Synaptic transmission

1
Synaptic transmission

• Communication between neurons and other body
  cells Other neurons, glands, and muscles

2
Chemical communication

• Neurotransmitters
• Neuromodulators and ectopic synapses
• Hormones
• Pheromones

3
Structure of the synapse

• Terminal button and presynaptic membrane
• Synaptic vesicles small and large
• Synaptic gap
• Post-synaptic membrane and receptor sites/
  receptor density
• Autoreceptors

4
Synaptic transmission
5
The process Presynaptic

• Preparation Docked vesicles
• Arrival of the action potential
• Opening of voltage-dependent calcium channels
• Separation of docking proteins opens fusion pore
• W figures

6
The process Postsynaptic

• Momentary affinity and binding
• Neurotransmitter-dependent ion channels
• A. Ionotropic receptors
• B. Metabotropic receptors
• 1. G-proteins a subunit to ion channels
• 2. G-proteins a subunit to second messengers
• cAMP, cGMP to
• a. ion channels, or
• b. nucleus

7
Postsynaptic potentials

• EPSP
• Na channels open, Na enters
• If Cl- channels open, Na EPSP is limited
• Ca2 channels open, Ca2 enters
• This affects not only the EPSP, but also binds
  with proteins to activate enzymes
• IPSP
• K channels open, K leaves
• Cl- channels open

8
Summation

• Temporal summation
• Spatial summation
• Graded potentials
• Cable conduction

9
Stopping the process

• Reuptake
• From cleft by transporters to sending cell
• Assisted by glial cells?
• Second step Re-storing in vesicles
• Enzyme action
• Acetylcholine esterase (AChE) in cleft
• MAO and COMT are inside terminal button, so are
  not involved in stopping transmission

10
Axoaxonic synapses

• Presynaptic inhibition
• Presynaptic facilitation
• Dendrodendritic synapses
• Chemical
• Ionic (Gap junctions)
• Retrograde synapses
• CO and NO feedback from postsynaptic cell to
  presynaptic cell Agonistic effect

11
Other chemical communication

• Neuromodulators
• Hormones
• Peptides act on metabotropic receptors with
  second messengers
• Steroids
• act on receptors in the nucleus
• act on synapses, with a rapid effect on synaptic
  transmission