Lecture 15 part 2: chemoreception Flashcards
4 types of chemoreceptors
- internal chemoreceptors
- free nerve endings in serous and mucous membranes
- olfactory receptors in nose (external)
- gustatory receptors on tongue (external)
olfaction
- sense of smell
- detects chemicals carried in air by food, predators, mates
gustation
sense of taste
- detection of chemicals emitted from ingested food
- easily distinguised for terrestrial animals, less so for aquatic
- uses diff transduction mechanisms from olfaction and processed in different integrating centers
olfaction pathway in vertebrates
olfactory epithelium-olfact bulb-cortex and limbic system
olfactory receptor cells (ORCs)
-can distinguish thousands of odorants
-located in roof of nasal cavity in olfactory epithelium
5-20 nonmotile cilia on end of dendrite to increase receptive surface area hundreds of times
coding-discriminating between odorants
- number of odors distinguished is large (>10000), but the number of genes coding odorant receptors is about 1000 (3% of genome), and each gene makes one receptor, and each olfactory neuron has ONE type of receptor protein
- that said, each odorant receptor can bind more than one odorant
- one odorant excites multiple neurons to different degrees, so coding is a unique combination of neurons excited differently
primates and cetaceans and smell
- humans have a third of their olfactory genes inoperable
- primates with coloured vision have fewer functional odorant receptor genes
- cetaceans (whales) do not smell, but have blowholes, despite all odorant genes being present, they just arn’t functional
detection of pheromones..
structurally and molecularly distinct from olfactory epithelium
location: nasal cavity in mammals and palate in reptiles
- receptor is linked to G-protein>activates phospholipase C
Transdunction of simulis for odors
-odorant causes conformational change, activating Gprotein
-G-protein detaches and moves to activate membrane adenylate cyclase
-adenylate cyclase converts ATP into cAMP
cAMP opens cAMP-gated ion channels
-Ca and Na enter the cell, causing a generator potential
Ca also opens Ca-activated Cl channels, causing Cl to leave, increasing depolarization
-generator potential opens voltage0gated Na channels, triggering APs
Taste buds
group of taste receptor cells on tongue, soft palate, larynx, and esophagus, some located externally for fish
taste receptor cells (TRC)
what taste buds are made of, are epithelial cells (not neurons) that release neurotransmitters
- their surface has microvilli to open the surface by pores
- each cell expresses more than one kind of taste receptor protein
- transmit signals through afferent neurons
discriminating tastes
- a single taste neuron may synapse with more than one TRC
- flavour from diff. tastes is a combination of input from taste buds, olfactory cells, and tactile receptors of mouth
transduction stimuli for salty foods is
Na+ influx into the cell, causing depolarization to open VG Ca channels, releasing neurotransmitters
transduction stimuli for sour foods is
H+ ions blocking K+ channels, resulting in depolarization and opening of Ca VG channels and release of neurotransmitters
transduction stimuli for sweet food
sweet molecule (glucose, fructose, etc) binds to receptor, causing conformational change, G-protein activating adenylate cyclase, which converts ATP into cAMP, activating protein kinase that phosphorylates and cloes a K channel, opening Ca channels and release of neurotransmitters
