Olfaction And Taste Flashcards
Receptor organ for olphaction
Olfactory epithelium
Olfactory epithelium - cell types
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
Why do we have mucus layer?
Odorant substances need to dissolve in order to be recognized
Input pathway
Axons of olfactory neurons enter small grooves -> cross cribriform plate of ethmoid bone -> olfactory bulb: synapse -> input to brain through olfactory tract
Olfactory system receptor
Proper neuron
Olfactory transduction
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
How many different olfactory receptors do we have?
Unknown, only 1 receptor type per neuron
Organization of olfactory bulb
Fibres (input) reach the periphery of the olfactory bulb
Processing from periphery to centre
Output of the bulb exits from the centre
Olfactory cortex
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.)
-
5 main tastes + 1 candidate
Sweet (saccarides)
Salty (NaCl)
Sour (H+)
Bitter (complex) - related to sweet
Umami (glutamate)
“Fatty” taste (olive oil, fatty part of meat,…)
Transduction mechanisms of flavors
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
Receptors cells location
Taste buds
Taste buds include
Gustatory cells
Supporting cells
(Synapse in gustatory fibers)
Taste buds in the tongue
Grouped in papillae
Taste buds in other parts of oral cavity (not in the tongue)
Scattered, no papillae
Types of papillae
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
Glands secreting saliva
Von Ebner glands, located in foliate + circumvallate papillae.
Nerves that will carry sensation
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
Nucleus to which the 3 nerves carry the info (taste)
Solitary tract nucleus (NTS).
- Rostral part of NTS is —> taste
- Caudal part —> visceral info
Flavour integration
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
Taste disorders
Ageusa = no taste
Hypogeusa = reduction of taste
Dysgeusia = misinterpretation.
Olfactory disorders
Anosmia = no olfaction
Hyposmia = reduction of olfaction
Parosmia = incorrect interpretation of smells
- Cacosmia = everything smells bad
Examination of taste
Main tastes
Electrogustometry
Examination of olfaction
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
Synapsis of olfactory nerve fibers takes place in
Glomerulus
Olfactory nerve fibers synapse with
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)
Types of synapsis in olfactory bulb
Classical synapses
- dendro-axonic
Atypical synapses
- Mitra/Tufted with periglomerular cells
- dendrodendritic synapses
- bidirectional (NT release from 2 sides)
- only happens here
Periglomerular cells can contact mitral and tufted cells through
Dendrodendritic synapses (on 1 end)
Axodendritic synapses (on the other end)
Periglomerular and granule cells are
Inhibitory
Regulation of olfactory pathway
By interneurons, where we can find special types of dendrodendritic synapses.
Centrifugal projections - pathway
From:
- Locus coeruleus
- Raphe nuclei
- Olfactory cortex
Neurons enter olfactory tract and bulb
Descending projections through olfactory tract
Reach glomeruli + granule cells.
Centrifugal projections - function
Modulate transmission of olfaction (regulating regulatory interneurons: granule + periglomerular cells)
