physiology of taste and smell

Question 1

where do the majority of tastebuds sit?

Answer 1

the papillae in the tongue

Question 2

what are the 4 types of papillae?

Answer 2

filliform (do not contain taste buds)
fungiform
vallate
foliate
(all 3 contain taste buds)

Question 3

how is taste produced?

Answer 3

Binding of taste provoking chemical (tastant) to receptor cells produces depolarising receptor potential

Receptor potential initiates action potentials in afferent nerve fibres which synapse with receptor cells

Signals conveyed by cranial nerves via brainstem and thalamus to cortical gustatory areas

Question 4

what are the 3 abnormalities of taste?

Answer 4

ageusia (loss of taste function)
hypogeusia (reduced taste function)
dysgeusia (distortion of taste function)

Question 5

what can cause ageusia?

Answer 5

nerve damage
local inflammation
some endocrine disorders

Question 6

what can cause hypogeusia?

Answer 6

chemotherapy & medications

Question 7

what can cause dysgeusia?

Answer 7

glossitis
gum infections
tooth decay
reflux
upper respiratory infections
medications
neoplasms
chemotherapy
zinc deficiency

Question 8

what are the 4 neural systems of the nose?

Answer 8

main olfactory system (CN I)
trigeminal somatosensory system (CN V)
accessory olfactory system
nervus terminalis (CN 0)

Question 9

what smells does CN I mediate?

Answer 9

common odours e.g. roses

Question 10

what role does CN V play in smell?

Answer 10

CN V has a chemical and non-chemical stimulus (irritation, burning, cooling, tickling).

it is protective- if you sniff something harmful it will help to halt inhalation to protect the lungs.

Question 11

what happens before neural conduction from olfactory cleft to the brain?

Answer 11

odour must enter the nose and pass into olfactory cleft and turn from air to liquid

Question 12

describe olfactory receptors

Answer 12

• Specialised endings of renewable afferent neurons
• Olfactory receptors have a life span of about 2 months
• Axons of olfactory receptors collectively form afferent fibres of olfactory nerve
• 6 million receptor cell axons coalesce into 30-50 fasicles

Question 13

what are the abnormalities of smell?

Answer 13

Anosmia (inability to smell)

Hyposmia (reduced ability to smell)

Dysosmia (altered sense of smell)

Phantosmia (smell perceived in the absence of stimulus (olfactory hallucination)

Question 14

what is the difference between conductive and sensorineural smelling loss?

Answer 14

In conductive losses, pathology blocks inspired odorants from reaching the olfactory cleft in the nasal cavity.
In sensorineural losses, the dysfunction is attributed to the olfactory receptor neurons or their central projections.

Question 15

what are causes of conductive abnormalities in smell?

Answer 15

Nasal polyps
Rhinitis
Nasal mass

Question 16

what are causes of sensorineural abnormalities of smell?

Answer 16

Viral (normally common cold, now COVID)
Head trauma
Neurological conditions e.g. parkinsons, alzheimers
Brain tumours
Medications