Olfactory System

Question 1

What does the olfactory system detect?

Answer 1

Airborne molecules called odorants.

Question 2

What is olfactory epithelium?

Answer 2

• Specialized area within the olfactory mucosa located in the roof of the nasal cavity
• covered by a superficial acellular layer of mucus that contains soluble odorant binding proteins

Question 3

What are the components of the olfactory epithelium?

Answer 3

1. Olfactory Receptor Neurons
2. Supporting Cells
3. Basal Cells

Question 4

What is the structure of the olfactory receptor neurons, and what are its components?

Answer 4

• Bipolar Neuron
• Apical Dendrite
• Basal Axon

Question 5

Describe the apical dendrite of the olfactory receptor neuron.

Answer 5

Extends to the surface of the epithelium and terminates in a olfactory vesicle, from which cilia arise.
- Cilia contain receptors for odorant molecules

Question 6

Describe the basal axon of the olfactory receptor neuron.

Answer 6

• Extends from mucosa in bundles called olfactory fila which terminate in the olfactory bulb.
• Olfactory fila collectively form the olfactory nerve.

Question 7

What is the function of the olfactory receptor neurons?

Answer 7

Where olfactory transduction occurs

Question 8

What is the structure of the supporting cells?

Answer 8

Columnar epithelial cells located adjacent to the olfactory receptor neurons

Question 9

What is the function of the supporting cells?

Answer 9

• Mechanical support for olfactory receptor neurons

- Secretions to mucus that may play a role in binding or inactivation of odorant molecules

Question 10

What is the structure of the basal cells in the olfactory system?

Answer 10

Neural stem cells

- located at the base of the olfactory epithelium

Question 11

What is the function of the basal cells in the olfactory system?

Answer 11

Gives rise to the olfactory receptor neurons

Question 12

Explain the steps of olfactory transduction.

Answer 12

1. Odorants transported through the mucous by odorant binding proteins
2. Odorants bind to metabotropic receptors on olfactory cilia, opening (K+ and Ca++) channels, allowing them to flow into the cell
3. Depolarization travels down the dendrite to the cell body of olfactory receptor neuron. Large depolarization initiates an AP along the axon.

Question 13

Individual olfactory receptor neurons express how many types of odorant receptors?

Answer 13

1 type

Question 14

How are subtypes of odorant receptors distributed?

Answer 14

Within one of four bilaterally symmetric zones of the olfactory epithelium.

Question 15

Where does sensory information from the olfactory epithelium go?

Answer 15

To the olfactory bulb via the olfactory nerves.

Question 16

What are the pathways and target areas of the olfactory system?

Answer 16

Olfactory Bulb–> Olfactory Cortex–> Orbitofrontal Cortex

Question 17

Describe the structure of the olfactory bulb.

Answer 17

• Located on ventral surface of the frontal lobe
• Olfactory receptor neurons synapse on the dendrites of mitral and tufted cells in structures called olfactory glomeruli (glomerular layer)
• Axon of each receptor neuron synapses with only 1 glomerulus
• 1 golmerulus receives thousands of olfactory receptor axons that express the same type of odorant receptor. (Magnification is occurring)

Question 18

What is the job of interneurons in the olfactory system?

Answer 18

• Located between glomeruli

- May sharpen sensitivity of specific golmeruli to specific odorants

Question 19

What is the function of the olfactory bulb?

Answer 19

Where information is likely processed and refined

Question 20

Where do the axons of the mitral and tufted cells project to?

Answer 20

-Lateral olfactory tract to the ipsilateral and contralateral olfactory cortex

Question 21

Describe the structure of the olfactory cortex.

Answer 21

• 3 layers of cell bodies

- Includes: anterior olfactory nucleus, olfactory tubercle, pyriform cortex, amygdaloid, and entorhinal cortex

Question 22

What is the function of the olfactory cortex?

Answer 22

Information is likely processed and refined.

Question 23

Where does the information in the olfactory cortex project to?

Answer 23

• Olfactory bulbs (both sides), hippocampus, hypothalamus, dorsal medial nucleus (thalamus) and orbitofrontal cortex.

Question 24

What are hippocampal projections involved in?

Answer 24

Learning and behavior

Question 25

What are hypothalamus projections involved in?

Answer 25

Feeding behavior

Question 26

Where do the projections of the dorsal medial nucleus terminate?

Answer 26

Orbitofrontal cortex

Question 27

Where does the orbitofrontal cortex receive input from?

Answer 27

• Olfactory cortex directly
  OR
• Dorsal Medial Nucleus of Thalamus

Question 28

What is the function of the orbitofrontal cortex?

Answer 28

• Perception and discrimination of odors

- Site of integration fro taste, olfactory, and visual cues associated with the ingestion of food.

Question 29

What do the pathways in the orbitofrontal cortex insure?

Answer 29

Olfactory perception to influence cognitive, visceral, emotional, and homeostatic behaviors.

Question 30

What are disorders of smell called?

Answer 30

• Anosmia (absence)
• Hyposmia (decreased)
• Hyperosmia (increased)
• Dysosmia (distortion)

Question 31

What are the 4 unique features of the olfactory system?

Answer 31

1. Perception occurs at the orbitofrontal cortex
2. Cells regenerate
3. 3 layers in the olfactory cortex
4. Information doesn’t pass through the thalamus before going to the olfactory cortex.