lecture 14- chemoreception and auditory system, sensory II Flashcards
Sensory receptor in olfactory system
= olfactory neuron (primary neuron)
What is olfaction
smell
olfactory cilia (dendrites) contain
odorant receptor proteins
and they project downwards into the mucous layer
axons project upwards though the —- in olfactory neurons
lamina propria and bone
the olfactory neurons synapse with the
secondary sensory neurons in the olfactory bulb
olfactory neurons only live in the olfactory epithelium for about
2 months, after that they are replaced by new neurons whose axons need to find a way into the olfactory bulb
what carries info to the olfactory bulb?
olfactory neuron axons (cranial nerve I)
the basal cell layer includes —- that replace olfactory neurons
stem cells
what must dissolve in the mucous layer?
odorant molecules
what do odorant receptors do once they enter the mucus layer and dissolve?
they bind to specific odorant receptors that are located on the cell membrane of dendrites
humans have about —- different odorant receptors
400
what are odorant receptors
GPCRs and they are all linked to specialized G proteins
each neuron expresses —- type of odorant receptor
only 1
combinations of activated receptors and neurons allow us to smell —– odors
about 5000
a perceived odor may involve a combination of —–
types of odorant receptors
signal transduction in the olfactory system
(how is an AP produced in 5 steps)
- odor molecule binds to a GPCR
- activated G protein (Golf) activates adenylyl cyclase
- adenylyl cyclase converts ATP to cAMP
- cAMP opens cyclic nucleotide-gated Na+ channels
- sufficient receptor potential produces an action potential at the axon hillock
explain why the olfactory system is linked with the limbic system and cerebral cortex
smell is linked with emotion and memory
does the olfactory pathway go through the thalamus?
NO!! the olfactory pathway bypasses the thalamus
explain the pathway of the olfactory system using anatomy
olfactory neurons in the olfactory epithelium
cranial nerve I
olfactory bulb
olfactory tract
olfactory cortex
–> the cerebral cortex and limbic system
gustatory system
taste
each taste bud= — taste cells
50-150
each taste bud is composed of
taste cells joined near the apical surface with tight junctions
taste ligands create — signals that release —-
Ca2+ signals that release serotonin or ATP
taste cells are…
non-neuronal and each is sensitive to a particular taste ligand
taste cells are polarized: receptor potential at the apical membrane; communicates with primary sensory neuron at the basal membrane
the intracellular pathway is — for every type of taste cell
different
5 tastes
sweet, salty, bitter, sour, umami
type I support cells may sense
salt when Na+ enter through channels
receptor cells with GPCR membrane receptors bind either…
bitter, sweet or umami ligands and release ATP as a signal molecule
type 2 cells/receptors express GPCRs for either
sweet, umami or bitterness
Gustatory system: which nerves are signals carried along?
facial (VII), glossopharyngeal (IX) and vagus (X) cranial nerves
describe the 5 steps of gustatory signal transduction
- ligands activate the taste cell
- various intracellular pathways are activates
- Ca2+ signal in the cytoplasm triggers exocytosis or ATP formation
- NT or ATP is released
- Primary sensory neuron fires and AP are sent to the brain
gustatory system route of signal
through the thalamus and then gustatory cortex
what is signal transduction
how an AP is produced
auditory system: what is sound?
sound is the perception and interpretation of air waves
(specifically pressure waves)
pressure waves= sinusoidally varying density of air molecules
amplitude determines
volume
bigger amplitude= louder (dB)
frequency determines
pitch
high frequency= higher pitch (Hz)
Ear anatomy: pinna
the pinna directs sound waves into the ear
the outer ear
an air filled space.
the pinna acts as a funnel for sound waves
tympanic membrane
separates outer and middle ear “drum”
middle ear contains
incus, malleus and stapes
( 3 smallest bones in the body)
air filled space
oval window
IN
round window
OUT
explain how a pressure wave is converted to a fluid wave
the pinna guides pressure waves in
the wave strikes the tympanic membrane
the tympanic membrane taps on the malleus, taps on the incus, incus taps on stapes and stapes taps on the oval window
the oval window converts mechanical energy to fluid energy
fluid waves push the flexible membrane of the cochlear duct. hair cells bend and ion channels open. Electrical signal alters NT release
NT release onto sensory neurons create an AP that travels through the cochlear nerve to the brain
then a fluid wave is expelled out the round window
the inner ear is — filled
fluid-filled
the oval window and the round window separate the —– from the —
fluid-filled inner ear from the air-filled middle ear
the cochlea
“unroll” it to view the structures
cochlear duct is filled with endolymph
vestibular and tympanic ducts are filled with perilymph
-round window, tympanic duct, basilar membrane, helicotrema (apex)
perilymph is like
ECF
- similar composition to plasma
endolymph is like
ICF
- K+
helicotrema (ear anatomy)
is the tip where endolymph and perilymph meet
there is a ridge of epithelial cells along the whole length of the
basilar membrane
–> hair cells (for transduction)
–> support cells
Hair cells in the ear
cilia
receive info
hair cells transform mechanical energy into membrane depolarization or hyperpolarization
when stereocilia bend, they cause the tip links to open/close gated ion channels
ion channels mostly allow for Ca2+ or K+ flow
Tips of cilia/hair cells are embedded in the
tectorial membrane
-tectorial perturbation moves cilia
Trp, mechanically gated channels, pass K+ IN
Trp channel opens, K+ In depolarizes, spits out NT (glutamate) onto the primary neuron in response to depolarization
how do we detect different sound frequencies/pitch
different frequency sounds cause vibration of different regions of the basillar membrane
- code for differences in pitch
ex. labelled line coding from basillar membrane allows brain to interpret the diff inputs as diff frequencies/pitch
does sound go to both sides of the brain
yes!
sound is processed so that information from each ear goes to both sides of the brain
