Lec 14 Flashcards by Mahan Tavakolian

Olfactory system

Uses free nerve ending

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From air to brain

Olfactory neuron—cilia(dendrite) receptors
Olfactory bulb— synapses are find
Olfactory tract—#2 neuron axon goes to olfactory cortex

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Bone between nose and brain

Ethmoid Bone

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Cilia(dendrite like)

Cilia project downward into mucous layer
Cilia have odorant receptor proteins GPCRS

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Supporting cell

1- stem cell
2- can replace olfactory sensory neurons

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Mucous layer

-Odorant must dissolve into this layer
-Odorant must bind to specific odorant receptors(GPCR)

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How many different Odorant receptor in human?

400 different odorant receptors
ALL ARE GPCRS
combination of activated receptors and neurons allow us to smell 5000 odors

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Signal transduction in olfactory

1-Odor bind to G protein-coupled receptor
2-Activated G protein activate adenylyl cyclase
3-Adenylyl cyclase convert ATP to cAMP(secondary messenger)
4-cAMP open cyclic-nucleotide gated Na channels
5-Sufficient Receptor potential
6-Produce AP at axon hillock

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Specialized G protein for olfactory tranduction

Golf

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Olfactory sensory pathway

1- olfactory neurons
2- cranial nerve I
3- olfactory bulb
4- olfactory tract
5- olfactory cortex
6.1- limbic system
6.2- cerebral cortex

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Olfactory connection with limbic system

Smell is linked to emotion and memory

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——— are similar and hand to hand with olfactory

Taste sensors

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Each taste buds is ——— taste cells

50-150

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Taste cells are

Non-neural

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Each taste cell is

Sensitive to particular tastant ligand
Polarized:
—receptor at apical membrane
—1 sensory neuron communication at basal membrane

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Intracellular signaling pathway is ——— for each taste cell

Different

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Different tastes

Sweet
Umami
Bitter
sour
*different GOCR for each one

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Type I support cells

May sense salt when Na enters channel
ENAC

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Receptor cells (type II)

Sweet/umami/bitter
Release ATP as messenger

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Presynaptic cell (III)

Feels sour
Activate by H(+)
Release serotonin as messanger

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Primary sensory neurons

Two different kind
—Sensitive to ATP
—Sensitive to serotonin

Type II pathway

Different GOCR for each taste
Release if Calcium ion
Calcium triggers ATP release

Type III pathway

Ph drop
H(+) enters the cell
Ca rushes in from ECF
Serotonin production

What is sound

Sound is perception and interpretation of air waves

Pressure wave

Sinusoidally varying density of air molecules

Volume/Loudness

Amplitude of a sound wave Measured in dB

Pitch

Frequency of sound wave Measured in Hz

External ear

**pinna** :direct sound waves into ear Ear canal: air filled space

Boundary of external and middle ear

Tympanic membrane

Drum vibrate Convert sound wave to mechanical stress

Middle ear

Air filled space **bones from external to internal** Malleus Incus Stapes

Boundary middle and inner ear

Oval window Round window **separate air field from fluid field** Convert mechanical energy to fluid wave energy

Inner ear

Fluid filled Cochlea + nerves

Cochlea function

Balance Hearing Equilibrium

How AP fires?

1- fluid wave created in cochlea by oval window 2- fluid waves push on cochlear duct membrane 3- hair cells bend and ion channels open 4-create electrical signals 5- release neurotransmitters 6- neurotransmitters on sensory cell create AP

Ap travel from sensory neuron to brain by

Cochlear duct

Energy wave moves from ———

cochlear duct to tympanic duct and go back to middle ear from round window

Cochlear duct name

Endolymph **high in K**

Vestibular and tympanic duct name

Perilymph **connected together **

Organ of corti function

Signal transduction Graded potential

Endolymph composition is similar to

ICF

How hair cells release neurotransmitters

1- Basilar membrane on bottom 2- Ridge of epithelial cell above that(support cells + hair cells) 3- Cilia of hair cells embedded in tactorial membrane 4- fluid wave move tactorial membrane which moves cilia 5- cilia is mechanically gated channels Which will open by tactorial movement 6-opening cause release of neurotransmitters

Tip link

Cilias are connected together by tip link Which if you pull on cilia, all cilia will move

Which ion flow when mechanically gated channels open on sterocilia

Ca and K

Excitation and inhibition of cilia cells

When hair cells bend in one direction, cell depolarizes, which increase AP frequency When hair cells bend in opposite direction, ion channel close and cell hyperpolarize

Sterocilia excitation will produce

Receptor potential which is made by K go inside the cell

as basilar membrane moves further from oval window, it gets

Wider, thinner, more flexible Which increase the sensitivity to low frequencies

Regional differences

High frequency is sensed in closer distance to oval window Lower frequency further from oval window

Labeled line coding from basilar membrane

Different pathway Different input Different frequencies Brain can differentiate

Auditory pathway

Sound waves goes to 1- cochlea (left/right) 2- brainstem **cross over happens** 3- thalamus 4- auditory cortex (left/right)