Week 9- Taste & Smell Flashcards
What are chemoreceptors?
receptors that sense a change in ion concentration (increasing acidity)
What are some chemoreceptors in the body?
Cutaneous nociceptors (chemicals on skin)
Lactic acid sensors in skeletal muscle
Gut enterocutes
Olfactory receptors (olfaction)
Taste busts (gustation)
Where are taste bud found?
Found primarily on the upper surface of the tongue
What makes a taste bud?
50 longe, spindle-shaped taste receptor cells together with supporting cells. Each has a taste pore
What is the function of the lingual papillae?
to increase surface area and friction
Name the 4 types of lingual papillae
- Filiform papilla
- Fungiform pailla
- Circumvallate papilla
- foliate pailla
Describe the filiform papilla
- Most numerous
- do not contain tastebuds
- provide friction and grip
- gives tongue fury feel
Describe fungiform papilla
- Contain 5 taste buds at the surface
- found on dorsal aspect of tongue
- Sweet, sour, bitter, umami
- VIIth CN innervation
Circumvallate pailla, explain
- Dome shaped
- 8-12 in total
- contain 100 taste buds each
- glossopharyngeal innervation
- sensitive to bitter taste
Foliate papilla, explain
- within folds at the side of tongue
- many taste buds
- IX Cn innervation
Describe the life span of a taste bud
10-14 days
can be damaged by heat
- Surrounding epithelial cells differentiate into supporting cells (basal), then into receptor cells
Describe taste receptor cells
- 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
How does taste discrimination occur?
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
What are the different types of presynaptic cells?
Type 1: support cells
Type 3: depolarisation–> serotonin release
Type 2: G-protein coupled receptors resulting in ATP release
Type 4: basal cells
What evokes bitter, sweet and umami taste?
Bitter: chemically diverse group of tastants, 50-100 receptors, each responding to a different bitter flavour
Sweet: glucose
Umami: amino acids
What CNs synapse with taste buds in the mouth?
VII, IX, X
Where do the nerves coming from the taste buds synapse
Gustatory cortex, via the brainstem and thalamus
Where does the desire for taste originate?
Limbic system, adding affective dimensions to percept, along with the hypothalamus
What other information influences taste perception?
- Olfaction
- temperature
- texture
- psychological factors
What is the specific hunger phenomenon?
Craving a substance lacking in the body, i.e. lack salt appetite due to lack of Na in the body
Where are olfactory chemoreceptors located?
In the olfactory mucosa at the roof of the nasal cavity
- olfactory receptors, supporting cells and basal cells
What are basal cells precursors for and how often does this change occur?
Basal cells are precursors for olfactory receptor cells, being replaced every 2 months
Describe the appearance of olfactory receptor cells
Enlarged distal end with several long cilia extending to the surface of the mucosa
What do the cilia of olfactory receptor cells contain?
Odorant binding sites
- enter both naris
- must be volatile and water soluble
Where do axons of the olfactory receptors form?
The olfactory nerve (CN I)
Where do olfactory receptors synapse?
With peripheral dendrites of mitral cells in glomeruli, mitral neurons transmitting to the brainstem
How do glomeruli play a role in scent perception?
Glomeruli only receive inputs from olfactory cells with the same odorant sensitivity
How is olfactory stimulus detected?
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
Describe the central olfactory pathways
- Subcortical route–> diffuse projections to limbic system –> primary olfactory cortex–> hypothalamic input, allowing close coordination between feeding, mating and direction orientation
- Route through the thalamus to the orbitofrontal cortex–> conscious perception and discrimination of smell
How are smell and emotion linked?
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.
What is the Vomeronasal organ?
Detects pheromones, stimulating subconscious change in emotion and socio-sexual behaviour
