Download DB12 synaptic transmission

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
Perfuse heart B
 Heart B slows


chemical = vagusstoff ~
-
A
B

Repeat w/ accelerator nerve
 HR increases
 Acceleransstoff ~
+
A
B
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 ~

Synaptic Transmission Model
1.
2.
3.
4.
5.
6.
Precursor transport
NT synthesis
Storage
Release
Activation
Termination ~
Presynaptic
Axon Terminal
Terminal
Button
Postsynaptic
Membrane
Dendritic
Spine
1. Precursor
Transport
2. Synthesis
Enzymes & cofactors ~
E
3. Storage
E
3. Storage
In vesicles
Terminal
Button
Dendritic
Spine
Synapse
4. Release
diffusion
AP
Ca++
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 ~
