10/6 Smell and Taste (McIntyre)

Question 1

• Know the Pathways of Olfactory and Taste Systems to the brain

Answer 1

1. Olfactory subsystems—general chemical odorants, peptides, pheromones. Gustatory system—nonvolatile biologically relevant compounds. Trigeminal—polymodal nociceptive neurons that detect chemical irritance (ammonia, etoh, capsaicin). Olfactory epithelium is a sensory epithelium for detecting odors. OSNs project from periphery to CNS via cranial nerve I. Taste modalities carried by different pathways. Ion channels—salt: eNAC, sour: Otop1. GPCRs—Sweet: T1R2, T1R3. Umami: T1R1, T1R3. Bitter: T2Rs, 40 genes.

Question 2

• Detail the structures that process these signals as they ascend through the chemosensory neuroaxis.

Answer 2

1. Bony structures in nasal cavities called turbinates. Increase surface area, air flow across neurons.Olfactory epithelium senses odors. Pseudostratified epithelium is neuronal and non neuronal cells. Sustentacular cells (~15%) are supporting cells. Olfactory Sensory neurons (OSNs) (~75%) signal transducing (bipolar cells), dendritic ending is in outside of brain, limited lifespan (why covid smell loss is temporary). Bowman’s gland (BG) cells excrete essential components.

Question 3

• Describe the layers of the olfactory bulb

Answer 3

1. Mitral and tuft cells are output neurons, periglomerular and granule cells make lateral interconnections among mitral and tuft cells

Question 4

• Understand the general logic of odor and taste coding in higher brain regions

Answer 4

1. Odor information goes to several places: olfactory receptors go through CN I to the olfactory bulb then tract to pyriform cortex, olfactory tubercle, amygdala, and entorhinal cortex. Pyriform goes to orbitofrontal cortex then thalamus. All go to orbitofrontal cortex, thalamus, and hypothalamus, entorhinal cortex goes to hpc formation. Input to cortex is not topographical: distributed interconnections between pyramidal cells. Spatially distributed activity. Synaptic plasticity regulated by forebrain inputs.

Question 5

• Describe the anatomy of the primate gustatory system

Answer 5

1. The gustatory system is responsible for particular nonvolatile biologically relevant chemical compounds. Carried from tongue and mouth by CN 7,9,10. All project to nuc of solitary to medial n of thalamus. from thalamus they go to gustatory cortex (insula) to main cortex.

Question 6

• Describe causes for chemosensory disorders

Answer 6

1. Conductive: inflammatory, trauma, neoplasia, congenital.
2. Sensorineural: trauma, degenerative-Age, toxic, endocrine-metaolic, neoplasia, congenital
3. Ciliopathies: defects in structure or function of cilia
4. Channelopathies: dysfunction in ion channels
5. Developmental: failure of OSN axons to grow to bulb; ob to develop (Kallman)

Question 7

• List the types of taste cells

Answer 7

1. Type I: several molecules characteristic of glia in CNS. Subset implicated in salt detection. Type II: GPCRsdownstream signaling—sweet, umami, bitter. Type III: detection of acids, integration of signals from type II cells—sour.