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

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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+

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

Lamprey Shark Frog

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

Bitter

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

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

Organ of Corti

Stereocilia

glutamateglutamate

Vestibular system

Semicircular canals

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

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

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