Synaptic Transmission Lecture 12. Synapses n Communication b/n neurons n Electrical l Electrotonic...
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Transcript of Synaptic Transmission Lecture 12. Synapses n Communication b/n neurons n Electrical l Electrotonic...
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Synaptic Transmission
Lecture 12
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Synapses
Communication b/n neurons Electrical
Electrotonic conduction Chemical
Ligand / receptor ~
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Electrical Synapses
Tight jucnctions Connexons Passive current & larger molecules (e.g., ATP)
Synchronous activity Breathing Hormone release from
hypothalamus ~
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Synaptic Transmission
Nature of signal across synapse?
Sherrington electrotonic
transmission Most neural
conduction too slow Delay in spinal
reflexes ~
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Synaptic Transmission
Otto Loewi had a dream Chemical Signal? How can it be
demonstrated? Frog Heart
Preparation ~
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Stimulate Vagus Heart rate slows ~
electrical stimulation
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Stimulate A Collect fluid ~
A B-
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A B
Perfuse heart B Heart B slows
chemical = vagusstoff ~
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B
Repeat w/ accelerator nerve HR increases Acceleransstoff ~
A+
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The Chase Is On
Search for chemical neurotransmitters (NT)
Criteria Synaptic Model ~
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Synaptic Events
Action Potential reaches axon terminal Chemical substance released
Neurotransmitter (NT) Diffuses across synapse Binds to receptor protein
EPSP or IPSP ~
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1. Precursor transport
2. NT synthesis
3. Storage
4. Release
5. Activation
6. Termination ~
Synaptic Transmission Model
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PresynapticAxon Terminal
PostsynapticMembrane
Terminal Button
Dendritic Spine
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1. Precursor Transport
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E
2. Synthesis
Enzymes & cofactors ~
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3. Storage
E
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Synapse
Terminal Button Dendritic
Spine
3. StorageIn vesicles
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Ca++
4. Release
diffusion
AP
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5. Activation NT binds to receptor
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Activation
NT binds to postsynaptic receptor opens ion channel EPSP
Na+ into cell or IPSP
K+ out of cell ~
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6. Termination
4 Basic methods Diffusion Enzymatic degradation Presynaptic reuptake
active transport Autoreceptors ~
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6. Termination autoreceptors
A
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Autoreceptors
On presynaptic terminal Binds NT
same as postsynaptic receptors different receptor subtype
Decreases NT release & synthesis ~
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Termination
Must have discrete signal What if ion channels continually open?
ions move toward equilibrium membrane no longer polarized no EPSPs or IPSPs
Disrupts neural communication Termination ---> neuron repolarizes ~