Week 9- Taste & Smell

Question 1

What are chemoreceptors?

Answer 1

receptors that sense a change in ion concentration (increasing acidity)

Question 2

What are some chemoreceptors in the body?

Answer 2

Cutaneous nociceptors (chemicals on skin)

Lactic acid sensors in skeletal muscle

Gut enterocutes

Olfactory receptors (olfaction)

Taste busts (gustation)

Question 3

Where are taste bud found?

Answer 3

Found primarily on the upper surface of the tongue

Question 4

What makes a taste bud?

Answer 4

50 longe, spindle-shaped taste receptor cells together with supporting cells. Each has a taste pore

Question 5

What is the function of the lingual papillae?

Answer 5

to increase surface area and friction

Question 6

Name the 4 types of lingual papillae

Answer 6

• Filiform papilla
• Fungiform pailla
• Circumvallate papilla
• foliate pailla

Question 7

Describe the filiform papilla

Answer 7

• Most numerous
• do not contain tastebuds
• provide friction and grip
• gives tongue fury feel

Question 8

Describe fungiform papilla

Answer 8

• Contain 5 taste buds at the surface
• found on dorsal aspect of tongue
• Sweet, sour, bitter, umami
• VIIth CN innervation

Question 9

Circumvallate pailla, explain

Answer 9

• Dome shaped
• 8-12 in total
• contain 100 taste buds each
• glossopharyngeal innervation
• sensitive to bitter taste

Question 10

Foliate papilla, explain

Answer 10

• within folds at the side of tongue
• many taste buds
• IX Cn innervation

Question 11

Describe the life span of a taste bud

Answer 11

10-14 days
can be damaged by heat
- Surrounding epithelial cells differentiate into supporting cells (basal), then into receptor cells

Question 12

Describe taste receptor cells

Answer 12

• microvilli protrude slightly through the pore
• only stimulated by dissolved chemicals
• binding alters the cells ionic channels and depolarises cell- receptor potential
• RP initiates ATP or serotonin release, causing AP on primary gustatory neuron

Question 13

How does taste discrimination occur?

Answer 13

5 tastant receptors: Salty, sour, sweet, bitter, umami (and potentially starchy)

• different transduction channels for each tastant
• receptor cells respond to all, but are dominated by 1

Question 14

What are the different types of presynaptic cells?

Answer 14

Type 1: support cells
Type 3: depolarisation–> serotonin release
Type 2: G-protein coupled receptors resulting in ATP release
Type 4: basal cells

Question 15

What evokes bitter, sweet and umami taste?

Answer 15

Bitter: chemically diverse group of tastants, 50-100 receptors, each responding to a different bitter flavour

Sweet: glucose

Umami: amino acids

Question 16

What CNs synapse with taste buds in the mouth?

Answer 16

VII, IX, X

Question 17

Where do the nerves coming from the taste buds synapse

Answer 17

Gustatory cortex, via the brainstem and thalamus

Question 18

Where does the desire for taste originate?

Answer 18

Limbic system, adding affective dimensions to percept, along with the hypothalamus

Question 19

What other information influences taste perception?

Answer 19

• Olfaction
• temperature
• texture
• psychological factors

Question 20

What is the specific hunger phenomenon?

Answer 20

Craving a substance lacking in the body, i.e. lack salt appetite due to lack of Na in the body

Question 21

Where are olfactory chemoreceptors located?

Answer 21

In the olfactory mucosa at the roof of the nasal cavity

- olfactory receptors, supporting cells and basal cells

Question 22

What are basal cells precursors for and how often does this change occur?

Answer 22

Basal cells are precursors for olfactory receptor cells, being replaced every 2 months

Question 23

Describe the appearance of olfactory receptor cells

Answer 23

Enlarged distal end with several long cilia extending to the surface of the mucosa

Question 24

What do the cilia of olfactory receptor cells contain?

Answer 24

Odorant binding sites

• enter both naris
• must be volatile and water soluble

Question 25

Where do axons of the olfactory receptors form?

Answer 25

The olfactory nerve (CN I)

Question 26

Where do olfactory receptors synapse?

Answer 26

With peripheral dendrites of mitral cells in glomeruli, mitral neurons transmitting to the brainstem

Question 27

How do glomeruli play a role in scent perception?

Answer 27

Glomeruli only receive inputs from olfactory cells with the same odorant sensitivity

Question 28

How is olfactory stimulus detected?

Answer 28

By multiple olfactory receptors.

• Humans have more than 1000 different receptor types
• 1 odor molecule results in a unique receptor activation pattern, stimulating a unique glomeruli pattern

Question 29

Describe the central olfactory pathways

Answer 29

1. Subcortical route–> diffuse projections to limbic system –> primary olfactory cortex–> hypothalamic input, allowing close coordination between feeding, mating and direction orientation
2. Route through the thalamus to the orbitofrontal cortex–> conscious perception and discrimination of smell

Question 30

How are smell and emotion linked?

Answer 30

The subcortical route involves the amygdala, hippocampus and parts of the limbic system involved with emption and memory. Smell can also induce a strong sense of nostalgia.

Question 31

What is the Vomeronasal organ?

Answer 31

Detects pheromones, stimulating subconscious change in emotion and socio-sexual behaviour