A&P Exam 7: (3) Olfaction & Taste

Olfactory Epithelium - type of tissue? - type of cells?

*pseudostratified ciliated columnar epithelium* consisting of three kinds of cells: 1. *Olfactory Receptors* 2. Supporting cells (AKA sustentacular cells) 3. Basal stem cells

What cranial nerve serves the sense of taste for the... -anterior two-thirds of the tongue -posterior one-third of the tongue -throat -epiglottis

- Facial (CN VII) - Glossopharyngeal (CN IX) - Vagus (CN X) = *Throat AND epiglottis*

Where are receptors for taste sensations located?

- Located in *taste buds* - Most taste buds are on the tongue, but some can be found on the *soft palate, pharynx, and epiglottis*

For a given substance, compare the sensitivity of olfaction with the sensitivity of gustation. (R004)

-Olfaction and gustation are the *chemical senses* which WORK TOGETHER; stimulating molecules must be dissolved for perception -For the SAME CHEMICAL, *olfaction* is much *more sensitive* than taste

-What are the four traditional primary tastes? -What are the five modern-day primary tastes? (R060)

-Sweet, Sour, Salty, Bitter - 4 + *Umami*

Describe the function of *supporting cells, basal stem cells, and the olfactory glands* of the olfactory epithelium. (R016)

1. *supporting cells*: provide physical support, nourishment, and electrical insulation for olfactory receptors 2. *basal stem cells*: undergo continuous cell division producing NEW olfactory receptors (which live only 1 month) -- replacement is unusual since olfactory receptors are neurons 3. *Olfactory glands*: ducted glands (AKA Bowman's glands) produce mucus that moistens the olfactory epithelium and dissolves odorants

1. Which primary taste has the lowest threshold? 2. What is the threshold for sour substances relative to the other tastes? 3. Which primary taste requires the fewest molecules to activate it? (R075)

1. Bitter 2. Sour is somewhat higher than bitter, but still low 3. Bitter

1. Where are cell bodies of first-order neurons of the olfactory system located? 2. Where are cell bodies of second-order neurons of the olfactory system located? (R007, R035)

1. First-order neuron cell bodies: olfactory epithelium 2. Second-order neuron cell bodies: Olfactory bulb (anterior to "olfactory tract")

Correctly sequence the components of *olfaction* involving *G proteins* (second messanger)

1. Stimulus (odorant molecule) encounters the receptor 2. Activation of *adenylate cyclase* 3. Conversion of ATP to cAMP 4. Opening of Na+ channels 5. Na+ influx 6. Depolarizing *generator potential* develops 7. Nerve action potential

Describe the *pathway of olfaction* using the terms cranial nerve I, cribriform plate, first-order neuron, olfactory bulb, olfactory hair(s), olfactory tract, primary olfactory area, second-order neuron, transduction. (R006-R037)

1. Transduction at olfactory hairs 2. First-order olfactory receptor 3. Cribriform plate 4. Olfactory bulb 5. Second-order neuron 6. Olfactory tract 7. Primary olfactory area (conscious perception)

1. How many neurons comprise the olfaction pathway from transduction through primary olfactory area in the cerebrum? 2. How does this compare to the number of neurons in most sensory pathways that terminate in a primary sensory area in the cerebrum? (R036,Q023)

1. Two 2. Olfactory sensation is the ONLY sensation that reaches the cerebral cortex WITHOUT first synapsing in the *thalamus*; other axons on the olfactory tract project to the limbic system and hypothalamus, which accounts for emotional and memory-evoked responses to ordors

1. What are the three types of papillae that contain taste buds? 2. Which type is mostly lost during childhood? 3. Which type is mushroom-shaped? (R069)

1. Vallate papillae, Fungiform papillae, Foliate papillae 2. Foliate 3. Fungiform

Lack of the sense of smell

Anosmia - may be due to head injuries, nasal cavity inflammation (cold, allergies, smoking), physical obstruction (polyps), aging, *Zinc deficiency*, or genetic factors

- Taste associated with *poisonous foods* - Acute sensitivity (conventional receptor loction) on *back middle of tongue* (gag reflex)

Bitter

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *calcium ions released from internal stores*

Bitter Bitter substances cause release of Ca++ from internal stores (external Ca++ NOT required) --> transmitter is released, firing the primary afferent nerve

Where does the axon of an olfactory *receptor* terminate? (R035)

Bundles of unmyelinated axons of *olfactory receptors* extend through olfactory foramina in the cribriform plate of the ethmoid bone and comprise the *olfactory nerves (CN I)*, which then *TERMINATES in the olfactory bulbs* (paired masses of gray matter in the brain* -- the axon terminals of the first-order neurons (olfactory receptors) form sunapses with dendrites and cell bodies of *second-order neurons*

Taste adaptation??

Complete adaptation to a specific taste can occur in 1-5 minutes (a relatively brief period of time) of continuous stimulation

What type of papilla does not contain taste buds? What receptors do these papillae contain? (R069)

Filiform -- contains *tactile* receptors, but NOT taste buds

Distinguish between olfaction, flavor, and taste. Although these are different, how are they also interrelated? (R078)

Flavor = combination of taste (tongue) + odor (olfactory) - Volatile food chemicals are carried into the nasal cavity from behind as we eat (retronasal olfaction) brain combines taste and retronasal olfaction, creating *flavor*

Where are cell bodies of first-order neurons of the gustatory system located? (R080, K061)

Gustatory nucleus in the *medulla oblongata* -- from the taste buds, impulses propagate along the appropriate CRANIAL NERVE to the gustatory nucleus in the medulla oblongata

-What are the three kinds of neuroepithelial cells in taste buds? -What is the progression of these three cell types as precursors develop into successors? (R051)

Gustatory receptor cells Supporting cells (AKA sustentacular cells) Basal Cells Basal cells PRODUCE supporting cells, which DIFFERENTIATE into gustatory receptor cells (which have a 10-day life span)

reduced ability to smell

Hyposmia - may be associated with age, head injury, Alzheimer/Parkinson disease, smoking, drugs (antihistamines), analgesics and steroids

-Where are the first-order neurons of the olfactory pathway? -What structural type of neuron are they? (R007)

Olfactory receptors are *bipolar neurons* that are the first-order neurons of the olfactory pathway

Where is the gustatory nucleus located? (R081)

Medulla oblongata

Where is the olfactory epithelium located? (R006)

Millions of olfactory receptors are present in less than 1 sq in *olfactory epithelium*, which is in the *superior part of the nasal cavity* = *pseudostratified ciliated columnar epithelium*

A subtype of stem cell. When dividing this cell undergoes a proliferative division producing two identical cells. After that division, the daughter cells produce another identical daughter cells, as well as a non-stem-cell progenitor or a neuron by asymmetric divisons

Neuroepithelial cells

What causes different things to have different smells? (R012-R015)

Olfactory receptors respond to chemical stimulation of an odorant (chemicals that can stimulate the olfactory hairs) by producing a *generator potential*, initiating an *olfactory response*. 1. *slight molecular alterations* distinguish DIFFERENT odarants 2. *concentration differences* of the SAME substance can result in DIFFERENT odorants

What kind of graded potential is produced by gustatory receptors? (R079)

Receptor potential (NOT generator potential) stimulates exocytosis of synaptic vesicles from the gustatory receptor cells; the released NT trigger nerve impulses in the first-order sensory neurons that synapse with the gustatory receptor cell

- Taste associated with *sodium chloride* needed for diet - Acute sensitivity (conventional receptor loction) on *front sides of tongue* (just back and to the side of sweet, overlapping sweet

Salty

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *Na+ ions flowing into the cell*

Salty Na+ ions flow INTO the cell

What ION causes salty tastes? Sour tastes?

Salty: sodium chloride (Na+ ions) Sour: Acid foods (H+ ions)

- Taste associated with *spoiled foods* - Acute sensitivity (conventional receptor loction) on *back sides of the tongue*

Sour

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *protons flowing into the cell*

Sour Acidic (H+ protons flow INTO the cell)

Which tastes are initiated by the substance being tasted entering the taste receptor? (R063, R066, R072-R073)

Sour (H+ ions) Salty (Na+ ions)

What cranial nerve innervates olfactory glands of the olfactory epithelium? (R020)

Supporting cells and olfactory glands are innervated by branches of the *Facial Nerve (CN VII)*. Certain chemicals stimulate the nerve, causing tears and runny nose due to condequent action of the lacrimal glands and nasal mucous glands

- Taste associated with *safe foods* - Acute sensitivity (conventional receptor location) on the *tip of the tongue*

Sweet

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *adenylate cyclase*

Sweet

Which tastes are initiated by the substance being tasted binding with an integral membrane protein? (R062, R064, R067, R074)

Sweet Bitter Umami

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *neurotransmitter is released*

Sweet Bitter Umami NT is released...firing the primary afferent nerve

Of the different modes of transduction among the primary tastes, state which one (or ones) is (are) associated with: *Ca++ ions enter the cell through depolarization-activated calcium ion channels*

Sweet Sour Salty

What is the physiological function of saliva in gustation? (R056)

Tastants (chemical that stimulates gustatory receptor cells) must be dissolved (IN *SALIVA*) before they can be tasted

Describe the location of synapses of first-order gustatory neurons with second-order neurons. (R081)

Thalamus

What structure is formed by axons of second-order neurons of the olfactory system? (R036)

The *olfactory tract* -- axons project into the lateral olfactory area, which is the primary olfactory area (where conscious awareness of smell begins)

What is the site of olfactory transduction? (R009)

The cilia projecting from the dendrites of the olfactory receptor cells = *olfactory hairs* = sites of *olfactory transduction* (conversion of stimulus energy into a graded potential in a sensory receptor)

Are the olfactory bulb and olfactory tract components of the peripheral nervous system, or are they components of the central nervous system? (R035-R036)

The olfactory bulb and olfactory tract are NOT part of CN I, they are components of the CNS CN I = all of the Bundles of slender, unmyelinated axons of olfactory receptors taken together

What, or where, are the first-order neurons of the gustatory pathway? (R057, R079-R080)

Transduction creates a *receptor potential* that stimulates exocytosis of synaptic vesicles from the gustatory receptor cell The neurotransmitters trigger nerve impulses in the *first-order sensory neurons* that synapse with the gustatory receptor cell

- Taste associated with *amino acids* - Receptor location: diffuse (NO conventional location)

Umami

Retronasal olfaction vs. Orthonasal olfaction

Volatile food chemicals are carried into the nasal cavity from behind as we eat (and vice versa) brain distinguishes between the two because it keeps track of breathing out and in

What common feature is shared by tastants that *ENTER* the taste receptor through specific pores in the receptor membrane?

both release NT

What is the physiological function of mucus produced by the olfactory epithelium? (R019)

dissolves odorants and moistens the olfactory epithelium

What kind of graded potential is produced by olfactory receptors? (R004)

generator potential

Receptor produces a *reception potential*

gustation

Sites of taste transduction

gustatory hairs

Adaptation to odors

initially occurs rapidly (50% in the first few seconds) after stimulation -- after the first few seconds adaptation conintues, but at a slower rate

Receptor produces a *generator potential*

olfaction