Lecture 23: Chemical senses

Question 1

Olfactory epithelium are actually…Where do these cells project?

Answer 1

The olfactory nerve cells; sends rootlets (axons) through the cribiform plate to the olfactory bulb

Question 2

Where is the first synapse in the olfactory system?

Answer 2

Between the olfactory bulb and the axons of the olfactory epithelium

Question 3

The olfactory bulb is considered part of the…

Answer 3

CNS

Question 4

What does the olfactory system lack?

Answer 4

Thalamic relay

Question 5

Where does the olfactory tract travel to?

Answer 5

Directly into olfactory cortex (piriform cortex: uncus, amygdala, parahippocampal gyrus)

Question 6

Where does the olfactory cortex project?

Answer 6

Orbitofrontal cortex, thalamus, hypothalamus; entorhinal –> hippocampus

Question 7

About half of the nasal cavity is what? What’s the other half?

Answer 7

Respiratory and olfactory epithelium

Question 8

Odorants bind to…this gets turned into?

Answer 8

Receptors on olfactory epithelium cilia –> AP

Question 9

What is a basal cell?

Answer 9

Stem cells to make new olfactory receptor neurons

Question 10

In olfactory epithelium, you find…(4)

Answer 10

Receptor cells, basal cells, supporting cells, Bowman’s glands (make protective mucus)

Question 11

Olfactory receptors and odor discrimination

Answer 11

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

Question 12

Olfactory nerve is mostly ipsi/contralateral

Answer 12

Ipsilateral

Question 13

First layer of olfactory bulb contains the (what happens here?)…What’s the name of the second cell? What’s it’s function?

Answer 13

Glomerulus (first synapse); mitral cells; principal projection neurons

Question 14

T/F: There is top-down processing in olfactory bulb. What type of cell?

Answer 14

True! Suppresses background smells; granule cell

Question 15

What things do olfactory cortex projections do? (3)

Answer 15

Hippocampus: Olfactory-guided memory; Hypothalamus: feeding behavior, ANS responses; Cortex: discrimination/identification of odors

Question 16

Unique attributes of olfactory system (4)

Answer 16

1. 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

Question 17

What are two physical responses to odorants?

Answer 17

1. Visceral motor responses to food; 2. Reproductive/endocrine functions (menstrual cycles, mother-child interactions, pheromones)

Question 18

Olfactory agnosia

Answer 18

Aware of smell but not of name

Question 19

Cacosmia

Answer 19

Formation of repugnant/disagreeable olfactory auras

Question 20

Parosmia/Dysosmia

Answer 20

Distortion in a smell

Question 21

Causes of anosmia, hyposmia

Answer 21

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

Question 22

Causes of hallucinations, cacosmia, parosmia

Answer 22

Epilepsy, psychiatric disorder

Question 23

Causes of hyperosmia

Answer 23

Migraine, psychosis, substance use

Question 24

Where does taste information go from solitary nucleus? Where from here?

Answer 24

VPM of thalamus –> insula (gustatory cortex) and frontal cortex (interprets what you’re eating)

Question 25

Solitary nucleus also projects to…

Answer 25

Hypothalamus (regulation of eating), amygdala (emotional response to food)

Question 26

Taste _____ are located within taste ________

Answer 26

Buds; papillae

Question 27

How are taste buds replaced?

Answer 27

Basal cells

Question 28

What is a common misconception of the tongue taste system?

Answer 28

All tastes can be detected over the entire surface of the tongue but regions have varying thresholds for each taste

Question 29

How do we distinguish types of taste?

Answer 29

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

Question 30

Transduction of taste information starts where on the taste bud? Then what? First synapse?

Answer 30

Apical domain; electrical signals are generated at basal domain via graded receptor potentials and NT release; synapses on primary afferent axons of CNs

Question 31

Primary gustatory cortex includes which two brain regions…(2)

Answer 31

Anterior insula and frontal operculum

Question 32

Ageusia

Answer 32

Complete loss of taste (rare)

Question 33

Hypogeusia

Answer 33

Decreased taste (normal aging)

Question 34

Parageusia/dysgeusia

Answer 34

Unpleasant perception of taste when it normally taste good (common after chemotherapy or in elderly)

Question 35

Cacogeusia

Answer 35

Perception of an unpleasant taste (often seizure in insula/operculum)

Question 36

Gustatory hallucinations

Answer 36

Tasting when no taste present (migraines, seizures, psychiatric: though rare)

Question 37

A tumor where could cause taste disturbance? These often lead to taste loss on one/both sides?

Answer 37

Internal auditory meatus (compressing CN VII), oropharyngeal tumors; ipsilateral tumor

Question 38

Some other causes of taste problems (4)

Answer 38

Bell’s palsy, head trauma, radiation therapy, diabetes