lecture 14- chemoreception and auditory system, sensory II Flashcards by Maya Lima

Sensory receptor in olfactory system

= olfactory neuron (primary neuron)

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What is olfaction

smell

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olfactory cilia (dendrites) contain

odorant receptor proteins
and they project downwards into the mucous layer

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axons project upwards though the —- in olfactory neurons

lamina propria and bone

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the olfactory neurons synapse with the

secondary sensory neurons in the olfactory bulb

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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

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what carries info to the olfactory bulb?

olfactory neuron axons (cranial nerve I)

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the basal cell layer includes —- that replace olfactory neurons

stem cells

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what must dissolve in the mucous layer?

odorant molecules

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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

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humans have about —- different odorant receptors

400

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what are odorant receptors

GPCRs and they are all linked to specialized G proteins

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each neuron expresses —- type of odorant receptor

only 1

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combinations of activated receptors and neurons allow us to smell —– odors

about 5000

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a perceived odor may involve a combination of —–

types of odorant receptors

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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

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explain why the olfactory system is linked with the limbic system and cerebral cortex

smell is linked with emotion and memory

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does the olfactory pathway go through the thalamus?

NO!! the olfactory pathway bypasses the thalamus

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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

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gustatory system

taste

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each taste bud= — taste cells

50-150

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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

1. ligands activate the taste cell 2. various intracellular pathways are activates 3. Ca2+ signal in the cytoplasm triggers exocytosis or ATP formation 4. NT or ATP is released 5. 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

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