Sensory Transduction

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 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 endingsSensory neurones

Classification based on physical stimulus

MechanoreceptorsThermoreceptorsPhotoreceptorsChemoreceptors




.. Common to all types of sensory receptors

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




.. Common to all types of sensory receptorsThe 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 codingEnsemble 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




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 systemReceptor cellsMitral cellsPeriglomerularcellsGranule cells




Olfactory receptor




Olfactory receptorOdorant binding protein

Odorant receptor (onetype for each cell)

Olfactory G-protein

Increase of cAMP

Opens Na+, K+, Ca2+ ch.

Cell depolarisation




Olfactory pathway




Gustatory system

SweetSaltySourBitterUmami




Tongue

Tongue Papilla

Taste buds




Taste buds




Taste receptor

G-protein coupled receptor

Ion channels

SweetBitterUmami

SaltySour




Taste receptor




Taste receptor

Receptor bindingG-proteinSecond messengersOpening of TRPM5Depolarisation




Taste receptor

Na+ enter cellDepolarisation

Low pH opens H+ ch.H+ enter cellDepolarisation




Taste receptor

DepolarisationCa2+ channels openCa2+ causesneurotransmitterrelease

ATP




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

rhodopsin




Rhodopsin cycle

rhodopsin

scotopsin

all-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 -40mVLight produces metarhodopsin II

Resting potential drops to as lowas -70mV

glutamateGlutamate 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

glutamate




Vestibular systemSemicircular canals




Somatosensory system




Somatosensory system

MechanoreceptorsThermoreceptorsNociceptors




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

VisualAuditory

Documents

Sensory Transduction