Olfaction And Taste

Question 1

Receptor organ for olphaction

Answer 1

Olfactory epithelium

Question 2

Olfactory epithelium - cell types

Answer 2

Olfactory neurons -> olfactory cilia, receptors, knob, “fila”, form I CN

Supporting cells -> around neurons, secrete mucus (also by Bowman’s glands)

Regenerative cells -> replace olfactory neurons (30-45 days), have cilia

Question 3

Why do we have mucus layer?

Answer 3

Odorant substances need to dissolve in order to be recognized

Question 4

Input pathway

Answer 4

Axons of olfactory neurons enter small grooves -> cross cribriform plate of ethmoid bone -> olfactory bulb: synapse -> input to brain through olfactory tract

Question 5

Olfactory system receptor

Answer 5

Proper neuron

Question 6

Olfactory transduction

Answer 6

Odorant substance contacts GP receptor on olfactory neurons
Activation G prot = release 2nd messengers (cAMP or IP3)= opening of cation channels —> Na+ enters the cell = depolarizing neurons -> AP to next neuron

Question 7

How many different olfactory receptors do we have?

Answer 7

Unknown, only 1 receptor type per neuron

Question 8

Organization of olfactory bulb

Answer 8

Fibres (input) reach the periphery of the olfactory bulb
Processing from periphery to centre
Output of the bulb exits from the centre

Question 9

Olfactory cortex

Answer 9

Main areas
- anterior olfactory nucleus (many bilateral connections)
- olfactory tubercle
- piriform cortex
- ant cortical amygdaloid nucleus (emotions)
- periamygdaloid cortex
- lat entorhinal cortex

Extrinsic projections
- lat hypothalamus (autonomic responses)
- hippocampus (memory)
- dorsomedial thalamic nucleus (discriminative interpretat.)
-

Question 10

5 main tastes + 1 candidate

Answer 10

Sweet (saccarides)
Salty (NaCl)
Sour (H+)
Bitter (complex) - related to sweet
Umami (glutamate)

“Fatty” taste (olive oil, fatty part of meat,…)

Question 11

Transduction mechanisms of flavors

Answer 11

Salty: Na channel
Sour: K channel block (by protons)
Sweet: G prot associated receptor, closes K channels, Ca release from reticulum (?)
Bitter: G prot associated receptor
Umami: glutamate receptor

Question 12

Receptors cells location

Answer 12

Taste buds

Question 13

Taste buds include

Answer 13

Gustatory cells
Supporting cells

(Synapse in gustatory fibers)

Question 14

Taste buds in the tongue

Answer 14

Grouped in papillae

Question 15

Taste buds in other parts of oral cavity (not in the tongue)

Answer 15

Scattered, no papillae

Question 16

Types of papillae

Answer 16

Filiform papillae = no taste buds! -> irregularities on
surface

Fungiform papillae: anterior 2⁄3, quite large, also have taste buds in lateral wall (anterolateral)

Circumvallate papillae: junction between post 1⁄3 - ant 2⁄3

Foliate papillae: indentations in post-lat (1⁄3) part of tongue

Question 17

Glands secreting saliva

Answer 17

Von Ebner glands, located in foliate + circumvallate papillae.

Question 18

Nerves that will carry sensation

Answer 18

Ant 2⁄3 of tongue = Chorda tympani, VII CN branch
- soma in geniculate ganglion (however, touch and Tª ->
lingual nerve, V branch)

Post 1⁄3 of tongue (taste and touch) = glossopharyngeal nerve (IX CN).
- soma in petrosal ganglion of the IX.

Oropharynx = Vagus, X CN, through sup laryngeal nerve.
- soma in Nodose ganglion

Question 19

Nucleus to which the 3 nerves carry the info (taste)

Answer 19

Solitary tract nucleus (NTS).
- Rostral part of NTS is —> taste
- Caudal part —> visceral info

Question 20

Flavour integration

Answer 20

From NTS -> taste inputs —> synapsis VPM —> insula —> orbitofrontal cortex (integration)

Olfaction = most of flavour we interpret from food
Somatosensory = texture of food + spicy / minty percept

Question 21

Taste disorders

Answer 21

Ageusa = no taste
Hypogeusa = reduction of taste
Dysgeusia = misinterpretation.

Question 22

Olfactory disorders

Answer 22

Anosmia = no olfaction
Hyposmia = reduction of olfaction
Parosmia = incorrect interpretation of smells
- Cacosmia = everything smells bad

Question 23

Examination of taste

Answer 23

Main tastes
Electrogustometry

Question 24

Examination of olfaction

Answer 24

Use non-irritating substances (irritation = somatosensory inputs)

Each nostril can be explored separately although there will always be some connection at the top between one and the other

Question 25

Synapsis of olfactory nerve fibers takes place in

Answer 25

Glomerulus

Question 26

Olfactory nerve fibers synapse with

Answer 26

Main neurons which I CN fibers contact with.
Generate axons that exit the bulb (output: olfactory tract ) 2 subtypes:
- Mitra cells
- Tufted cells

Periglomerular cells - around the glomeruli.

(Granule cells - synapse not w/ I CN but w/ Tufted & Mitral cells, also dendrodendritic synapses)

Question 27

Types of synapsis in olfactory bulb

Answer 27

Classical synapses
- dendro-axonic

Atypical synapses
- Mitra/Tufted with periglomerular cells
- dendrodendritic synapses
- bidirectional (NT release from 2 sides)
- only happens here

Question 28

Periglomerular cells can contact mitral and tufted cells through

Answer 28

Dendrodendritic synapses (on 1 end)

Axodendritic synapses (on the other end)

Question 29

Periglomerular and granule cells are

Answer 29

Inhibitory

Question 30

Regulation of olfactory pathway

Answer 30

By interneurons, where we can find special types of dendrodendritic synapses.

Question 31

Centrifugal projections - pathway

Answer 31

From:
- Locus coeruleus
- Raphe nuclei
- Olfactory cortex
Neurons enter olfactory tract and bulb
Descending projections through olfactory tract
Reach glomeruli + granule cells.

Question 32

Centrifugal projections - function

Answer 32

Modulate transmission of olfaction (regulating regulatory interneurons: granule + periglomerular cells)