Olfactory- complete

Question 1

Odorants

Answer 1

small, volatile, hydrophobic molecules that bind to olfactory receptor neurons, inhaled from air, travel into to nasal cavity.

Question 2

Each nasal cavity contains

Answer 2

olfactory sensory epithelium.

Question 3

odorants bind to olfactory receptor neurons in

Answer 3

OSE or Olfactory sensory Epithelium

Question 4

What causes transduction of a signal in olf neurons?

Answer 4

odorants binding to olfactory receptor neurons cause transduction in these neuronal cells.

Question 5

transduction

Answer 5

a physical stimulation is converted to an electrical signal

Question 6

OSE = Olfactory Sensory Epithelium resembles

Answer 6

respiratory epithelium. nasal passage is anatomically connected to respiratory compartments.

Question 7

OSE consists of what kind of cells?

Answer 7

• pseudo stratified columnar epithelium
• with a ciliated apical portion

Question 8

The major difference between olfactory and respiratory epithelium

Answer 8

no neuronal component in respiratory; Cilia of OSE has receptors for odorants and the cilia processes extend into mucus layer

Question 9

OSE contains these cells

Answer 9

support cells + basal cells (give rise to the olfaction cells)

Question 10

location of OSE in relation to palate, olf bulb and plate

Answer 10

OSE is superior to the palate, olfactory bulb sits superior to the cribriform plate. cilia from the olfactory cells are embedded in the mucus layer

Question 11

How are OSE cells connected to the higher neuron structures?

Answer 11

• Axons from olfactory receptor cells (in OSE) protrude through the cribriform plate of the ethmoid bone
• Then axons fasciculate/converge to form olfactory nerves
• Olf nerves travel to the olfactory bulb.
• Olf Bulb gives rise to olf tracts

Question 12

Olfactory receptor cells/neurons

Answer 12

highly differentiated; each odorant receptor neuron (ORN) expresses 1 odorant receptor type, so only sensitive to a subset of odorants.

Question 13

One odorant can activate

Answer 13

combination of different receptors

Question 14

What gives olfaction its high degree of plasticity?

Answer 14

• 1 odorants can activate different receptors
• smells cause different degree of activation of certain receptor types.

Question 15

Signal transduction in ORNs

Answer 15

** Mediated by GCPRs**

1. Odorants bind G-alpha olf GCPR
2. activates adenylyl cyclase –> activates cAMP-> intracellular cAMP inc
3. cAMP binds + opens cyclic nucleotide gated (CNG) cation channels (nonselective: Na+ and Ca+ can flow in, Cl- can flow out).
4. Cations in/ anions out = depolarization of ORN

Question 16

What causes depolarization of ORNs? AP?

Answer 16

1) Odorant binding increases intracellular cAMP
2) cAMP gated cation channels open [nonselective ch, Na+ and Ca+ can flow in, Cl- can flow out].
3) Cations in/ anions out (negative leaving cell) = depolarization!
4) If depol reaches threshold, AP occurs in the olf cells, and is transmitted to the olfactory nerves.

*(cAMP gated ch = cyclic nucleotide gated = CNG)

Question 17

Topography of the Olfactory Bulb

Answer 17

Within the bulb are glomeruli = specialized cluster of synapses. Convergence of 1 type of olfactory receptor cells/glomerulus.

Question 18

Topography is preserved in _____ but not ___

Answer 18

preserved in amygdala, but not in the piriform cortex.

Question 19

Also synapsing within the glomeruli are

Answer 19

mitral and tufted cells.

Question 20

Which cells within the olf bulb gives rise to the lateral tracts?

Answer 20

Mitral and tufted cells give rise to lateral olfactory tracts that go the olfactory cortex.

Question 21

bilateral symmetry means what?

Answer 21

The Olfactory bulb exhibits bilateral symmetry, so each side leads to a lateral tract. No crossing over, except the occasional mitral cell collateral.

Question 22

periglomerular cells

Answer 22

support cells within the olfactory bulb

Question 23

Info from Olfactory Bulb is sent to these targets:

Answer 23

1) piriform cortex- main target tissue.
2) amygdala- important for emotional memory and the limbic system.
3) hippocampus- major input, associated with memory, learning.
4) olfactory tubercle
5) Entorhinal cortex (–> hippo)

Question 24

How does thalamus receive olfactory input?

Answer 24

indirect input from the olfactory bulb, via amygdala.

Question 25

Evidence that memory and smell are related

Answer 25

input from olfactory bulb to

1) hippocampus – memory, learning
2) amygdala– emotional memory, limbic system

Question 26

Unilateral nature of the olfactory bulb

Answer 26

two lateral olfactory tracts that come out of the bulb and go to either side of the brain.

Question 27

2 major differences bw gustatory/taste and olfactory/smell

Answer 27

1) in olf, there is a DIRECT pathway to higher processing centers in the brain, info does NOT pass through thalamus before reaching cortex, indicates that smell is one of the oldest senses.
2) olfaction is linked to memory structures in the brain.

Question 28

Anosmia

Answer 28

• lack of olfactory sense, inability to smell
• can be temporary or permanent.

Causes:

• Trauma - can sheer the OSE from the ethmoid bone
• Illness/blockage of nasal passage due to mucous

Question 29

Phantosmia

Answer 29

olfactory hallucinations. Causes - either central or peripheral NS problem

Question 30

Pheromones

Answer 30

• volatile compounds
• activate vomero-nasal organ (residual in humans), then OSE and go on to the accessory olfactory bulb (Not in humans).
• In women who cohabitate, pheromones extend/delay length of menstrual cycle = synchronization of menstrual cycles