Department of Physiology, 2 nd Faculty of Medicine, Charles University Copyright © 2011 Luděk...

Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad

Sensory Sensory transductiontransduction

NeurophysiologyNeurophysiologypage 1page 1




Reception, perception, and transmission of information

Our actions arebased on whatwe perceive, i.e. the brain can ”read” it.

The brain createssubj. experience




How neurones communicate

Action potentialAction potential




Action potential

Voltage-gatedNa+ and K+

ion channels

Na+ Na+

K+ K+




Postsynapticpotentials

Neurotransmissionat a chemicalsynapse

Source ofexcitation isanother neurone




Reception




Stimulus processing and information coding




Sensory receptors

Anatomical classification

Nerve endings

Sensory neurones

Classification based on physical stimulus

Mechanoreceptors

Thermoreceptors

Photoreceptors

Chemoreceptors




.. Common to all types of sensory receptors

Change of membrane potential-> Generation of receptor (“generator”) potential

Similar to postsynaptic potentials-> Threshold for action potential must be crossed

Receptor potentialis graded, i.e., itis proportional tostimulus strength

Receptor potentialsdecrease with distance





The number of action potentials per time unitis linearly proportional to the receptor potential

Receptor potential [mV]





The number of action potentials per time unitis linearly proportional to the receptor potential





Receptor membrane becomes permeablefor all small ions (however Na+ prevail)

Receptor membrane is not electrically excitable

Action potentials are generated down the line(even in different neurones, such as in vision)





Summation ofreceptor potentialsin time

Summation ofreceptor potentialsin space




Adaptation

Decrease in amplitude of the generator potentialduring a prolonged sustained stimulation

Stimulation Stimulation




Coding

All-or-none (binary)

Frequency vs. interval coding

Ensemble coding (a combination of morereceptors codes for a single feature)

Non-spiking coding (cells in the retina)

There are 10 kinds of people: Those whoUnderstand binary and those who don’t.

10 means 1x21 + 0x20 = 2

There are 10 kinds of people: Those whoUnderstand binary and those who don’t.

10 means 1x21 + 0x20 = 2




Sensory systems

Visual system

Auditory system

Vestibular system

Olfactory system

Gustatory system

Somatosensory s.




Olfactory system




Olfactory system

Lamprey Shark Frog




Olfactory system




Olfactory system




Olfactory system

Receptor cells

Mitral cells

Periglomerularcells

Granule cells




Olfactory receptor




Olfactory receptorOdorant binding proteinOdorant binding protein

Odorant receptor (onetype for each cell)Odorant receptor (onetype for each cell)

Olfactory G-proteinOlfactory G-protein

Increase of cAMPIncrease of cAMP

Opens Na+, K+, Ca2+ ch.Opens Na+, K+, Ca2+ ch.

Cell depolarisationCell depolarisation




Olfactory pathway




Gustatory system

SweetSaltySourBitterUmami




Tongue

TongueTongue PapillaPapilla

Taste budsTaste buds




Taste buds




Taste receptor

G-protein coupled receptor

Ion channels

Sweet

Bitter

Umami

Salty

Sour




Taste receptor




Taste receptor

Receptor binding

G-protein

Second messengers

Opening of TRPM5

Depolarisation




Taste receptor

Na+ enter cell

Depolarisation

Low pH opens H+ ch.

H+ enter cell

Depolarisation




Taste receptor

Depolarisation

Ca2+ channels open

Ca2+ causesneurotransmitterrelease

ATPATP




Gustatory pathway




Visual system




Retina




Rods and cones - photoreceptors




Retinal cells

Rods

Cones

Bipolar cells

Ganglion cells

Horizontal cells

Amacrine cells




Photo-transduction in rods

rhodopsinrhodopsin




Rhodopsin cycle

rhodopsinrhodopsin

scotopsinscotopsin

all-trans retinalall-trans retinal

Metarhodopsin IItriggers cellhyperpolarisation




Rod receptor potential

Metarhodopsin II reducesinward flow of Na+ in outersegment

In the dark, the outer segmentsuffers from the leakage of Na+

This reduces resting potentialto -40mV

Light produces metarhodopsin II

Resting potential drops to as lowas -70mV

glutamateglutamateGlutamate release is reduced




Action potentials in the retina

The only type of retinal cell thatgenerates action potentials areganglion cells

Other cells conduct signals bysimple electric conduction

Retinal ganglion cells produceaction potentials repeatedly(40 Hz), even if not stimulated.

Visual signal is formed by ‘extra’action potentials.




Auditory and vestibular system




Auditory and vestibular system




Organ of Corti




Organ of Corti




Stereocilia

glutamateglutamate




Vestibular system

Semicircular canals




Somatosensory system




Somatosensory system

Mechanoreceptors

Thermoreceptors

Nociceptors




Somatosensory receptors

Ruffini’s corpuscle – pressure sensor

Merkel’s cells – pressure receptor

Meissner’s corpuscle – light touch

Hair follicle receptor – analog. to Meissner’s c.

Pacinian corpuscle – fast-adapting pressure sensor

Cold and warmth sensors

Pain sensor – free nerve ending




Pain receptors

Nerve endingsNon-adapting


SummarySummaryNeurophysiologyNeurophysiologypage 1page 1

Sensory transduction in general

Specific sensory systems

Receptor neurones

Receptor potential

Olfactory

Gustatory

Visual

Auditory

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