Synapse

What is it? A junction/gap between two or more neurons.
General idea-neurotransmitter molecules that are released, diffused across the gap to set up another action potential in the next neuron.
[ANNOTATED DIAGRAM ABOVE]
Key terms:
- post-synaptic membrane
-ion channel
-threshold level
-facilitation
-inactivation
-re-synthesized
-neurotransmitters
-action potential
-calcium ion channel
-vesicle
-pre-synaptic membrane

Synapses in more detail...
A synapse is basically a junction. It is a fluid filled gap that separates the plasma membranes of the two (or more) neurons.
1) A nerve impulse reaches the axon terminus (the end of the axon) and is sent across the gap by chemical molecules called neurotransmitters. (there are over 30 types of these molecules, neurotransmitters is a general term)
2) the nerve impulse causes Ca2+ ions to diffuse through channels INTO the synaptic knob.
3) The influx rushing in of calcium causes the vesicles that contain the neurotransmitters to fuse with the pre-synaptic membrane.
4) Neurotransmiter is released into the synaptic cleft-space between the pre and post synaptic membrane. By a process called exocytosis (the fusion of vesicles leading to the released of materials OUTSIDE the cell)
5) the neurotransmitters diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane.
6) the binding action causes ion channels to open and ions diffuse DOWN their concentration gradient.
7) this causes local depolarization and this leads to an impulse (action potential) being generated in the post-synaptic neuron.
8) the neurotransmitter diffuses back towards the pre-synaptic cell and it can either be taken back into the synaptic knob to be recycled, or it can be degraded or simply diffuses out of the synapse.

REFERENCE: 
Text: Biology course companion, Andrew Allot and David Mindorff, page 245
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