lecture 14 Flashcards
The olfactory system
- 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
cilia projects ______ into _______ ________ and have __________
- downwards
- mucous layer
- oderent receptor proteins
how many odorant receptors do we have
400
odorant molecules enter _______ _______ and dissolve
mucus layer
what can you find in the tips of dendrites
- GCPRs
- they bind to ligand that activate them and these ligands are smells
Signal transduction in the olfactory system
- oderant molecule binds to g-protein coupled receptor (Golf)
- which causes adenylyl cyclase to activate
- adenylyl cyclase converts ATP in cyclic AMP (cAMP)
- cAMP opens cyclic nucleotide gated NA+ channels (CNG channels) which allows Na+ to rush in and depolarize
and cause a receptor potential - sufficient receptor potential produces an action potential at the axon hillock
what is one exception that differs in the olfactory pathway
the olfactory pathways bypasses the thalamus
Type 1 receptors (taste sensors)
- 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
Type 2 receptor cells (taste sensors)
- 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
Type 3 receptor cells (taste sensors)
- 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
Taste transduction (Type 2)
- sweet, umami, and bitter ligand bind to GCPR (which are all different depending on which flavour)
- signal transduction
- release of Ca2+ from intracellular stores and ECF into type 2 receptor cell
- Ca2+ triggers ATP release and ATP will act on partner primary neuron that will cause AP
Signal transduction (Type 3)
- H+ enters which causes depolarization and a drop in pH
- release of Ca2+ from ECF and triggers exocytosis of neurotransmitter serotonin which acts on partner primary neurons to fire AP
what are the 2 ducts surrounding the cochlear duct
- Tympanic duct
- Vestibular duct
- They are filled with perilymph and have a composition of ECF
what duct lies between the tympanic and vestibular duct
The cochlear duct which is filled with endolymph which has a similar composition to ICF which has high k+
where are the auditory receptors located
the organ of corti
the organ of corti project into
endolymph
what happens at the organ of corti
- signal transduction
- receptor potential produced in specialized sensory cells (not neurons)
What is the tectorial membranea
a flap that folds over of the organ of corti and all hair cells are embedded in tectorial membrane
hair cells are
- have cilia
- specialized receptor cells
- used for transduction
what kind of channels live in the tips of cilia and why
- 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
cilia is linked by
- big extracellular proteins that are called tip links
- since they’re all linked when you pull on one you pull on all
when we open our mechanically gated ion channels
- k+ will go and we’ll generate a receptor potential
Detecting different sound frequencies/pitch
Near the oval window: stiff, more sensitive to high frequency
At helicotrema: greater flexibility to low frequency
regional differences (example)
when you activate the organ of corti near the oval window this will be perceived as high frequency
The auditory pathway
- right and left cochlea (cross over)
- pons
- midbrain
- thalamus
- left and right auditory cortex
