Synapses

• What is a synapse?

  A junction between neurons where action potential is transmitted.

  
• What are the two types of synapses?

  Electronic (electrical) and chemical.

  
• What connects cells in electronic synapses?

  Gap junctions.

  
• What do gap junctions allow?

  Direct transfer of ionic current.
• What proteins form gap junctions?

  Connexins.
• What is the main type of synapse in the CNS?

  Chemical synapse.

  
• How wide is the synaptic cleft?

  Approximately 50 nm wide.
• What do presynaptic terminals contain?

  Synaptic vesicles.

  
• What do postsynaptic membranes contain?

  Receptors for neurotransmitters.
• What are the criteria that define a neurotransmitter?

  1. Present in the presynaptic terminal.
  2. Released in response to presynaptic depolarization and Ca2+ dependent.
  3. Specific receptors must be present on the postsynaptic cell.
• What can happen to neurotransmitters after release?

  They may diffuse away, be taken up by transporters, or be broken down by enzymes.
• What is the effect of excitatory neurotransmitters on neurons?

  They cause depolarization, moving the membrane potential towards threshold.
• What is an example of an excitatory neurotransmitter?

  Glutamate.

  
• What type of receptor does glutamate bind to?

  NMDA subtype receptor.
• What is the main inhibitory neurotransmitter in the brain?

  Gamma amino butyric acid (GABA).
• What is the effect of GABA on the membrane?

  It causes hyperpolarization of the membrane.
• What neurotransmitter is released at the neuromuscular junction?

  Acetylcholine (ACh).

  
• How is acetylcholine synthesized?

  From AcetylCoA and choline in the presynaptic terminal.

  
• What happens to acetylcholine after it is released?

  It is broken down by acetylcholine esterase.

  
• What is the role of depolarization in muscle contraction?

  It activates calcium channels that cause muscle contraction.
• What are the integrative features of transmitter action?

  • Summation
  • Temporal and spatial summation
  • Convergence
  • Divergence
• What is the effect of botulinum toxin on neurotransmitter release?

  It blocks vesicle docking at the membrane.
• What is the effect of neostigmine on acetylcholine?

  It blocks acetylcholinesterase, prolonging acetylcholine action.
• What is myasthenia gravis?

  An autoimmune disease where antibodies are produced against ACh receptors.
• What therapeutic use does neostigmine have?

  It can be used to treat myasthenia gravis.

  
• What is one criterion for a substance to be classified as a neurotransmitter?

  The neurotransmitter must be within vesicles in the presynaptic terminal
• What is another criterion for a substance to be classified as a neurotransmitter?

  The neurotransmitter must be Ca$^{2+}$ dependent and released by depolarization
• What is a third criterion for a substance to be classified as a neurotransmitter?

  The neurotransmitter must have receptors on the postsynaptic terminal
• What happens to a neurotransmitter after it is released into the synapse?

  • It can be broken down by enzymes
  • It can diffuse away from the synapse
  • It can be picked up by specific transporters
• What is an excitatory neurotransmitter?

  It’s a neurotransmitter that brings the Em of the membrane of postsynaptic closer to threshold
• What effect does an excitatory neurotransmitter have on the postsynaptic membrane?

  It leads to depolarization