Chemical senses Flashcards
What is the use of olfaction?
Olfaction is the oldest evolutionary system Avoiding danger (smoke of fire) Eating Parenting Social (pheromones)
What is chemotaxis?
Chemotaxis is the oldest sense: sensing the presence of sugar crystal.
Bacteria can sense their environment by detecting chemical cues
What are chemicals that humans can smell?
odorants
How do we ‘catch’ odorants?
Filtering of air through hairs and cavities in the nose
Where do olfactory sensory neurons lie?
Olfactory sensory neurons in the nose are imbedded in olfactory epithelium
What is the life-span of olfactory neurons?
Olfactory neurons are short-lived (30-60 days) and are replaced by the basal stem cell population
How is the human olfactory system organized?
Olfactory receptors –olfactory nerve (I)–> Olfactory bulb —olfactory tract–> olfactory bulb targets [pyriform cortex, olfactory tubercle, amygdala, entorhinal cortex]
Animals vs humans
Animals have an increased number of olfactory receptor
neurons and increased olfactory epithelium.
Yet though we do not use olfaction as a major source of spatial information we are still able to trace objects in space. We have a sensitive olfactory detection – ozon at 10 molecules per billion in room air
How do we recognize 10000 different
odours?
Discovery of a large family of genes for olfactory
receptors: 1000 genes (3% of all genes).
Individual olfactory sensory neurons can
respond to different odorants
How are different odorant receptor type localized?
Each odorant receptor type is localized in one of four zones in the olfactory epithelium (of the mouse) Each odorant receptor gene is expressed in only about 0.1% of olfactory sensory neurons, suggesting that each neuron expresses only one type of odorant receptor. Neurons with the same receptors are all located in one zone but are scattered throughout that zone along with neurons expressing other receptors
Where do olfactory cells project to?
Olfactory cells project axons to glomeruli in the olfactory bulb.
Same receptor, same glomerulus:
one glomerulus (20-50 neurons) receives signal from
several thousand olfactory neurons
What is the function of granule cells?
Granule cells provide a curtain of inhibition and increase signal-to-noise ratio.
Where is olfactory information processed?
Olfactory information is processed in several regions of the cerebral cortex. (Piriform cortex)
What are pheromones?
Pheromones: a chemical substance produced and released into the environment by an animal, affecting the behavior or physiology of others of its species.
Do we also have pheromones?
Human hypothalamus responds to inhalation of hormones.
Exposure to androgen and estrogen-like compounds at concentrations below the level of conscious detection can elicit both behavioral responses and different patterns of brain activation
By what is taste influenced?
Taste is influenced by smell.
Where are taste buds located?
Taste buds are located in three types of papillae on the human tongue.
Which three types of papillae on the human tongue exist?
Circumvallate
Foliate
Fungiform
SOUR
What is the meaning of different tastes? What molecule is sensed?
fresh? H+
BITTER
What is the meaning of different tastes? What molecule is sensed?
poisonous?
SALT
What is the meaning of different tastes? What molecule is sensed?
NaCl
SWEET
What is the meaning of different tastes? What molecule is sensed?
energy, sugars
UMAMI
What is the meaning of different tastes? What molecule is sensed?
proteins, amino acids
Sensory transduction: Salt and acid
through ion channels.
Salt: Na+ channel
Acids: H+ channel
