Olfaction Pathways

Question 1

How many different odorants can be distinguish? With how many receptors? Controlled by how many genes?

Answer 1

10,000 odorants

1000 receptors

330 genes (3% of genome - largest single group of receptors)

Question 2

What determines the receptors an odorant will activate?

Answer 2

molecular structure

Question 3

Where are the receptors for olfaction located?

Answer 3

in the nasal olfactory epithelia at the roof of the nose

Question 4

Olfaction is considered a special sense in that it has a special sensory organ, but why makes it less special than, say, vision?

Answer 4

there are no specialized receptor cells releasing neurotransmitters - the receptor proteins are on the olfactory receptor neurons themselves

Question 5

What makes olfactory neurons unique int he CNS?

Answer 5

they are the only ones that are routinely turned over and replaced

Question 6

Where do the olfacory primary afferents synapse?

Answer 6

run up through the cribiform plate to the olfactory bulb

Question 7

Describe the steps in olfactory transduction

Answer 7

1. odorant enters nose
2. chaperones help odorant get to the appropriate receptors
3. binding to the receptors
4. G protein (G-olf) activated
5. G-olf turns on adenylyl cyclase
6. adenylyl cyclase increases cAMP
7. cAMP opens the channel
8. nonselective cation chanel open to allow Na+ in
9. depolarization results in receptor potential and subsequent action potential

Question 8

What is the issue in terms of labelled line in the olfactory system? How does the system compensate for this?

Answer 8

there are more recognizable odorants than there are receptors, which would throw a wrench into labelled line

the system compensates for this quite easily actually

1 odorant will be capable to activating more than 1 receptor, so the brain responds and interprets the PATTERN of the receptor activation as opposed to single receptor activation alone

this is pattern coding

Question 9

WHere is the odortypic map first established?

Answer 9

in the olfactory bulb

(fibers get organized out into specific glomeruli)

Question 10

What are the secondary neurons called and where are their cell bodies?

Answer 10

mitral cells - cell bodies in the olfactory bulb, processes in the olfactory tract

Question 11

How are the mitral cells packaged?

Answer 11

they’re clustered into glomeruli which get information from similar receptors - the start of the odotopic map

Question 12

What are the 3 general pathways olfactory fibers will take into the brain?

Answer 12

to the piriform cortex (primary olfactory cortex(

amygdala (and hypothalamus)

enterohinal cortex (and hippocampus)

Question 13

Describe the pathwaythroguht he piriform cortex and it’s main role.

Answer 13

From the olfactory bulb, project to the piriform cortex in the tip of the uncus

then some (but not all) of the fibers go through the medial Dorsal nucleus of the thalamus

then to the orbitofrontal cortex (located above the eyeball)

This serves to integrate taste and smell, giving you flavor and CONSCIOUS AWARENESS OF SMELL

Question 14

Describe the pathway through the amygdala and its’ purpose.

Answer 14

soe of the fibers run through the olfacotry tubercle to the amygdala, then on to the hypothalamus

this controls the visceral and homeostatic reactions to smell - basically getting the GI system ready to eaT

SUBCONSCIOUS SMELL

Question 15

Describe the pathway through the entorhinal cortex and its purpose.

Answer 15

some fibers will go through the entorhinal cortex to the hippocampus

this is where we form the memories of smell