48 Sensations of smell and taste

Question 1

The __________________ contains olfactory sensory neurons, lies on the dorsal and posterior nasal cavity

Answer 1

olfactory epithelium

Question 2

Why we can smell more during active sniffing compared to quiet sniffing?

Answer 2

Active sniffing increases fraction while during quiet breathing only a small portion of air reaches the olfactory epithelium.

Question 3

What are conchae? Why there is lost of sensation of smell during cold?

Answer 3

Highly vascular organs with erectile tissue on the surface of nasal cavity.

During cold, the conchae are engorged with blood, reduce amount of aim reaching the olfactory epithelium.

Question 4

Olfactory sensory neurons possess _______, on which specific odorant receptor molecules are located. They are short-lived, constantly being replaced by new cells derived from the _______________.

Answer 4

cilia;

basal stem cells

Question 5

Where are the cilia of the olfactory sensory neurons located? Why organic substances have strong smell to us?

Answer 5

Cilia are embedded in layer of lipid-rich mucus, secreted by the Bowman’s gland (therefore lipid soluble organic substances have strong smell to us)

Question 6

Odorant receptors are _______________receptors with 7 transmembrane domains.

Answer 6

G-protein coupled

Question 7

Each olfactory sensory neuron express ___________ odorant receptors.

Answer 7

one and only one

Question 8

Describe the chemoelectric transaction by odorant receptors.

Answer 8

• Opening of cyclic nucleotide-gated channels leads to the influx of Na+ and Ca2+ depolarising the cell.
• firing of the olfactory sensory receptors

(G-protein coupled receptor bind to odorant > AC > cAMP > bind to these channels)

Question 9

Why we cease to notice an odor after continuous exposure?

Answer 9

Adaptation, due to desensitisation of the odorant receptors

Question 10

Which of the following is true?
A. one odorant sensory neuron express one odorant receptor
B. one odorant molecule is detected by one odorant receptor
C. one odorant receptor may detect more than one type of odorant molecule

Answer 10

Only B is false

• one odorant molecule is detected by more than one receptors

Question 11

Olfactory neurons bearing the same olfactory receptors are spread across the olfactory epithelium but their axons converge to specialized synaptic regions in the olfactory epithelium called ______________.

Answer 11

glomerulus

Question 12

State the flow of events when odorant bind to receptors > bulb …

Answer 12

1. odorants bind to receptors
2. olfactory receptor cells are activated and send electric signals
3. the signals are relayed in the glomeruli
4. mitral cells in the bulb convey signals collected in glomeruli into CNS
5. transmitted signals to higher regions of the brain for recognition

Question 13

What are the main functions of the primary and secondary olfactory cortical areas?

Answer 13

Primary: for emotional aspects of olfactory sensation;
Secondary: for conscious discrimination of odors

Question 14

Give examples of the primary olfactory cortical areas.

Answer 14

1. Anterior olfactory nucleus
2. Entorhinal cortex
3. Amygdala
4. Piriform cortex
5. Olfactory tubercle

Question 15

Give examples of secondary olfactory cortical areas.

Answer 15

1. Orbitofrontal cortex (from thalamus)

2. Frontal cortex

Question 16

What is anosmia?

Answer 16

absence of smell

Question 17

What is the difference between hyposmia and dysosmia?

Answer 17

Hyposmia: diminish olfactory sensitivity;
Dysosmia: distorted sense of smell

Question 18

Reasons for common disorders of smell sensation?

Answer 18

1. absence/ disrupted functions of odorant receptors
2. associated with hypogonadism (Kallmann’s syndrome)
3. ageing: olfactory thresholds increases with age (alzhemiers, Parkinson’s)

Question 19

Name all types of papillae in different regions of the tongue. What do they all contain?

Answer 19

Anterior of tongue
1. Fungiform papillae
Posterior of tongue
2. Foliate papillae
3. Circumvallate papillae

all contain taste buds

Question 20

Which of the following is true?
A. Each taste bud contains one taste cell
B. Microvilli are present in the taste pores
C. Taste cells are long-lived, different from olfactory neurons

Answer 20

B only

A: each taste bud contains 50-150 taste cells
C: taste cells are short-lived and are constantly replaced by stem cells (basal cells) at the base

Question 21

What are the 4 types of taste and their chemoelectric transduction?

Answer 21

1. Saltiness: Na+ selective ion channels
2. Bitterness: Molecules block K+ channels directly
3. Sweetness: Bind to a few specific GPCRs for their actions
4. Sourness: direct entry of H+ through Na+ channels/ blockage of K+ channels

Question 22

A family of G-protein coupled receptors (GCRPs) bind most _________ molecules and generates intracellular
signaling molecule that modulate membrane excitability

Answer 22

bitter

Question 23

Gustatory pathway involves __________ and _________ in the pons. Then signals travel up to the _________________ nucleus of thalamus and lastly to the _____________cortex.

Answer 23

Nucleus of solitary tract;
gustatory area;
Ventral posterior medial;
Gustatory cortex (anterior Insula-frontal operculum)

Question 24

After reaching the primary olfactory cortex, taste signals will be sent to _______________.

Answer 24

Secondary gustatory cortical area in the orbitofrontal cortex

Question 25

The gustatory pathway is ipsilateral/ contralateral.

Answer 25

Ipsilateral

Question 26

What is ageusia?

Answer 26

absence of sense of taste

Question 27

What is the disorder for diminished taste sensitivity and distorted sense of taste respectively?

Answer 27

hypoageusia;

dysgeusia

Question 28

______________ may be the region to integrate olfactory and gustatory signal to generate final taste sensation

Answer 28

Orbitofrontal cortex

Question 29

Which nerve palsy may also impair taste sensation?

Answer 29

Facial nerve / Bell’s palsy;

because taste is the result of combination of taste, olfaction, temperature and somatosenation