This image shows a 3D view of an excitatory synapse between cultured hippocampal neurons revealed by cryo-electron tomography. Segmented structures are rendered as colored surfaces to facilitate visualization of synaptic structures, including presynaptic (light yellow) and postsynaptic (cyan) membranes, ER and endosomes (orange), mitochondrion (outer: gold and light pink), microtubules (yellow), ribosomes (cyan), actin filaments (red), putative presynaptic (magenta) and postsynaptic (yellow) adhesion molecules, putative glutamate receptors (red), postsynaptic density filaments either attached to (blue) or away from (purple) the postsynaptic membrane, as well as dense core vesicles (purple) and synaptic vesicles of various sizes. For more information, see the article by Tao et al. (pages 1493–1510).