truncated metabotropic glutamate receptors (G-protein coupled receptors) that open in response to umami molecules and cause depolarization of the taste receptor cell. Leads to increase PIP2/IP3 and Ca entry from intracellular stores and vesicle fusion, and subsequently neurotransmitter (ATP/serotonin) release.
What is the labeled line hypothesis?
information from individual receptors that are sensitive to specific classes of tastants (salt, sour, umami, etc) is carried on segregated pathways to the brain.
How is the labeled line hypothesis different than the across fiber pattern in olfaction?
LABELED LINE: information from individual receptors that are sensitive to specific classes of tastants (salt, sour, umami, etc) is carried on segregated pathways to the brain. ACROSS-FIBER PATTERN: olfaction (quality of an odorant) is encoded by the simultaneous pattern of activity across many receptor cells, rather than a single receptor cell
What 4 compounds modulate taste receptor cell sensitivity?
Serotonin (5HT) and Cholecystokinin (CCK) enhances taste receptor cell responses. Aldosterone and Vasopressin enhances taste cell responses to NaCl.
How does atrophic rhinitis affect olfactory and/or gustatory abilities?
reduced olfactory abilities
How does diabetes affect olfactory and/or gustatory abilities?
reduced olfactory abilities
How does alzheimers disease affect olfactory and/or gustatory abilities?
reduced olfactory abilities
How does chronic renal failure affect olfactory and/or gustatory abilities?
reduced olfactory + gustatory abilities
How does cystic fibrosis affect olfactory and/or gustatory abilities?
enhanced olfactory + gustatory abilities
How does epilepsy affect olfactory and/or gustatory abilities?
enhanced olfactory + gustatory abilities
