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Olfaction & Taste Flashcards

1
Q

Describe the intranasal chemosensory systems. Which cranial nerves play a part and what are their functions?

A

Cranial Nerve 0 = “Nervus Terminalis”
- CN0 rests on the anterior surface of the brain in the region of the olfactory trigone and courses anteriorly on the medial surface of the olfactory tract and bulb
- Animal pherome receptor
- Releases gonadotropin releasing hormone (rudimetary in humans)
- The vomeronasal organ (Jacobson’s Organ) is the organ that has afferents to CN0 and leads to the accessory olfactory bulb
- In humans, it is a rudimentary structure on the nasal septum

Cranial Nerve I = Olfactory Nerve
- 50+ nerve bundles in the olfactory epithelium
- Involved in smell and taste transduction

Cranial Nerve V = Trigeminal Nerve
- Somatosensory aspects of smell, such as irritants, temperature sensations, pungency
- High irritant concentrations can induce reflex responses

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2
Q

Describe the anatomy of the olfactory mucosa. What are the cells in the olfactory epithelium?

A

Olfactory mucosa is comprised of:
1. Olfactory Neuroepithelium (OE)
2. Lamina Propria (deep to the OE)

CELLS IN THE OLFACTORY NEUROEPITHELIUM
1. Basal cells
- Olfactory stem cells which can regenerate olfactory receptor neurons
- Divided into:
- Globose Basal Cells = Routinely replenish
- Horizontal Basal Cells = Dormant unless activated by tissue injury
2. Olfactory Receptor Neurons
- Specialized bipolar neurons (neuron that has two extensions)
- Cell bodies located in the olfactory neuroepithelium. 1 dendrite goes towards the epithelial surface. 2nd dendrite passes through basement membrane where they form bundles with olfactory ensheating cells
- These bundles are called “Fila”, which collectively form the olfactory nerve
- Contain cilia to increase surface area, lack dynein arms and do not beat
3. Supporting (Sustenacular Cells)
- Also contain microvilli
- Insulate bipolar cells, deactivate odorants, protect epithelium from foreign agents, regulate mucous composition
4. Microvillar Cells
- 1/10th as frequent as bipolar cells, may have a receptor function (unknown currently)
5. Duct cells
- Carry mucous to the epithelial surface
- Connect to Bowman’s Glands in the lamina propria

CELLS IN THE LAMINA PROPRIA:
1. Bowman’s Glands (Produces mucus to moisten the olfactory epithelium and dissolve odour-containing gases.)
2. Olfactory Ensheathing cells (OECs - unique cells that are responsible for the successful regeneration of olfactory axons throughout the life of adult mammal).

Mnemonic for the OE cells: BOSS MD
B: Basal Cells
O: Olfactory Receptor Neurons (bipolar cells)
SS: Supporting Sustenacular cells
M: Microvillar cells
D: Duct cells

https://pub.mdpi-res.com/ijms/ijms-22-06311/article_deploy/html/images/ijms-22-06311-g001.png?1624236058

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3
Q

Describe the Ascending Pathway of the Olfactory System

A
  1. Olfactory Receptor Neurons (ORNs) are Bipolar (1 dendrite to nasal mucosa, other past the basement membrane into lamina propria)
  2. ORNs combine with olfactory ensheathing cells in the lamina propria to form bundles called “FILA”
  3. Bundles together collectively form the “OLFACTORY NERVE”
  4. Olfactory nerve passes through foramina in the cribriform plate
  5. Olfactory nerve then synapses with second order neurons in the ipsilateral “OLFACTORY BULB”
  6. Second order neurons are called “MITRAL CELLS” and “TUFTED CELLS”. They lie in specialized organs called “GLOMERULI”
  7. Tufted Cells - extend to Anterior olfactory nucleus, anterior perforated substance
  8. Mitral Cells - extend to Anterior olfactory nucleus, piriform cortex, amygdala, and rostral entorhinal cortex

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https://mammothmemory.net/images/user/base/uncategorised/1.31.13%20Olfactory%20system%20diagram.jpg

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4
Q

What are the 5 layers of the histology of the Olfactory Bulb

A
  1. Glomerular Layer
    - Contain Juxtaglomerular cells (role in olfactory information processing)
    - Contain glomeruli which are where the ORNs synapse with the mitral and tufted cell bodies
  2. External plexiform Layer
    - Contain tufted cell bodies
  3. Mitral Layer
    - Contain mitral cell bodies
  4. Internal Plexiform Layer
  5. Granule Cell Layer
    - Contains granular cells (inhibitory interneurons and control the neural activity of excitatory projection neurons)

Note:
- Synapses are mostly GABAergic and Dopaminergic
- ~40 olfactory nerve cell bodies in the cribriform

GEMIG

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https://images.app.goo.gl/TepJTTfrbtWsada37

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5
Q

What are the central olfactory connections? 7

A

Primarily in the medial temporal lobe:
1. Prepyriform cortex
2. Periamygdaloid cortex
3. Olfactory tubercle
4. Lateral entorhinal cortex
5. Amygdaloid nucleus
6. Nucleus of the terminal stria
7. Dentate and semilunate gyri

POP LAND

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6
Q

What are the Structures of the Primary Olfactory Network?
What are the structures of the secondary olfactory network?

A

Primary Mnemonic: AA-EPA

A: Anterior Olfactory Nucleus (conscious perception of smell)
A: Amygdala (emotional response)
E: Entorhinal Cortex
P: Piriform Cortex
A: Anterior perforated substance

Secondary/Tertiary:
1. Orbitofrontal cortex
2. Anterior insula
3. Mediodorsal Thalamus
4. Hypothalamus
5. Para-hippocampus (olfactory memory)
6. Ventral pallidum
7. Ventral striatum

+ Reticular formation - visceral responses to smell

“Oooo A Hippo, he smells bad! THAlia THAlia get me TWO VENTI starbucks please!”

Pathways:
Olfactory Epithelium –> Olfactory Bulb –> Olfactory Tract –> Primary Olfactory Network –> Secondary/Tertiary Olfactory Network

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7
Q

What is adult neurogenesis in the context of the olfactory system?

A

Olfactory receptor neurons (ORNs) are unique in that they communicate directly with both the external environment and the CNS. This makes them prone to exogeneous damage.

As a result, the ORNs are unique in that they have adult neurogenesis. ORNs are regenerated from basal cells

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8
Q

What is the olfactory cleft? What are its boundaries?

A

Olfactory clefts = two narrow vertical passages at the upper part of the nasal cavities and constitute a crucial pathway for airborne odorant molecules to the olfactory mucosa

Boundaries:
- Superior = Cribriform plate
- Lateral = Superior turbinate
- Medial = Superior septum

The olfactory neuroepithelium spans an area of around 2-5 cm^2.

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9
Q

What are 3 differences between olfactory and respiratory epithelium?

A
  1. Olfactory epithelium is thicker (60-70nm) than respiratory epithelium (20-30nm)
  2. Olfactory cilia lack dynein arms (non-motile)
  3. Olfactory epithelium gets 15% of nasal airflow (consequently, during normal breathing, less than 15% of the total inspired nasal air will reach the epithelium), while the remainder of the respiratory epithelium gets 50%

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10
Q

What is the histology of the olfactory neuroepithelium?

A

Pseudostratified columnar epithelium

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11
Q

Where is the olfactory neuroepithelium located in the nose?

A
  • 10 x 10mm
  • Medial surface of the superior turbinate
  • Medial surface of the middle turbinate
  • Undersurface of the cribriform plate (~15%)
  • Upper nasal septum (biopsy here if needed)
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12
Q

Describe the olfactory transduction mechanism

A
  • Odorants are solubilized in mucous (hydrophilic), or by Odorant binding protein (OBP) (hydrophobic)
  • G-protein coupled receptors (~1000, 1% of expressed genes)
  • Second messenger = cAMP
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13
Q

Define ortho and retronasal olfaction.

A

Orthonasal olfaction: Odorants travel from the nasal cavity backwards

Retronasal olfaction: Odorants travel in a retrograde fashion (more marked during eating and drinking), which is more marked during the oral and phyarngeal stages of swallowing.

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14
Q

What are the two classifications of smell disturbances?

A

QUANTITATIVE:
1. Anosmia
2. Hyposmia
3. Hyperosmia

QUALITATIVE (DYSOSMIA)
1. Parosmia/Cacosmia
2. Phantosmia
3. Agnosmia

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15
Q

Define the following terms:
1. Normosmia
2. Hyposmia
3. Functional Anosmia
4. Anosmia
5. Parosmia/Dysosmia
6. Hyperosmia
7. Phantosmia
8. Agnosmia
9. Specific Anosmia

A
  1. Normosmia: normal olfactory function
  2. Hyposmia (Microsmia): Quantitatively reduced olfactory function < 10% population
  3. Functional Anosmia: Quantitatively reduced function to the point where there is no useful function in daily life
  4. Anosmia: Absence of all olfactory function
  5. Parosmia (Dysosmia, Cacosmia, Euosmia, Troposmia): Distorted perception of odors
  6. Hyperosmia (Superosmia): Quantitatively increased ability to smell odours to an abnormal level. Very rare but described in e.g. migraines, post-ictal state
  7. Phantosmia: Perception of an odour that is not present
  8. Agnosmia: Inability to recognize an odour
  9. Specific Anosmia (Partial anosmia): Quantitatively reduced ability to smell a specific odor despite preserved ability to smell most other odors. Thought to be a normal physiologic trait with little clinical significance
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16
Q

What is the classification of hyposmia/anosmia?

A
  1. Conductive: Access of odorant changed
  2. Sensory: Damage to olfactory nerve
  3. Neural: Damage to central olfactory pathways
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17
Q

List a complete differential diagnosis of olfactory dysfunction

A

A. CONGENITAL
1. Kallman’s
2. Familial anosmia (autosomal dominent, premature baldness, vascular headaches)

B. OBSTRUCTIVE NASAL DISEASE (23%)
1. Polyps
2. Edema
3. Tumors
4. Nasal deformity

C. IDIOPATHIC (21%)

D. POSTINFECTIOUS (19%)
1. Viral injury to olfactory neurons

E. HEAD TRAUMA (15%)
1. Shearing of filaments
2. Olfactory bulb contusion
3. Frontal lobe injury

F. NEUROLOGIC
1. Parkinson’s
2. Alzheimer’s
3. Multiple sclerosis

G. PSYCHOGENIC (e.g. Schizophrenia)

H. TOXINS/MEDICATIONS (3%)
1. Smoking - recovery after quitting smoking is dependent on pack years and time since cessation
2. Formalin
3. Zinc in nasal sprays (banned now by FDA)

I. NEOPLASTIC
1. Foster-Kennedy syndrome

J. AGING

18
Q

Most common causes of sensorineural hyposmia?

A
  1. Head trauma
  2. URTI
19
Q

What neurological disorders are most associated with hyposmia?

A
  1. Early symptom of Alzheimer’s and Parkinson’s
20
Q

What are 5 causes of hyperosmia?

A
  1. Pregnancy
  2. Migraines
  3. Cluster Headaches
  4. Post-ictal
  5. Addison’s Disease (Adrenal Insufficiency)
    - Diagnosis: 8AM serum cortisol. If intermediate result, ACTH stimulation test

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21
Q

What are common causes for hyposmia/anosmia? List 11 causes.

A

Top 3 most common:
1. Trauma
2. URTI
3. Chronic Rhinosinusitis

Other:
1. Neurodegenerative disorders (e.g. Parkinson’s disease, Alzheimers)
2. Schizophrenia
3. Environmental toxins: Cadmium, Mercury, Formaldehyde, Zinc containing products (stop consuming these)
4. Sinonasal surgery
5. Nasal or intracranial tumors
6. Aging
7. Kallmann Syndrome
8. Foster-kennedy Syndrome

22
Q

What do you need to counsel patients about with anosmia? 5

A
  1. Ensure Smoke + Natural Gas detectors are present and work properly
  2. Change to electric stoves if possible
  3. Watch for expired foods
  4. Personal Hygiene (e.g. don’t fart in public, ensure to routinely shower)
  5. Monitor weight (possibly decreased eating)
23
Q

What are some possible causes dysosmia?

A
  1. Degenerative-regenerative process (post-trauma, URTI)
  2. Psychosis
  3. Aura-like hallucinations from central dysfunction
  4. Foul odours (purulence in CRS)
24
Q

What are causes of age-related changes in smell function? 3

A
  1. Cumulative damage to the olfactory receptors from repeated viral and other insults throughout life
  2. Ossification and closure of the foramina of the cribriform plate
  3. Development of early pathology associated with Alzheimer’s and Parkinson’s disease
25
Q

What are surgical treatment options for parosmia/phantosmia? 2

A
  1. Olfactory bulbectomy
  2. Endoscopic removal of olfactory neuroepithelium
26
Q

Discuss 10 different methods of olfactory testing/evaluation.

A

PSYCHOPHYSICAL TESTS
1. UPSIT
- University of Pennsylvania Smell Identification Test
- 4 booklets of 10 smells, must answer all (even if guessing)
- Scoring: 35/40 normal, 20-35 = Hyposmia; 10/40 = score by chance even if anosmia (6-19) total anosmia, ≤ 5/10 = malingering

  1. 1-minute smell test
    - Brief smell test
    - Abbreviated UPSIT, 12 items
  2. Sniffin’ Sticks
    - Uses n-butanol pen-like odor dispending device that contains different concentrations of odours
    - (1) Odor threshold: To test olfactory threshold - if none identified then move up on the stick concentration
    - (2) Odor discrimination: Can also be used for odorant discrimination (two sticks have the same scent and a third stick is different - smell 3 at a time)
    - (3) Odor identification: Can be used to identify different odours
  3. Butanol threshold test
    - Progressively increase the amount of butanol, until the subject can identify it 5 times in a row or fails to identify 4% butanol
  4. Odorant confusion matrix
    - Presents with 10 different odorants and repeat 10 times

Faster versions of UPSIT:
- Cross-Cultural Smell Identification test (CC-SIT): 12 micro-encapsulated odorants
- Pocket Smell Test (PST): 30 second 3-odour forced choice identification test

ELECTROPHYSIOLOGIC TESTING
1. Chemosensory EEG
- Uses Olfactory Event Related potentials (OERPs)
- Identifies brain EEG activity after odorant stimulus presentation
- Cannot localize site of lesion
- Used for research or medicolegal purposes only

  1. EOG: Electro-olfactography
    - Electrode in contact with olfactory neuroepithelium, identifies summated generator potentials of olfactory receptor neurons
    - Also used for research and medicolegal purposes
    - No local anesthesia - uncomfortable, sneezing, mucous
    - False positives in Kallman’s and Schizophrenia

ADJUNCTIVE TESTING
1. FNL
2. Neuro examination (CNs, MMSE - close associated with smell loss and dementia)
3. CT or MRI
4. Olfactory Biopsy

27
Q

What are 7 factors affecting olfactory testing?

A
  1. Age
  2. Satiety
  3. Gender (women have a better olfactory ability than men)
  4. Adaptation (usually occurs within 1-5 minutes, occurs at receptor cell level and centrally)
  5. Odour mixture
  6. Mental state (Neurologic state)
  7. Masking
28
Q

If a patient has objective anosmia, what is one medication you can try?

A

Short course of oral steroids.
Will help determine if this is contributed to by an inflammatory intranasal condition.

29
Q

What percentage of patients with Parkinson’s disease have smell dysfunction?

A

75-95%

30
Q

What other tests must you do if a patient presents with unilateral anosmia?

A

Ophthalmoscopy
- Rule out papilledema in the context of Foster-Kennedy Syndrome

31
Q

What is Foster-Kennedy Syndrome? What are the features of this syndrome? 5

A

What is it?
- Clinical syndrome associated with an anterior cranial fossa compressive mass/tumors of the olfactory groove or sphenoid ridge
- Results in ipsilateral optic nerve atrophy and increased ICP = papilledema
- Most commonly due to a meningioma of the ACF

Features:
1. Ipsilateral optic nerve atrophy
2. Central/Contralateral papilledema (because the ipsilateral nerve is atrophied; papilledema is from the increased ICP)
3. Ipsilateral anosmia/hyposmia
4. Headaches
5. Nausea/vomiting

32
Q

What is Kallman’s Syndrome?
What is the inheritance and gene?
What are the features
What is the treatment?

A

Kallman Syndrome
- Hypogonadotropic Hypogonadism
- Multiple causative genes
- Pediatric patients present with anosmia should be assessed for this as it will result in a delay in sexual development

Inheritance:
- X-linked (Xp22)
- Gene: ANOS1 –> Anosmin

Features:
1. Genito-urinary anomlies: Microphallus ± Cryptorchidism in males, Unilateral renal agenesis
2. Hearing loss
4. Agenesis of the olfactory bulbs (MRI)
5. Endocrine anomalies: Diabetes; Hypogonadotropic hypogonadism (deficiency of hypothalamic GnRH secretion)
6. Midline facial deformities

Treatment:
1. Referral to Endocrinology
2. Referral to Medical Genetics

33
Q

Which cranial nerves are most frequently damaged in head trauma (in order)?

A
  1. Olfactory nerve most common

I > VII > VIII > III/IV/VI

Vancouver says: I, VIII, X, VII, CI

34
Q

What is the difference between taste and flavour?

A

Flavour = Taste + Smell

35
Q

What are the 5 different tastes?

A
  1. Sweet
  2. Sour
  3. Salty
  4. Bitter
  5. Umami
36
Q

Define the following taste disorders:
1. Ageusia
2. Hypogeusia
3. Dysgeusia

A
  1. Ageusia: No taste
  2. Hypogeusia: Decreased taste
  3. Dysgeusia: Altered taste
37
Q

List a complete differential for altered taste sensation

A

A. POOR ORAL HYGIENE/INFECTION
1. Oral candidiasis
2. Periodontal disease
3. Gingivitis
4. Viral URTI
5. Xerostomia

B. ORAL APPLIANCES
1. Dentures
2. Obturators

C. IATROGENIC / TRAUMATIC
1. Chorda tympani injury
2. Post radiation
3. Head trauma

D. NUTRITIONAL
1. Malnutrition
2. Zinc or copper deficiency
3. B12 deficiency

E. MEDICATIONS
1. Intranasal zinc
2. Chlorhexidine (Peridex)
3. Chemotherapy
4. ACEI
5. ARBs
6. Dihydropyridine CCBs
7. Diuretics
8. Antibiotics - Macrolides, Terbinafine, FQs, Protease inhibitors, Griseofulvin, Pencillins, Tetracyclines, Nitromidazoles
9. Antiarrhythmics
10. Antithyroid agents
11. Antidepressants
12. Anticonvulsants
13. Lipid lowering agents

F. TOXINS
1. Pepper gas (oleoresin capsicum)
2. Weed killer with trifluralin
3. Ammonia
4. Benzene
5. Sulfuric acids
6. Cadmium
7. Acrylates
8. Iron
9. Lead
10. Chromium

G. CHRONIC MEDICAL CONDITIONS
1. Renal or hepatic failure
2. Cancer
3. HIV
4. Complicated Type 2 diabetes

38
Q

What is the difference between inhalant vs. irritant

A

Inhalants are not smelled
Irritants are smelled

39
Q

How do you tell someone with anosmia is malingering?

A

Total anosmia: A noxious stimulus (e.g. strong alcohol) should still stimulate a response because the trigeminal nerve is intact

If noxious stimulus fails to elicit a response –> likely malingering

UPSIT score < 6 (should still be able to get >6 right statistically)

40
Q

What are the chances of idiopathic anosmia based on age?

A
  • < 65% - 1%
  • 65-80 - 50%
  • > 80 - 75%
41
Q

What are the treatment options for anosmia? 4

A
  1. Safety considerations
  2. Nasal steroid
  3. Vitamin A and omega fatty acids have been shown to have some effect
  4. Olfactory training
42
Q

What is smell and olfactory training? Describe what is done in olfactory training?

A

Repeated short-term exposure to odours with the aim to improve general olfactory function.

  • In the “classical” approach, four essential oils - rose, eucalyptus, clove, and lemon are used
  • Patient sniff each one every day, BID x 10 seconds, for twelve weeks or longer
  • These four particular fragrances are used based on the theory of the “odour prism” which classifies smells as:
    1. Flowery (rose)
    2. Fruity (lemon)
    3. Spicy (cloves)
    4. Burnt
    5. Resinous (Eucalyptus)
  • This can be modified by changing the set of scents for 12 weeks at a time

Rhinology (11 decks)

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