I need help to see exactly what is going on here. According to the textbook here is shown a synapse, but I cannot quite see the things the textbook says are there.

From what I understand: (1) At1 and At2 are axons?, (2), The black thing on the bottom left is a dendrite?, (3) s1 and s2 are post-synaptic densities?

Is there more to see here that I am missing?

enter image description here

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    $\begingroup$ The word is "synapse" not "synapsis" - and yes, those are the major features to see. Note that is probably more correct to say those are axon terminals, hence the "at". All the spherical objects inside the axon terminals are vesicles. I think this question should probably be closed, though, because you don't have much of a question: the textbook is telling you what's in the picture. $\endgroup$
    – Bryan Krause
    Commented May 10, 2017 at 20:32
  • $\begingroup$ Does the book have another diagram or picture of a synapse from a different angle? Or a picture that shows synapses within a larger context? Would be worth adding to this post if so. $\endgroup$
    – lauir
    Commented May 11, 2017 at 1:41

1 Answer 1


You can tell that the structures labelled At are axons, or rather axon terminals, due to the presence of the synaptic vesicles.

I think this is a fine photo that's a bit more a clear representation: enter image description here


PSDs are really just protein aggregates that are thought to facilitate neurotransmitter trafficking. So the structures here make sense. At least, they make sense if you know the tissue you're running in TEM, and you understand that how you cut the samples for microscopy affect the way they end up looking. My only assumption that Den is a dendrite is knowing that axon terminals synapse with other dendrites: they're receiving structures. I'm also somewhat sure the cell body from which the dendrites extend have that characteristically large nucleus.

The other understanding is that these pictures are just snippets of a larger image and you only get used to identifying structures through practice and experience. Rather, the author wants you to see this section and for lack of context has identified the structures for you.


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