Physiology Of Olfaction And Taste

Question 1

What are the three main types of cells in the olfactory epithelium

Answer 1

Olfactory cells
- site of signal transduction

Support cells
- act similar to astrocytes and microglia as well as produce mucous

Basal cells
- source of new receptor cells in case of damage or death

olfactory cells/neurons are one of a very select few neuron types that can easily regenerate

Question 2

Odorant binding proteins

Answer 2

Bind to the cillia of olfactory cells based on what order is present in the mucous
- help signal what smell/odor is to be signaled

Question 3

What is the function of mitral cells

Answer 3

Help carry electric signals out of the olfactory bulb into the olfactory tract
- similar to interneurons

Question 4

Olfactory transduction

Answer 4

1) odorant binding proteins bind specific odorant molecules.

2) olfactory binding proteins are bound to the olfactory receptors which are coupled to G(olf) G-proteins carrying cAMP
- once the olfactory binding proteins are bound to the receptors, cAMP is activated

3) cAMP causes opening of cation channels and beings to generate an action potential
- permeable to all three major cations (Na/K/Ca)

4) depolarization occurs
5) action potential is propagated along the olfactory nerve to the bulb

Question 5

What is the pathways for the mitral cells?

Answer 5

They travel to the following
1) anterior olfactory nucleus -> contralateral olfactory bulb

2) olfactory tubercle -> thalamus and frontal cortex
3) piriform cortex -> thalamus and frontal cortex
4) amygdala -> hypothalamus/thalamus and frontal cortex
5) entorhinal cortex -> hippocampus

Question 6

What mitral cell pathways make up emotional responses to odors?

Answer 6

Amygdala pathway

- specifically the part that travel to the hypothalamus

Question 7

What mitral cell pathways make up memory responses to odors?

Answer 7

Entorhinal cortex

- specifically the pathway which travels to the hippocampus

Question 8

What mitral cell pathways make up discrimination responses to odors?

Answer 8

All 5 except for anterior olfactory nucleus

- any pathway that communicates in some way with the orbitofrontal and frontal cortex

Question 9

What aspect of the thalamus is olfactory information passed through?

Answer 9

Dorsomedial aspect of the thalamus

note not all pathways travel through the thalamus

Question 10

Vomeronasal organ

Answer 10

An olfactory organ that is responsible for reacting to pheromones
- travels through amygdala -> hypothalamus

Question 11

Anosmia

Answer 11

Inability to smell

Can be congenital but rare

Is one of the earliest signs of Alzheimer’s disease

Is so closely tied together with taste that often hypoguesia (weakened taste sensations) are present as well.

Question 12

Hyperosmia

Answer 12

Enhanced smelling

Rare but can be seen in pregnant women

Question 13

Types of taste buds (papillae)

Answer 13

Folate

Circumvallate

Fungiform

Question 14

Reminder of what 3 cranial nerves are associated with taste

Answer 14

Facial nerve = 2/3 anterior via chordae tympani

Glossopharyngeal nerve = 1/3 posterior

Vagus nerve = taste buds in the oropharynx

note the somatic sensations are the same except facial nerve is replaced by mandibular division of trigeminal nerve

Question 15

What are the 5 primary taste qualities

Answer 15

Bitter

Salty

Sour

Sweet

Umami (savory)

Question 16

How is bitter taste transduction work

Answer 16

Bitter = quinine and alkaloid derivatives

1) bitter molecules bind to G-protein coupled membrane receptors in the taste bud
2) phosphlipase C then increases IP3 and Ca levels which opens TRP channels
3) TRP channels then cause depolarization
* bitter taste is the strongest of all tastes since it is the most important for survival*

Question 17

How does sweet taste transduction work?

Answer 17

Similar to bitter just sucrose is now the molecule

Question 18

How does umami taste transduction work?

Answer 18

Similar to bitter and sweet except glutamate is now the molecule

Question 19

How does the taste of sour transduction work?

Answer 19

1) H+ ions enter the membrane of taste buds via sodium channels (ENaC)
2) causes direct depolarization immediately

Question 20

How does salty taste transduction work?

Answer 20

Similar to sour except uses direct sodium ions instead of protons

Question 21

What neurotransmitters are used in taste?

Answer 21

ATP and serotonin

Question 22

The general gestation pathways

Answer 22

1) anterior 2/3 of tongue
- travels to geniculate ganglion -> nucleus of solitary tract -> VPM nucleus of the thalamus -> gustatory cortex

2) posterior 1/3 of tongue
- travels to petrosal ganglion -> gustatory area of the solitary tract -> VPM nucleus of the thalamus -> gustatory cortex

3) oropharynx
- travels to nodose ganglion -> gustatory area of the solitary tract -> VPM nucleus of the thalamus -> gustatory cortex