announcements
DESCRIPTION
Announcements. Mid term room assignments posted to webpage. Lecture 01. A. Excitor. B. Inhibitor. Record voltage. Simple case:. Threshold. A. B. Vm. hyperpolarizing inhibitory IPSP. Depolarizing excitatory EPSP. Threshold. A+B=smaller. Vm. - PowerPoint PPT PresentationTRANSCRIPT
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Announcements• Mid term room assignments posted to
webpage
A – Ho S361 (Pavilion)
Hoang – Lischka S309
Lishingham - Ngui S143
Nguyen – Seguin S128
Sek – Zia H305
Lecture 02 S319
Lecture 01
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A. Excitor B. Inhibitor
Record voltage
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Simple case:
Vm
Threshold
Depolarizing excitatoryEPSP
hyperpolarizing inhibitoryIPSP
Vm
ThresholdBA
A+B=smaller
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How to get hyperpolarizing potential?
• Neurotransmitter receptor is permeable to an ion whose Eion is more negative than resting membrane potential
• usually Cl- or K+
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++ -80 mV
+60 mV
0 mV
Hyperpolarizing Synaptic Potential
K+
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More complex case:
Vm
Depolarizing excitatory Depolarizing
ThresholdBA
Threshold
Vm
A+B=smaller
inhibitory
Why???
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Reversal Potential
• Membrane potential at which there is no net synaptic current
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eg. Frog NMJ
Control resting membrane potential
Current source
stimulus
-100
-50
0
+25
Measuring Reversal Potential
Reversal potential
Record membrane potential
Stimulate nerve
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• Many neurotransmitter receptors are permeable to more than one ion– Non-selective
• The reversal potential depends on the equilibrium potential and permeability of each ion– It will usually be between the equilibrium
potential of the permeable ions
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eg. Acetylcholine channel
• Permeable to both K+ and Na+
• For Frog muscle:• EK = -90 mV
• ENa = +60 mV
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Vm=Erev
Erev>Vm>EK
VmEK
Na+
VmENa
K+
EK = -90 mV
Neurotransmitterreceptor
-90
ENa = +60 mV
-50
0
+25
Reversal potential
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How can depolarizing potential be inhibitory?
• Excitatory synapses have a reversal potential more positive than threshold
• Inhibitory synapses have a reversal potential more negative than threshold
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How can depolarizing potential be inhibitory?
Vm
ThresholdBA
Erev
Erev
Example: Cl- permeable receptorin a cell whose Vthresh >ECl- > Vm
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Inhibition
• Channels of inhibitory synapses ‘short-circuit’ excitatory synapses
• Because neurotransmitter channels will drive the membrane potential toward their reversal potential
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• Neurotransmitters and receptors
• Synaptic Integration
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Types of Receptors1. Ligand-gated ion channels
• Neurotransmitter binding to receptor opens an ion channel
• Directly changes the membrane potential of the postsynaptic cell
• Also known as ‘fast’ synaptic transmission
2. G-Protein Coupled Receptors• Transmitter binds to receptor which activates
intracellular molecules• Can directly or indirectly change the membrane
potential• Also known as ‘slow’ synaptic transmission
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Neurotransmitter Receptors
Ligand-gated ion channels
Acetylcholine(Nicotinic)
Excitatory
Glutamate(AMPA, NMDA)
Excitatory
Serotonin(5-HT3)
Excitatory
GABAA Inhibitory
Glycine Inhibitory
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Neurotransmitter Receptors
G-Protein coupled receptors
Acetylcholine(muscarinic)
Usually excitatory
Glutamate(metabotropic)
Variable effects
Serotonin(5-HT1-7)
Variable effects
GABABinhibitory
Same neurotransmitter, different receptors
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Activate intracellular molecules
Open or close ion channeldirect effect
G-protein coupled receptor
Regulate other cellular functionseg gene expression
GTPGDP
receptor
G-proteins
indirect effect
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What happens to neurotransmitter after it is secreted?
• Acetylcholine– Broken down by Acetylcholinesterase into
Choline and Acetate– Choline transported back into nerve terminal
and resynthesized into Acetylcholine
• Glutamate– Transported into glia or the nerve terminal
and converted to glutamine
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• Serotonin– A neurotransmitter used in the emotional
centres of the brain
– Prozac is a drug that inhibits the reuptake of serotonin
– Therefore, Prozac makes serotonin remain in synaptic cleft longer
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Synaptic Integration
The sum of all excitatory and inhibitory inputs to a cell.
1. Spatial Summation
2. Temporal Summation
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Spatial Summation• The addition of several inputs onto one
cellA B
B
A
A+B
B
A
A+B
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Temporal Summation
AStim once
Stim twice
Stim twice
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Synaptic Integration
Soma and dendritesSynaptic inputs Axon Hillock
Passive current flow
Above threshold?
Yes No
Action Potential Passive CurrentDecays to zero
Summation
Conducts down axon
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Summary
• Excitation and inhibition in relation to the reversal potential
• Fate of neurotransmitters after release
• Types of transmitters and their receptors
• Synaptic integration leading to action potentials