Chemosenses 1 Flashcards
sweet molecule
Sugar molecules or artificial sweeteners
sour molecule
H+ (from acids)
bitter molecule
Quinine, caffeine, some poisons
salty molecule
Na+
umami molecule
Amino acids etc.
sweet method of transduction
G-protein coupled receptor (large molecule)
sour method of transduction
Diffusion through amiloride sensitive Na+ channel or blocking K+ channel
bitter method of transduction
G-protein coupled receptor (large molecule)
salty method of transduction
Diffusion through amiloride sensitive Na+ channel
umami method of transduction
G-protein coupled receptor (large molecule)
central taste pathways
Taste receptors on the tongue signal
Gustatory axons which travel along 3 cranial nerves then signal
Gustatory nucleus of the medulla which signals
Ventral Posterior Medial (VPM) nucleus of the thalamus which signals
Primary gustatory cortex (within the cerebral cortex) for the conscious experience of taste.
central taste pathways continued
Secondary pathways from the medulla triggers the Parasympathetic NS
Reflexes for salivation, production of gastric juices, gagging, vomiting
localized lesions within the thalamus or gustatory cortex from head injuries, chemicals or medications, radiation for cancer treatment
Ageusia- the loss of taste perception
localized lesions within the hypothalamus or amygdala
Chronic overeating
Ignore food totally
Alters food preferences and motivation to eat (remember the four F’s)
The perception of flavor is created by
the neural pathways in the brain.
labeled line hypothesis
Individual taste receptor cells for each stimulus – Does NOT happen because not enough types of receptor cells!
in reality (labeled line hypothesis rebuttal)
In reality, neurons broadly tuned, become less specific:
One neuron can be triggered for both salt and sour tastes
Several taste receptor cells can converge onto one gustatory afferent axon
Many axons from different taste neurons and from different papillae can converge along the pathway to the gustatory cortex
population coding
Deciphering taste from a large number of broadly tuned neurons. What combinations of neurons are firing? How sensitive are each of these neurons to that stimulus? Which subset is firing strongly, moderately, or not at all? How many of each? Leads to different overall firing rate patterns that are interpreted by the brain for specific Flavor.
Also signals from other receptors that through population coding the brain turns all of the stimuli into one concrete flavor:
why is smell important
Combines with taste to help identify food (80% of taste from smell)
Warns of harmful substances or places
Mode of Communication = Pheromones
pheromones
chemicals released by the body Accessory Olfactory System – detects pheromones and mediates behaviors Important signals Reproductive behavior Territorial boundaries Identification of Individuals Aggression or Submission
vomeronasal cavity
Consists of a separate chemically sensitive region in the nasal cavity
Vomeronasal cavity projects to the olfactory bulb and then to the hypothalamus
In other animals, used to detect pheromones which mediate behaviors having to do with mother nurturing offspring, mating, territorial behaviors, and finding food.
Present in Human Adults
olfactory epithelium
small thin sheet of cells high up in the nasal cavity
olfactory receptor cells
site of transduction; are bipolar neurons (unlike taste receptors) continually grow, die, regenerate (30-60 day cycle) throughout life
supporting cells
similar to glia provide metabolic and physical support; help in production of mucus
basal cells
stem cells that produce new receptor cells
odorants
the chemical stimuli for olfaction; dissolve in mucus before they reach receptor cells
mucus in olfactory epithelium
The olfactory epithelium exudes a thin coating of mucus which flows constantly and is replaced about every 10 minutes.
This mucus layer is water based with dissolved mucopolysaccharides (long sugar chains), proteins (including antibodies), enzymes, odorant-binding proteins, and salts
things in mucus layer
Odorant-binding proteins – help concentrate odorants and shuttle them to receptors
Antibodies – protect brain from exposure to viruses and bacteria
why humans are worse smellers than dogs
Due to small surface area of olfactory epithelium
Humans 10 cm2 vs. Dogs 170 cm2 (100,000x better sense of smell)
Fewer number of olfactory receptor cells
Dogs 100x more per cm2 in the Olfactory recess
Dogs sniff 5 times per second
Dogs can even tell which nostril detected the smell
olfactory nerve
Odorants activate transduction processes in olfactory receptor cells (neurons)
Axons of olfactory receptor cells form clusters (filaments of the olfactory nerve) and pass through holes in the cribriform plate, constituting an Olfactory nerve
cribriform plate
A thin sheet of bone with holes through which small clusters of axons penetrate, travelling to the Olfactory bulb
anosmia
Inability to smell, can be due to the severing of the olfactory nerves from a blow to the head
Olfactory Receptor Neurons
Olfactory Transduction-G-protein-coupled receptors
mechanisms of olfactory transduction
Olfactory Transduction is initiated by volatile odorants binding to G-protein-coupled receptors on Cilia (nonmotile) of olfactory receptor cells.
G protein moves to enzyme Adenylyl Cyclase activating it
Adenylyl cyclase produces cyclic AMP (cAMP)
cAMP binds to cation-selective cAMP-gated channels causing them to open
Na+ and Ca2+ (mostly Ca2+) flow into the cell depolarizing the cell.
Ca2+ binds to Ca2+-activated chloride channels causing them to open and Cl- flows out amplifying the depolarization
Cl- current outward depolarizes the cell (due to high levels of Cl- inside the cell, normally hyperpolarizes)
If threshold is reached at the axon hillock, an action potential will be transmitted to the olfactory bulb.
taste vs smell signaling pathways
Taste- Need Ca++ to release neurotransmitter
Smell- Need membrane depolarization to cause action potential
