Lecture 23: Chemical senses Flashcards
Olfactory epithelium are actually…Where do these cells project?
The olfactory nerve cells; sends rootlets (axons) through the cribiform plate to the olfactory bulb
Where is the first synapse in the olfactory system?
Between the olfactory bulb and the axons of the olfactory epithelium
The olfactory bulb is considered part of the…
CNS
What does the olfactory system lack?
Thalamic relay
Where does the olfactory tract travel to?
Directly into olfactory cortex (piriform cortex: uncus, amygdala, parahippocampal gyrus)
Where does the olfactory cortex project?
Orbitofrontal cortex, thalamus, hypothalamus; entorhinal –> hippocampus
About half of the nasal cavity is what? What’s the other half?
Respiratory and olfactory epithelium
Odorants bind to…this gets turned into?
Receptors on olfactory epithelium cilia –> AP
What is a basal cell?
Stem cells to make new olfactory receptor neurons
In olfactory epithelium, you find…(4)
Receptor cells, basal cells, supporting cells, Bowman’s glands (make protective mucus)
Olfactory receptors and odor discrimination
In general, individual olfactory neurons express only one type of odorant receptor and specific subtypes of odorant receptors preferentially distribute within one of four bilaterally symmetric zones of the olfactory epithelium
Olfactory nerve is mostly ipsi/contralateral
Ipsilateral
First layer of olfactory bulb contains the (what happens here?)…What’s the name of the second cell? What’s it’s function?
Glomerulus (first synapse); mitral cells; principal projection neurons
T/F: There is top-down processing in olfactory bulb. What type of cell?
True! Suppresses background smells; granule cell
What things do olfactory cortex projections do? (3)
Hippocampus: Olfactory-guided memory; Hypothalamus: feeding behavior, ANS responses; Cortex: discrimination/identification of odors
Unique attributes of olfactory system (4)
- Somas of parimry afferent neurons occupy surface epithelium; 2. Axons enter cortex directly; 3. Primary afferent neurons undergo continuous turnover; 4. Pathway to cortical centers is ipsilateral
What are two physical responses to odorants?
- Visceral motor responses to food; 2. Reproductive/endocrine functions (menstrual cycles, mother-child interactions, pheromones)
Olfactory agnosia
Aware of smell but not of name
Cacosmia
Formation of repugnant/disagreeable olfactory auras
Parosmia/Dysosmia
Distortion in a smell
Causes of anosmia, hyposmia
URI (mucus blocks access of odorants), trauma (cribiform plate: ethmoid bone, look for Raccoon Eyes or CSF Rhinorrhea), tumors (neuroblastomas, meningiomas), aging (normal)/neurodegenerative (early clue to Alzheimer’s, Parkinson’s), toxins/medications/drugs/smoking
Causes of hallucinations, cacosmia, parosmia
Epilepsy, psychiatric disorder
Causes of hyperosmia
Migraine, psychosis, substance use
Where does taste information go from solitary nucleus? Where from here?
VPM of thalamus –> insula (gustatory cortex) and frontal cortex (interprets what you’re eating)
Solitary nucleus also projects to…
Hypothalamus (regulation of eating), amygdala (emotional response to food)
Taste _____ are located within taste ________
Buds; papillae
How are taste buds replaced?
Basal cells
What is a common misconception of the tongue taste system?
All tastes can be detected over the entire surface of the tongue but regions have varying thresholds for each taste
How do we distinguish types of taste?
Each tastant category corresponds to a distinct class of receptor molecules expressed in subsets of taste cells which are also maintained in the representation of taste information in the CNS
Transduction of taste information starts where on the taste bud? Then what? First synapse?
Apical domain; electrical signals are generated at basal domain via graded receptor potentials and NT release; synapses on primary afferent axons of CNs
Primary gustatory cortex includes which two brain regions…(2)
Anterior insula and frontal operculum
Ageusia
Complete loss of taste (rare)
Hypogeusia
Decreased taste (normal aging)
Parageusia/dysgeusia
Unpleasant perception of taste when it normally taste good (common after chemotherapy or in elderly)
Cacogeusia
Perception of an unpleasant taste (often seizure in insula/operculum)
Gustatory hallucinations
Tasting when no taste present (migraines, seizures, psychiatric: though rare)
A tumor where could cause taste disturbance? These often lead to taste loss on one/both sides?
Internal auditory meatus (compressing CN VII), oropharyngeal tumors; ipsilateral tumor
Some other causes of taste problems (4)
Bell’s palsy, head trauma, radiation therapy, diabetes
