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Synaptic Transmission
Lecture 12
Synapses
Communication b/n neurons Electrical
Electrotonic conduction Chemical
Ligand / receptor ~
Electrical Synapses
Tight jucnctions Connexons Passive current & larger molecules (e.g., ATP)
Synchronous activity Breathing Hormone release from
hypothalamus ~
Synaptic Transmission
Nature of signal across synapse?
Sherrington electrotonic
transmission Most neural
conduction too slow Delay in spinal
reflexes ~
Synaptic Transmission
Otto Loewi had a dream Chemical Signal? How can it be
demonstrated? Frog Heart
Preparation ~
Stimulate Vagus Heart rate slows ~
electrical stimulation
-
Stimulate A Collect fluid ~
A B-
A B
Perfuse heart B Heart B slows
chemical = vagusstoff ~
-
B
Repeat w/ accelerator nerve HR increases Acceleransstoff ~
A+
The Chase Is On
Search for chemical neurotransmitters (NT)
Criteria Synaptic Model ~
Synaptic Events
Action Potential reaches axon terminal Chemical substance released
Neurotransmitter (NT) Diffuses across synapse Binds to receptor protein
EPSP or IPSP ~
1. Precursor transport
2. NT synthesis
3. Storage
4. Release
5. Activation
6. Termination ~
Synaptic Transmission Model
PresynapticAxon Terminal
PostsynapticMembrane
Terminal Button
Dendritic Spine
1. Precursor Transport
E
2. Synthesis
Enzymes & cofactors ~
3. Storage
E
Synapse
Terminal Button Dendritic
Spine
3. StorageIn vesicles
Ca++
4. Release
diffusion
AP
5. Activation NT binds to receptor
Activation
NT binds to postsynaptic receptor opens ion channel EPSP
Na+ into cell or IPSP
K+ out of cell ~
6. Termination
4 Basic methods Diffusion Enzymatic degradation Presynaptic reuptake
active transport Autoreceptors ~
6. Termination autoreceptors
A
Autoreceptors
On presynaptic terminal Binds NT
same as postsynaptic receptors different receptor subtype
Decreases NT release & synthesis ~
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 ~