Summary
The ultrastructure of synapses from the nervous systems of seven species of ctenophores has been studied. All synaptic contacts so far observed show a peculiar organization characteristic of this phylum: the pre-synaptic neurite contains in sequence from the plasma membrane: a row of vesicles lining the synaptic membrane, a sac of endoplasmic reticulum which is connected with the rough reticulum of the neuron, and one or several mitochondria. The arrangement of these closely associated organelles is constant, forming a complex referred to as thepre-synaptic triad.
The pre-synaptic triad is found both in interneural synapses—which may be polarized, symmetrical or reciprocal — and in various neuro-receptor and neuro-effector junctions.
The possible functional implications of these features are discussed.
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Hernandez-Nicaise, ML. The nervous system of ctenophores III. Ultrastructure of synapses. J Neurocytol 2, 249–263 (1973). https://doi.org/10.1007/BF01104029
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DOI: https://doi.org/10.1007/BF01104029