Lecture 35 - Taste and Olfaction

Question 1

Olfaction works via the following pathway:

Olfactory ______ receives chemical input via airborne odorants –> transmits signal via Olfactory Receptor Neurons to olfactory _____ –> communicates with ______ cortext (main olfactory cortex) + Amygdala (emotional response) + Olfactory Tubercle + Entorhinal Cortex –> these communicate with _____ cortext + Thalamus + Hypothalamus + Hippocampus

Answer 1

Olfactory Epithelium

Olfactor Bulb

Pyriform cortex (main olfactory cortex)

Orbitofrontal cortex

Question 2

Olfactory epithelium is comprised of Olfactory Receptor Neurons (ORNs) that have ______ with many different receptors for odorants, _________ cells that are adjacent to/support ORNs and detoxify chemicals in the epithelium, ______ mucus glands, and ______ cells (which are true stem cells that continuously divide and form new ORNs).

Keep in mind ORNs project _______ axons (myelinated or unmyelinated?) through the _____ plate and synapse with the dendrites of the Olfactory buld in _______ (what kind of structure?).

Answer 2

Cilia

Sustentacular cells

Bwoman’s mucus glands

Basal

Unmyelinated axons

Cribiform plate
Glomeruli

Question 3

The olfactory bulb is comprised of 2 cells types:

1. ______ cells, which project along the ______ Olfactory tract to the Piriform cortex.
2. ______ cells which project along the ______ Olfactory tract to the _______ Olfactory Nucleus.

Keep in mind ORNs each have a SPECIFIC receptor type that responds with varying levels of Sensitivity and Selectivity to DIFFERENT Odorants, and they follow a “birds of a feather” rule: same odorant receptors –> project to same _____ in the Olfactory bulb.

Answer 3

Mitral cells

Lateral Olfactory Tract (LOT)

Tufted cells

Medial Olfactory Tract (MOT)

Anterior Olfactory Nucleus

Glomerulus

Question 4

Interestingly, the Olfactory tracts do not ______, and unlike other sensory tracts, the Cortical connections occur BEFORE ______ connnections.

Answer 4

Decussate

Thalamic (usually a relay station for sensory info on its way to the cortex, but NOT in the case of olfaction.)

Question 5

There are ______ neurons in the Olfactory bulb, and these are among the first to go in Parkinson’s disease. This is a good mode for early detection of Parkinson’s, and it is a good way to differentiate between Parkinson’s and Parkinsonism.

Answer 5

Dopaminergic neurons

Question 6

ORNs take about ____ months to regenerate, so it should make sense that if someone loses smell due to ORN damage, they may start to regain smell in a few months.

Keep in mind _____ has been shown to reduce severity and duration of some viral infections, BUT it is toxic to the nasal epithelium, causing permanent damage.

Answer 6

2 months

Zinc

Question 7

Cranial nerves ___ + ___ + ___ innervate taste buds. Which areas are innervated by each of these CNs?

Answer 7

VII + IX + X

CN VII –> Anterior 2/3 of tongue

CN IX –> Posterior 1/3 of tongue

CN X –> Epiglottis

Question 8

There are 3 types of taste bud papilae.

1. _______ papilae which are on the anterior 2/3 of the tongue (so CN ____)
2. _______ papilae on the edges of of the tongue
3. _______ papilae on the posterior 1/3 of the tongue (so CN _____)

Which has the most taste buds per papila?

Answer 8

1. Fungiform

CN VII

2. Foliate
3. Circumvalate

CN IX

Circumvalate, with about 250 buds/papila (the others have about 10 per)

Question 9

Taste buds are composed of a Taste pore through which dissolved Tastants enter and are received by tens of taste cells (specialized ______ cells) that synapse with gustatory neurons from CNs VII, IX, or X –> gustatory signal travels to Nucleus of _______ tract.

Answer 9

Epithelial cells

Nucleus of Solitary Tract

Question 10

Taste cells each have _____ (how many?) type(s) of receptor(s) –> they respond to either sweet, salty, sour, umami, or bitter. Keep in mind adjacent taste cells can have a different composition of receptors.

Salt and Sour receptors are ligand-gated _____ channels, while Sweet, Umami, and Bitter receptors are G-protein coupled receptors that activate ______ channels.

Answer 10

One

Ion channels

TRPM5 channels

Question 11

_____ _____ and Greater Superior ______ branches of the facial nerve (CN VII) are the afferents for the anterior 2/3 of the tongue. The ______ branch of the Glossopharyngeal nerve (CN IX) is the afferent for the posterior 1/3 of the tongue.

Answer 11

Chorda Tympani

Greater Superior Petrosal

Lingual

Question 12

Gustatory sensory information is conveyed in the following order:

First, taste cells bind tastants –> convey signal to gustatory neurons of CNs VII + IX + X –> project to Nucleus of ______ tract –> project to _____ and Thalamus –> project to ______ cortex (more so the right than the left).

Answer 12

Nucleus of Solitary Tract

VPM and Thalamus

Insular cortex (main gustatory cortex)

Question 13

Though primary gustatory defects are possible, up to 80% of taste defects result from _______ issues.

Answer 13

Olfactory

Question 14

Some gustatory fuctions/dysfunctions are hereditary. The ability to taste PTU (which is bitter) is autosomal _____.

____-_____ syndrome (Type I Familial Autonomia) results in severe Hypogeusia or Ageusia from lack of taste bud development.

Answer 14

Dominant

Riley-Day