Taste and olfaction

Question 1

What is the contribution of the trigeminal nerve (V) in the mouth?

Answer 1

• general sensation and common chemical sense of anterior 2/3 of tongue
• soft palate

Question 2

What is the contribution of the glossopharyngeal nerve (IX) in the mouth?

Answer 2

• general sensation and chemical sense of posterior 1/3 of tongue
• oropharynx

Question 3

What is the contribution of the facial nerve in the mouth?

Answer 3

• soft palate

Question 4

What is the contribution of the vagus nerve in the mouth?

Answer 4

• oropharynx

Question 5

List the different types of papillae

Answer 5

• vallate
• fungiform
• foliate
• filiform

Question 6

Vallate papillae

Answer 6

• V-shaped row at back of tongue

* each house 100-300 taste buds

Question 7

Fungiform papillae

Answer 7

• scattered over tongue

* each house 5 taste buds

Question 8

Foliate papillae

Answer 8

• found in small trenches on side of tongue
• each has 100-150 taste buds
• most degenerate in early childhood

Question 9

Filiform papillae

Answer 9

• tactile receptors

* no taste buds

Question 10

Why are there taste buds on palate and pharynx?

Answer 10

probably for reflex responses (gagging or vomiting)

Question 11

What is a taste bud?

Answer 11

made of 3 types of epithelial cells:
• supporting cells
• gustatory receptor cells
• basal cells

• 50 gustatory cells per taste bud
• each has a gustatory hair that projects through taste pore

Question 12

What are the types of taste?

Answer 12

• sour
• sweet
• bitter
• salty
• astringent
• pungent
• umami

Question 13

How does the perception of flavour happen? What is involved?

Answer 13

• direct chemical stimulation of taste buds -> gustatory cortex
• stimulation of somatosensory receptors by vapours -> olfactory cortex
• stimulation of somatosensory receptors in the oral and nasal cavities -> CNV and CNIX to somatosensory cortex: respond to pungency, spices, temperature, texture
• vision -> visual cortex

Question 14

Where is the primary olfactory area?

Answer 14

anterior insula / frontal operculum

Question 15

Describe the olfactory epithelium

Answer 15

• 2cm2 yellowish patch in roof of nasal cavity
• contains 10 million to 100 million receptors
• olfactory receptor
• Bowmans gland (mucus)
• supporting cells (nourish)
• basal cells (replace receptor) average lifespan 30-60 days
• axons thin, unmyelinated, gather into 20 bundles, olfactory fila (pass through cribriform plate)

Question 16

Describe the olfactory receptor

Answer 16

• bipolar neuron with 10-30 immobile cilia (olfactory hairs emerging from the dendrite
• responds to chemical stimulation of odourant molecule

Question 17

Describe the olfactory tract

Answer 17

• from bulb, projects directly to ipsilateral primary olfactory cortex in temporal lobe (entorhinal cortex, piriform cortex, amygdala) -> limbic structures and hypothalamus (emotional and motivational responses to smell, behavioural and psychological responses to odours)

Question 18

Primary olfactory cortex

Answer 18

conscious awareness of odour

Question 19

Where in the amygdala does the smell go?

Answer 19

Rhinencephalon
• bulb
• tract
• striae
• anterior perforated substance
• primary olfactory cortex (entorhinal cortex, piriform, parts of amygdala)

Question 20

What is unique about the olfaction pathway?

Answer 20

• sensory receptor is bipolar neuron (as opposed to special sensory)
• does not go through thalamus or brainstem
• direct short route to primary olfactory cortex with connections to limbic system and other parts of brain

Question 21

What is anosmia

Answer 21

• loss of the sense of smell, either total or partial
• conductive problems (nasal polyps, septal deviation, inflammation)
• sensorineural (head injury, Parkinson’s or Alzheimer’s disease)