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  • Action potentials occur between neurons and result in communication via neurotransmitters 

    • There are a variety of important structures involved in this process

      • Presynaptic membrane: membrane of a terminal button on the presynaptic neuron that lies adjacent to the cleft; releases neurotransmitters from vesicles to the postsynaptic neuron from the release zone

      • Synaptic vesicle: a small bead like structure that contains neurotransmitter molecules  

      • Synaptic cleft: space between neurons across which neurotransmitters are released 

      • Postsynaptic membrane: cell membrane opposite the terminal buttons of the presynaptic neuron; receives the message in the form of neurotransmitters 

    • This occurs in stages 

  1. Action potentials result in the release of neurotransmitters via synaptic vesicles (small, hollow, beadlike containers) at the presynaptic membrane terminal buttons in the release zone as a result of intense depolarization from Ca2+ influx into the ion (reaching of the threshold of activation); release made possible for vesicles by VAMPS like vSNARE (neurexin) and tSNARE (syntaxin); some toxins can disturb this process (neurotransmitters not released; ex. Botulinum/botox) 

  1. Merge and recycle: vesicle merges with membrane and then buds off (endosomes); most common

  2. Kiss and leave: vesicle docks then leaves

  3. Kiss and stay: vesicle docks and stays

  4. Neurotransmitters cross the synaptic cleft 

  5. Neurotransmitters are received by the postsynaptic membrane 

  • Neurotransmitter signaling can be stopped in a variety of ways 

  1. Diffusion: after release, diffuses out

  • Slow, inefficient, little control 

  1. Internalization: receptors are sucked into postsynaptic membrane for a short period of time after activation; not fast, but allows for reuse

  • Usually caused by agonists

  1. Reuptake: Neurotransmitters taken back into the presynaptic membrane 

  • Fast, efficient

  • Glial cells also assist in reuptake (astrocytes, phagocytes) 

  1. Enzymatic Degradation: degrade the released neurotransmitter to the point of dysfunction by breaking it into its subunits for recycling 

  • Fastest, through not efficient (must make neurotransmitters again)