Chemosenses 1

Question 1

sweet molecule

Answer 1

Sugar molecules or artificial sweeteners

Question 2

sour molecule

Answer 2

H+ (from acids)

Question 3

bitter molecule

Answer 3

Quinine, caffeine, some poisons

Question 4

salty molecule

Answer 4

Na+

Question 5

umami molecule

Answer 5

Amino acids etc.

Question 6

sweet method of transduction

Answer 6

G-protein coupled receptor (large molecule)

Question 7

sour method of transduction

Answer 7

Diffusion through amiloride sensitive Na+ channel or blocking K+ channel

Question 8

bitter method of transduction

Answer 8

G-protein coupled receptor (large molecule)

Question 9

salty method of transduction

Answer 9

Diffusion through amiloride sensitive Na+ channel

Question 10

umami method of transduction

Answer 10

G-protein coupled receptor (large molecule)

Question 11

central taste pathways

Answer 11

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.

Question 12

central taste pathways continued

Answer 12

Secondary pathways from the medulla triggers the Parasympathetic NS
Reflexes for salivation, production of gastric juices, gagging, vomiting

Question 13

localized lesions within the thalamus or gustatory cortex from head injuries, chemicals or medications, radiation for cancer treatment

Answer 13

Ageusia- the loss of taste perception

Question 14

localized lesions within the hypothalamus or amygdala

Answer 14

Chronic overeating
Ignore food totally
Alters food preferences and motivation to eat (remember the four F’s)

Question 15

The perception of flavor is created by

Answer 15

the neural pathways in the brain.

Question 16

labeled line hypothesis

Answer 16

Individual taste receptor cells for each stimulus – Does NOT happen because not enough types of receptor cells!

Question 17

in reality (labeled line hypothesis rebuttal)

Answer 17

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

Question 18

population coding

Answer 18

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:

Question 19

why is smell important

Answer 19

Combines with taste to help identify food (80% of taste from smell)
Warns of harmful substances or places
Mode of Communication = Pheromones

Question 20

pheromones

Answer 20

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

Question 21

vomeronasal cavity

Answer 21

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

Question 22

olfactory epithelium

Answer 22

small thin sheet of cells high up in the nasal cavity

Question 23

olfactory receptor cells

Answer 23

site of transduction; are bipolar neurons (unlike taste receptors) continually grow, die, regenerate (30-60 day cycle) throughout life

Question 24

supporting cells

Answer 24

similar to glia provide metabolic and physical support; help in production of mucus

Question 25

basal cells

Answer 25

stem cells that produce new receptor cells

Question 26

odorants

Answer 26

the chemical stimuli for olfaction; dissolve in mucus before they reach receptor cells

Question 27

mucus in olfactory epithelium

Answer 27

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

Question 28

things in mucus layer

Answer 28

Odorant-binding proteins – help concentrate odorants and shuttle them to receptors
Antibodies – protect brain from exposure to viruses and bacteria

Question 29

why humans are worse smellers than dogs

Answer 29

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

Question 30

olfactory nerve

Answer 30

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

Question 31

cribriform plate

Answer 31

A thin sheet of bone with holes through which small clusters of axons penetrate, travelling to the Olfactory bulb

Question 32

anosmia

Answer 32

Inability to smell, can be due to the severing of the olfactory nerves from a blow to the head

Question 33

Olfactory Receptor Neurons

Answer 33

Olfactory Transduction-G-protein-coupled receptors

Question 34

mechanisms of olfactory transduction

Answer 34

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.

Question 35

taste vs smell signaling pathways

Answer 35

Taste- Need Ca++ to release neurotransmitter

Smell- Need membrane depolarization to cause action potential