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Synaptic Transmission. Lesson 12. Synapses. Communication b/n neurons Electrical Electrotonic conduction Chemical Ligand / receptor ~. Electrical Synapses. Tight junctions Connexons Passive current & larger molecules (e.g., ATP) Synchronous activity Breathing

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synapses
Synapses
  • Communication b/n neurons
  • Electrical
    • Electrotonic conduction
  • Chemical
    • Ligand / receptor ~
electrical synapses
Electrical Synapses
  • Tight junctions
    • Connexons
    • Passive current
    • & larger molecules (e.g., ATP)
  • Synchronous activity
    • Breathing
    • Hormone release from hypothalamus ~
synaptic events
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
Synaptic Transmission Model

1. Precursor transport

2. NT synthesis

3. Storage

4. Release

5. Activation

6. Termination ~

slide6

Postsynaptic

Membrane

Presynaptic

Axon Terminal

Dendritic

Spine

Terminal

Button

slide7

1. Precursor

Transport

slide8

2. Synthesis

Enzymes & cofactors ~

E

slide10

3. Storage

In vesicles

Terminal

Button

Dendritic

Spine

Synapse

slide11

AP

Ca++

4. Release

  • via exocytosis
  • diffusion

Synapse

exocytosis membrane fusion
Exocytosis: Membrane Fusion
  • Ca2+ influx
    • 2d messenger
    • Ca2+ -Calmodulin
  • SNAPs
    • soluble-NSF-attachment proteins
  • SNAREs
    • SNAP receptors ~
slide13

5. Activation

  • NT binds to receptor
activation
Activation
  • NT binds to postsynaptic receptor
    • opens ion channel
    • EPSP
      • Na+ into cell
    • or IPSP
      • K+ out of cell ~
6 termination
6. Termination
  • 4 Basic methods
    • Diffusion
    • Enzymatic degradation
    • Presynaptic reuptake
      • active transport
    • Autoreceptors ~
slide16

6. Termination

  • autoreceptors

A

autoreceptors
Autoreceptors
  • On presynaptic terminal
  • Binds NT
    • same as postsynaptic receptors
    • different receptor subtype
  • Decreases NT release & synthesis ~
termination
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 ~
axoaxonic synapses
Axoaxonic Synapses
  • Modulation of NT release
    • *via  or  Ca2+ influx
  • Presynaptic Facilitation
    • Increases NT release
  • Presynaptic Inhibition
    • decreases NT release
  • Via modulation of Em
    • Ca2+, K+, and Cl- ~
drug interaction terms
Drug Interaction Terms
  • Drug’s effect on synaptic transmission
    • Direct  at postsynaptic receptor
    • Indirect  at any other step
  • Agonist (AG)
    • mimics or ­NT effects
  • Antagonist (ANT)
    • blocks or ¯NT effects ~