sensory transduction
TRANSCRIPT
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
NeurophysiologyNeurophysiologypage 1page 1
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
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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How neurones communicate
Action potential
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Action potential
Voltage-gatedNa+ and K+
ion channels
Na+ Na+
K+ K+
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Postsynapticpotentials
Neurotransmissionat a chemicalsynapse
Source ofexcitation isanother neurone
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Reception
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Stimulus processing and information coding
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Sensory receptors
Anatomical classification
Nerve endingsSensory neurones
Classification based on physical stimulus
MechanoreceptorsThermoreceptorsPhotoreceptorsChemoreceptors
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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.. 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
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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.. Common to all types of sensory receptors
The number of action potentials per time unitis linearly proportional to the receptor potential
Receptor potential [mV]
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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.. Common to all types of sensory receptorsThe number of action potentials per time unitis linearly proportional to the receptor potential
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
NeurophysiologyNeurophysiologypage 1page 1
.. Common to all types of sensory receptors
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)
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
NeurophysiologyNeurophysiologypage 1page 1
.. Common to all types of sensory receptors
Summation ofreceptor potentialsin time
Summation ofreceptor potentialsin space
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Adaptation
Decrease in amplitude of the generator potentialduring a prolonged sustained stimulation
Stimulation Stimulation
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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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
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
NeurophysiologyNeurophysiologypage 1page 1
Sensory systems
Visual system
Auditory system
Vestibular system
Olfactory system
Gustatory system
Somatosensory s.
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory system
Lamprey Shark Frog
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory systemReceptor cellsMitral cellsPeriglomerularcellsGranule cells
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory receptor
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory receptorOdorant binding protein
Odorant receptor (onetype for each cell)
Olfactory G-protein
Increase of cAMP
Opens Na+, K+, Ca2+ ch.
Cell depolarisation
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Olfactory pathway
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Gustatory system
SweetSaltySourBitterUmami
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Tongue
Tongue Papilla
Taste buds
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Taste buds
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Taste receptor
G-protein coupled receptor
Ion channels
SweetBitterUmami
SaltySour
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Taste receptor
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Taste receptor
Receptor bindingG-proteinSecond messengersOpening of TRPM5Depolarisation
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Taste receptor
Na+ enter cellDepolarisation
Low pH opens H+ ch.H+ enter cellDepolarisation
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Taste receptor
DepolarisationCa2+ channels openCa2+ causesneurotransmitterrelease
ATP
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Gustatory pathway
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Visual system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Retina
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Rods and cones - photoreceptors
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Retinal cells
Rods
Cones
Bipolar cells
Ganglion cells
Horizontal cells
Amacrine cells
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Photo-transduction in rods
rhodopsin
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Rhodopsin cycle
rhodopsin
scotopsin
all-trans retinal
Metarhodopsin IItriggers cellhyperpolarisation
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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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
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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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.
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Auditory and vestibular system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Auditory and vestibular system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Organ of Corti
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Organ of Corti
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Stereocilia
glutamate
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
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Vestibular systemSemicircular canals
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Somatosensory system
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Somatosensory system
MechanoreceptorsThermoreceptorsNociceptors
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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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
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
Sensory Sensory transductiontransduction
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Pain receptors
Nerve endingsNon-adapting
Department of Physiology, 2nd Faculty of Medicine, Charles University Copyright © 2011 Luděk Nerad
SummarySummaryNeurophysiologyNeurophysiologypage 1page 1
Sensory transduction in general
Specific sensory systems
Receptor neurones
Receptor potential
Olfactory
Gustatory
VisualAuditory