Olfaction repeat

Question 1

What are the primary advantages of olfaction?

Answer 1

Locating and tracking food or prey from a distance.

Providing long-distance warnings beyond line-of-sight and in the dark.

Facilitating sexual attraction.

Activating the hedonic reward system, e.g., gastronomic delights like fine wine.

Question 2

What are some physiological and behavioral responses to odors?

Answer 2

Visceral responses: salivation and gastric motility when smelling food, gag reflex to noxious smells.

Infants recognize mothers by scent, and mothers recognize their babies.

Women housed together synchronize menstrual cycles (McClintock Effect).

Question 3

What are the key structures in the rat olfactory system?

Answer 3

Main olfactory epithelium (MOE): contains olfactory sensory neurons (OSNs), supporting cells, and basal stem cells.

Vomeronasal organ (VNO): targets accessory olfactory bulb (AOB).

Olfactory bulb (OB): processes signals from OSNs.

Question 4

How do olfactory sensory neurons (OSNs) function?

Answer 4

OSNs have apical dendrites capped by dendritic cilia in nasal cavity mucus.

Cilia contain receptor sites for odorant molecules, initiating olfactory signal transduction.

OSNs regenerate every 1-2 months from basal stem cells.

Question 5

Describe the olfactory signal transduction process.

Answer 5

1) Odorant binds to G protein-coupled receptors (GPCRs).

2) GPCR activates adenyl cyclase type-III, producing cAMP.

3) cAMP opens CNG cation channels, depolarizing the membrane.

4) Ca²⁺ influx opens Cl⁻ channels, amplifying the response.

Question 6

What makes olfaction unique among the senses?

Answer 6

Direct connection to the limbic system, bypassing the thalamus.

Strong ties to memory and emotion due to connections with the amygdala.

Question 7

What is the “one neuron, one receptor” rule in olfaction?

Answer 7

Each olfactory sensory neuron expresses only one functional olfactory receptor (OR) gene in a monoallelic manner.

Question 8

How is the specificity of olfactory receptor gene expression maintained?

Answer 8

Stochastic selection of OR genes.

Negative feedback ensures only one OR gene is expressed per neuron.

Question 9

What role does cAMP play in OSN axonal targeting?

Answer 9

OR-derived cAMP levels regulate axon-guidance molecules (e.g., Nrp1 and Sema3A).

High cAMP directs axons to posterior glomeruli, while low cAMP directs them to anterior glomeruli.

Question 10

How do humans recognize more than 10,000 odors with only ~1,000 olfactory receptors?

Answer 10

Odor perception relies on combinatorial coding, where each odor activates a unique combination of receptors.

Question 11

What is a chemotopic map in the olfactory bulb?

Answer 11

A spatial map of glomerular activation patterns reflecting odorant chemical domains and concentrations.

Question 12

What is specific anosmia?

Answer 12

he inability to smell one specific compound while having normal perception for other odors.

Question 13

What is the cribriform plate, and why is it significant in olfaction?

Answer 13

A bony structure with tiny holes separating the nose from the brain.

OSN axons pass through these holes to enter the brain, connecting to the olfactory bulb.

Question 14

What is the role of mitral cells in the olfactory bulb?

Answer 14

Mitral cells receive odor information from OSNs.

They refine, amplify, and relay the signal to higher brain areas.

Question 15

How do inhibitory interneurons contribute to olfactory processing?

Answer 15

Periglomerular cells connect glomeruli and provide lateral inhibition.

Granule cells connect mitral cells, refining the olfactory signal.

Question 16

How does olfactory adaptation work?

Answer 16

Ca²⁺ and other proteins regulate sensitivity to odorants.

Adaptation extends the range of odorant concentrations that can be detected.

Question 17

What is the relationship between odorant concentration and sensory neuron response?

Answer 17

Higher odorant concentrations increase the size and duration of inward current flow in sensory neurons, potentially triggering an action potential.

Question 18

What is the combinatorial code for odor perception?

Answer 18

Odors activate a specific set of glomeruli, creating a topographical activation map in the olfactory bulb.

This pattern encodes the identity of the odor.

Question 19

Why are specific stereoisomers perceived differently in olfaction?

Answer 19

Slight differences in molecular structure can alter how an odorant interacts with olfactory receptors, changing the perceived odor.

Question 20

What ensures correct glomerular targeting of OSN axons?

Answer 20

Activity-dependent refinement involving adhesive and repulsive molecules.

Axon fasciculation and segregation finalize the glomerular map.

Question 21

What is the role of the locus control region (LCR) in olfactory receptor gene expression?

Answer 21

LCR stochastically selects one OR gene for expression.

It prevents the transcription of additional OR genes in the same neuron.

Question 22

What experimental evidence supports the role of cAMP in OSN axon targeting?

Answer 22

Mutants with altered cAMP levels show mistargeting of axons.

cAMP regulates axon-guidance molecules like Nrp1 and Sema3A.

Question 23

How does the olfactory system achieve sensitivity to a vast range of odorants?

Answer 23

Amplification: One odorant molecule can activate multiple G proteins and cAMP molecules.

Adaptation: Ca²⁺ and other proteins modulate receptor sensitivity.