Smell and Taste- Heinbockel

Question 1

What are the two chemical senses?

Answer 1

• olfaction

- gustation

Question 2

Both taste and smell chemoreceptors respond to chemicals in what?

Answer 2

aqueous solutions

Taste – to substances dissolved in saliva

Smell – to substances dissolved in fluids of the nasal membranes

Question 3

The olfactory system deals with volatile or nonvolatile substances? What about the gustatory system?

Answer 3

olfactory system: general odors, VOLATILES, pheromones (food, predators, mating and aggression cues, individual identity)

Gustatory system – NONVOLATILES (sweet,
bitter, salty, sour, umami tasting substances)

Question 4

What do the chemical senses need to do?

Answer 4

• Detect all relevant chemicals in the environment (including novel ones)
• Encode both QUALITY and QUANTITY of individual chemicals in the context of complex chemical mixtures; when you smell smoke it is not just one type of chemical but a mixture of different chemicals
• Decode and interpret this sensory information in the context of experience and other sensory input so that the nervous system can generate an appropriate behavioral response

Question 5

What factors do the chemical senses encode in the chemicals?

Answer 5

both quality and quantity

Question 6

From the Nose to the
Olfactory Bulb and on to
Higher Olfactory Centers

Answer 6

Olfactory receptor neurons (ORNs), typical bipolar neurons, are found in an epithelial sheet in the nasal epithelium

ORNs project axons (CN I) to the ipsilateral olfactory bulb
Synaptic interactions occur within glomeruli in the bulb.

Olfactory bulb neurons interact with central neurons (mitral and tufted cells) which send axons to olfactory cortex and other structures in the limbic system

axons travel through nasal epithelium to cribriform plate to olfactory bulb

Question 7

Where is the olfactory epithelium?

Answer 7

on the superior concha in the nasal cavity

Question 8

Describe the olfactory pathway.

Answer 8

Air and odorant molecules come in and go to the back of the nose where they activate olfactory receptor neurons through cilia (has membrane proteins) binding the molecules

the axons all together form CN I and go through the cribriform plate to the olfactory bulb where they synapse on central neurons like the mitral cells that will go to higher olfactory centers (olfactory cortex or limbic system)

ORNs project to the olfactory bulbs and synapse with mitral cells

Glomerular mitral cells process odor signals

Mitral cells project axons and send impulses to the olfactory cortex (anterior olfactory nucleus, piriform cortex, olfactory tubercle), amygdala, and entorhinal cortex

Secondary projections go to the thalamus, hypothalamus, and hippocampus

Question 9

Where does olfactory transduction takes place where?

Answer 9

on the cilium at the end of dendrites of the olfactory receptor neurons (has specific membrane proteins and is bathed in serous fluid)

Question 10

What are the two types of cells in the nasal epithelium?

Answer 10

• supporting cells (sustentacular cells)
• stem cell population of basal cells; need them due to the rapid turnover rate of olfactory receptor neurons (live only for months or two)

Question 11

While olfactory receptor neurons have cilia, what do the supporting cells in the nasal epithelium have?

Answer 11

microvilli

Question 12

Describe olfactory receptor neurons.

Answer 12

-odors interact with olfactory receptor neurons (ORNs) at the dendritic cilia

• these cilia contain the molecular components of the sensory transduction cascade
• ORNs are bipolar neurons with cilia
• ORNs send axonal projections to the olfactory bulb-supporting cells have microvilli

Question 13

Why do olfactory receptor neurons have a short lifespan of 30-60 days?

Answer 13

constantly bombarded with air and odor molecules

Question 14

How are ORN regenerated?

Answer 14

new cells generated by the stem cell population (basal cells) in the nasal epithelium

basal cells contain progenitor and stem cell populations–migrate, differentiate and replace ORNs and other OE cell types

Question 15

What is interesting about the new ORN generated by the basal cells in the nasal epithelium?

Answer 15

the “new” ORN forms new connections in the olfactory bulb

they produce axons that project to the olfactory bulb; they know exactly where to go

Question 16

Where does the watery fluid that bathes the cilia of ORNs come from?

Answer 16

secreted by olfactory (Bowman’s gland)

Question 17

What is the arrangement of cilia in the respiratory system vs those in the olfactory system? Why is this arrangement important?

Answer 17

few nonmotile cilia in the olfactory system (just there to bind to air and odor molecules)

9 plus 2 arrangement (motile) cilia in the lower respiratory system (trachea and bronchi) important for moving material out of the airway

Question 18

We have a Large Family of

Odorant Receptors that are of what type?

Answer 18

g protein coupled receptors

Each receptor consists of a protein chain that traverses the cell membrane seven times. When an odorant substance attaches to an olfactory receptor, the shape of the receptor protein is altered, leading to a G protein activation. An electric signal is triggered in the olfactory receptor neuron and sent to the brain via nerve processes.

Question 19

What is the unexpected finding in terms of the expression of the olfactory receptors?

Answer 19

Every single olfactory receptor cell expresses one and only one gene of all the genes that code for olfactory receptor molecules.

Each olfactory receptor cell expresses one type of odorant receptor, and each receptor can detect a limited number of odorant substances.

Question 20

Explain why the olfactory receptors are triggered by different odorant molecules.

Answer 20

All odorant receptors are related proteins and differ only in some amino acid residues. The subtle differences in the protein chains explain why the receptors are triggered by different odorant molecules.

Question 21

How are the different olfactory receptors arranged in the nasal epithelium?

Answer 21

There are separate zones of the olfactory epithelium. A different set of odorant receptor genes is expressed in each zone.

Question 22

How many different odorants can be distinguished?

Answer 22

350

Question 23

What allows us to detect many odorants that outnumber the amount of olfactory receptors we have?

Answer 23

a given olfactory receptor is activated by several odorants and a given odorant can activate different types of olfactory receptors

Question 24

Describe the olfactory transduction.

Answer 24

Odors are transduced by a G Protein-coupled cascade

the odorant binds to the odorant receptor in the cilia of the dendrites of the olfactory receptor neurons which activates the G protein.

the alpha subunit (Galphaolf) activates the adenylate cyclase which makes cAMP from ATP

the cAMP activates the cyclic nucleotide gated channel that allows sodium and calcium to rush into the cell which depolarizes the cell leading to an AP

-the incoming calcium also opens up the chloride anion channel making the inside of the cell more positive (making chloride leave the cell) allowing for further depolarization

another pathway is the (inositol triphosphate pathway) IP3 pathway

Question 25

What are the major molecular components of the olfactory transduction cascade?

Answer 25

-Olfactory receptor (OR)--member of the G-protein coupled receptor family (7TMs), there are ~900 functional OR genes in mouse, ~400 in humans - G protein--couples OR to ACIII, includes Golf a-subunit - Adenylyl cyclase type III--synthesizes the second messenger cAMP -CNG channel--gated by cAMP, contributes to depolarization of the ORN and Ca2+ influx (underlies both additional activation of Ca2+-sensitive Cl- conductance and odor adaptation through negative feedback) -Ca2+-sensitive Cl- channel--has not been cloned, contributes majority of depolarizing current

Question 26

Not all the genes are expressed throughout the entire olfactory epithelium. Certain genes are expressed only in cells in a given zone or region. How many zones are there and what is represented in each?

Answer 26

4 zones Zone I Zone II Zone III Zone IV

Question 27

Describe the intrinsic organization of the olfactory bulb.

Answer 27

-Convergent Projection Pattern of Olfactory Sensory Neurons to the Main Olfactory Bulb - 2,000 glomeruli - Each glomerulus also contains branched dendrites of mitral and tufted cells - 1 ORN for 1 olfactory receptor gene for 1 glomerulus ORNs expressing a given receptor protein converge onto the same glomerulus AKA onto only a few individual glomeruli in the bulb

Question 28

What is the first relay station in brain | for the processing of olfactory information?

Answer 28

olfactory bulb

Question 29

The ORN axons enter the olfactory bulb and end in structures called what?

Answer 29

glomeruli

Question 30

What are the output neurons of the olfactory bulb?

Answer 30

mitral and tufted cells

Question 31

State the relative amount of projection from the olfactory bulb to higher olfactory centers and vice versa.

Answer 31

There are more axons going down to the olfactory bulb from the higher olfactory centers than those going from the olfactory bulb to higher olfactory centers Modulation of bulb activity is done by descending (centrifugal) circuits.

Question 32

What is the purpose of inhibitory interneurons?

Answer 32

mediate lateral inhibition by connecting mitral and tufted cells of other input channels (banana smell more enhanced than the apple smell)

Question 33

Compare the input into the olfactory bulb to that of the olfactory cortex.

Answer 33

convergence to the olfactory bulb and divergence to the olfactory cortex

Question 34

Tracing the olfactory Pathway

Answer 34

- 5 million olfactory sensory neurons - 1000 different odorant receptor genes - 2000 glomeruli in the olfactory bulb - 1 olfactory receptor neuron - 1 odorant receptor- 1 glomerulus

Question 35

What does the olfactory cortex consist of?

Answer 35

- anterior olfactory nucleus - piriform cortex - olfactory tubercle - amygdala - entorhinal cortex

Question 36

Where do secondary projections of the olfactory pathway go to?

Answer 36

thalamus , hypothalamus, hippocampus

Question 37

# Define the following olfactory disorder: - anosmia - hyposmia - dysosmia - phantosmia

Answer 37

Anosmia (loss of smell) hyposmia (diminished smell) -both result from a number of etiologies Dysosmia (distorted smell) phantosmia (phantom smells = smelling something that is not really there) -may accompany conditions such as prior URI, nasal/sinus diseases, head trauma, aging

Question 38

How does head trauma result in anosmia?

Answer 38

hard hit to the nose: -all the axons reaching through the cribriform plate will be torn as the nose is displaced resulting in no sense of smell the axons no longer have connections to the olfactory

Question 39

Taste primarily occurs where?

Answer 39

on taste buds on the tongue Taste buds are found in papillae of the tongue mucosa

Question 40

What are the different types of taste buds (papillae) on the tongue?

Answer 40

circumvallate: really big foliate: leaf fungiform: mushroom filiform: really thin

Question 41

How is the sense of taste organized on the tongue?

Answer 41

in the taste buds are receptor cells which can detect the different taste qualities so you can taste anything anywhere on the tongue there is not region of the tongue set out for a particular taste like sweet for example

Question 42

What are the different type of cells found in each gourd-shaped taste bud and what are their functions?

Answer 42

gustatory cells: supporting cells: insulate the receptor basal cells: dynamic stem cells

Question 43

Are the gustatory receptors neuronal in origin?

Answer 43

are not neuronal cells but epithelial in origin thus they have no axons but they do have cranial fibers that go right up the taste buds form chemical synapse on sensory fibers and voltage gated ion channels to generate action potentials

Question 44

Where does taste transduction take place?

Answer 44

on gustatory hairs, microvilli, exposed to oral cavity

Question 45

Where are taste buds located?

Answer 45

in papillae on the tongue (also in epithelium of soft palate, nasopharynx, and epiglottis)

Question 46

The taste bud contains what different kinds of taste receptor cells?

Answer 46

Type I Type II Type III taste receptor cells -all with modified epithelium

Question 47

What is the function of the basal cells in the taste buds? What is the lifespan of taste receptor cells?

Answer 47

- basal cells give rise to new receptor cells | - lifespan of TRC is 10 days (shorter than olfactory receptor cells) as they are constantly bombarded with food

Question 48

What are the five basic taste sensations?

Answer 48

Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate

Question 49

Explain the overall characteristics of taste transduction.

Answer 49

Taste stimuli are transduced by a G protein-coupled cascade Have G-couple protein receptors (taste receptor) and membrane proteins that allow certain ions to get into the cell signal transduction that involves calcium channels there are no axons but there is neurotransmitter release onto the primary sensory neurons onto some cranial nerve fibers

Question 50

Describe the process of taste transduction.

Answer 50

taste stimulus binds to taste receptors which activates g protein that activates phospholipase C which then generates diacylglycerol (DAG) and IP3 transient receptor potential (TRP): new class of ion channels involved in sensory functions -sodium and calcium rushing into the cells and additional IP3 receptors that evoke calcium release

Question 51

What are the different taste transduction mechanism?

Answer 51

some of the atse (bitter, sweet, umami) work through a g-protein coupled mechanism some other (sour and salty) use other mechanisms they all converge o a common signal in the center in that the cell get depolarized (either calcium rushing in or closing sodium channels) and release of NTs

Question 52

Describe the taste transduction for salty and sour taste.

Answer 52

The stimulus energy of taste is converted into a nerve impulse by: - Salty & sour involve permeation, or blockade, of ion channels - Na+ influx in salty tastes - H+ in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K+ channels) - Sweet & bitter tastes mediated by G protein-coupled mechanisms or direct effects on ion channels - Gustducin (G protein) in sweet and bitter tastes - Umami: metabotropic glutamate receptor-mediated (very acting glutamate receptor)

Question 53

In order for a chemical to activate the taste receptor AKA be tasted, what needs to occur?

Answer 53

taste (food) must be dissolved in saliva and contact the gustatory hair cells Binding of the food chemical: - Depolarizes the taste cell membrane, releasing neurotransmitter - Initiates a generator potential that elicits an action potential in the cranial nerve fibers

Question 54

Describe the gustatory pathway.

Answer 54

depending on where you are in the tongue you are activating different types of cranial nerves (either facial, glossopharyngeal, or vagus) irrespective of which cranial nerve gets activated here they all project to the nucleus solitarius in the medulla oblongata and from there they project to the thalamus (in the olfactory system thalamus is INDIRECTLY involved) to go to the gustatory cortex Cranial Nerves VII (branch of facial nerve, chorda tympani) and IX (lingual branch of glossopharyngeal nerve) carry impulses from taste buds to the solitary nucleus of the medulla

Question 55

Which higher order brain centers receive fibers from the thalamus in the gustatory pathway?

Answer 55

- Cortex (insular or gustatory cortex) (taste) - Amygdala (central nucleus) (appreciation of taste) - Hypothalamus (lateral hypothalamic nucleus) to brainstem reticular formation structures - -> control salivation, insulin release and relevant musculature (tongue, face muscles, swallowing muscles)

Question 56

List the cranial nerve associated with each of the following: - soft palate - epiglottis - vallate papillae - foliate papillae - fungiform papillae

Answer 56

- soft palate: VII - epiglottis: X - vallate papillae: IX - foliate papillae: IX, VII - fungiform papillae: VII

Question 57

How is taste and olfaction related to one another?

Answer 57

there is another pathway that makes us think that smell is really involved - Taste is 80% smell, retronasal activation (odors from the food you taste on your tongue go to the olfactory receptors so when you can't smell you can taste your food) - Thermoreceptors, mechanoreceptors, nociceptors also influence tastes - Temperature and texture enhance or detract from taste - Taste is in the mouth, not in the nose - Coincidence of somatosensory stimulation of tongue and retronasal passage of odorants into nose --> odorants are perceived as flavors in mouth