lecture 14

Question 1

The olfactory system

Answer 1

• uses free nerve endings (are neurons)
• primary neurons are the ones that do the sensing
  1. olfactory neurons have cilia which is where u can find the receptors. They also contain the odorant receptor protein that detect the odor
  2. the primary neurons project up through the ethmoïdal home to find the olfactory bulb
  3. olfactory bulb is where the olfactory neuron synapse to the secondary neuron
  4. and project via olfactory tract to the olfactory cortex

Question 2

cilia projects ______ into _______ ________ and have __________

Answer 2

1. downwards
2. mucous layer
3. oderent receptor proteins

Question 3

how many odorant receptors do we have

Answer 3

400

Question 4

odorant molecules enter _______ _______ and dissolve

Answer 4

mucus layer

Question 5

what can you find in the tips of dendrites

Answer 5

• GCPRs
  
  • they bind to ligand that activate them and these ligands are smells

Question 6

Signal transduction in the olfactory system

Answer 6

1. oderant molecule binds to g-protein coupled receptor (Golf)
2. which causes adenylyl cyclase to activate
3. adenylyl cyclase converts ATP in cyclic AMP (cAMP)
4. cAMP opens cyclic nucleotide gated NA+ channels (CNG channels) which allows Na+ to rush in and depolarize
   and cause a receptor potential
5. sufficient receptor potential produces an action potential at the axon hillock

Question 7

what is one exception that differs in the olfactory pathway

Answer 7

the olfactory pathways bypasses the thalamus

Question 8

Type 1 receptors (taste sensors)

Answer 8

• are support cells
• they are salt sensing because they have Na+ channels, so when sodium is there and enters the channels. these cells will send a signal that the meal is salt

Question 9

Type 2 receptor cells (taste sensors)

Answer 9

• has different types of specialized receptor cells that express different GPCRs
• the different flavours are: sweet, umami, bitter
• they then release neurotransmitter which is ATP that acts on primary neuron

Question 10

Type 3 receptor cells (taste sensors)

Answer 10

• responsible for sour (HCl
• through expression of proton channels (H+) that allow the sensing of acidity through opening of these channels
• will then release neurotransmitter that is serotonin that acts on partner primary neuron that will then cause firing

Question 11

Taste transduction (Type 2)

Answer 11

1. sweet, umami, and bitter ligand bind to GCPR (which are all different depending on which flavour)
2. signal transduction
3. release of Ca2+ from intracellular stores and ECF into type 2 receptor cell
4. Ca2+ triggers ATP release and ATP will act on partner primary neuron that will cause AP

Question 12

Signal transduction (Type 3)

Answer 12

1. H+ enters which causes depolarization and a drop in pH
2. release of Ca2+ from ECF and triggers exocytosis of neurotransmitter serotonin which acts on partner primary neurons to fire AP

Question 13

what are the 2 ducts surrounding the cochlear duct

Answer 13

• Tympanic duct
• Vestibular duct
• They are filled with perilymph and have a composition of ECF

Question 14

what duct lies between the tympanic and vestibular duct

Answer 14

The cochlear duct which is filled with endolymph which has a similar composition to ICF which has high k+

Question 15

where are the auditory receptors located

Answer 15

the organ of corti

Question 16

the organ of corti project into

Answer 16

endolymph

Question 17

what happens at the organ of corti

Answer 17

• signal transduction
• receptor potential produced in specialized sensory cells (not neurons)

Question 18

What is the tectorial membranea

Answer 18

a flap that folds over of the organ of corti and all hair cells are embedded in tectorial membrane

Question 19

hair cells are

Answer 19

• have cilia
• specialized receptor cells
• used for transduction

Question 20

what kind of channels live in the tips of cilia and why

Answer 20

• mechanically gated ion channels because when a wave of fluid comes along the tectorial memebrane and basilar membrane will be displace and will push and pull on cilia

Question 21

cilia is linked by

Answer 21

• big extracellular proteins that are called tip links
• since they’re all linked when you pull on one you pull on all

Question 22

when we open our mechanically gated ion channels

Answer 22

• k+ will go and we’ll generate a receptor potential

Question 23

Detecting different sound frequencies/pitch

Answer 23

Near the oval window: stiff, more sensitive to high frequency
At helicotrema: greater flexibility to low frequency

Question 24

regional differences (example)

Answer 24

when you activate the organ of corti near the oval window this will be perceived as high frequency

Question 25

The auditory pathway

Answer 25

1. right and left cochlea (cross over) 2. pons 3. midbrain 4. thalamus 5. left and right auditory cortex