The Chemical Senses Flashcards
Main Chemical senses
- Taste
- Smell
- Co2/O2 levels
- Chemical irritants
- Acidity
What do chemoreceptors do?
Chemoreceptors in the arteries of the neck measure Co2 and O2 levels in the blood
How are chemical irritants detected?
Nerve endings in skin/mucous membranes warn us of chemical irritants
How is acidity detected?
Sensory nerve endings in muscle respond to acidity - burning feeling that comes with exercise and O2 debt.
How has taste sense evolved?
Thought that humans innately enjoy sweet flavours and avoid bitter tastes. However, experience can strongly modify our innate preferences
Five basic tastes
- Sweet
- Bitter
- Sour
- Salt
- Umani
What is the umani taste?
The taste of monosodium glutamate
How is ‘flavour’ perceived?
The combination and quantities of the five tastes as well as the texture, temperature and smell of food.
Main organ of taste
Tongue
Other secondary body regions responsible for taste
Palate - roof of mouth containing taste buds that detect flavour
Epiglottis - taste buds present
Pharynx and Nasal Cavity - Odours pass through the pharynx and detected by olfactory receptors in the nasal cavity
Parts of the tongue with specific taste receptors
Front of the tongue - sweet Front sides - Salty Back sides - Acid Back - Bitter All areas of the tongue can detect all tastes just at slightly lower levels.
What are the papillae?
- Fungiform papillae: mushroom shaped
- Folate papillae: ridge shaped
- Vallate papillae: pimple shaped
Structure of the papillae
Contain taste buds embedded into them. In the taste buds is the taste pore that is the chemically sensitive end of the taste bud. Also contains, taste cells which connect and synapse with the gustatory afferent axons that transmit taste information to the brain
Which cells transmit taste information to the brain?
The gustatory afferent axons
What are taste receptors and how were they investigated?
Taste receptors are the cells that respond primarily (or even exclusively) to one of the five basic tastes.
Experiment:
- Each taste cell attached to a microelectrode.
- The taste bud is sequentially exposed to salt (NaCl), bitter, sour and sweet stimuli then the membrane potential recorded.
- The taste receptor cells display different sensitivities.
- Taste receptor cells form synapses with gustatory different axons to transmit this gustatory information. Once the stimulus binds to the taste receptor, there is a firing of action potentials.
Which tastes have ion channel mechanisms?
Saltiness and Sourness both have ion channel mechanisms
What is the taste transduction mechanism for saltiness?
- Na+ passes through the sodium selective channels (amiloride sensitive channels), down its concentration gradient
- Depolarises the taste cells due to the influx of sodium as more positive ions into the cell activating the VGSCs and also activating the VGCCs.
- This causes the release of vesicular neurotransmitters which fuse with the cell membrane and are released by exocytosis. They contain gustatory afferents that transmit the signal to the brain.
What triggers the saltiness transduction mechanism?
It is triggered by the influx of sodium ions into a special Na+ selective channel called the amiloride sensitive channel.