User:Jtwsaddress42/Projects/Project 3/Sections/Chapter 4/The Origin Of The Pre & Post Synaptic Clefts - Neuroid Conduction & The Nematocyst

While the synapse appears to be one of the defining features of a neuron, it actually requires two cell to form a synapse. This is the point at which release and reception of "neurotransmitter" between contacting cells takes place in a localized fashion on the pre- and post-cell membrane on either side of the intervening gap.

Cells have a long history of chemical and mechanical communication. What distinguishes neurotransmission from other types of chemical communication between cells is the discretely localized transmission across the synaptic gap which occurs between two contacting cells.

It is important to remember that the evolutionary emergence of the synapse is a co-evolutionary process involving two cells and the pre- and post- synaptic side of the synapse.

The evolutionary and developmental, question is, "how did the receptors for these ancient substances came to be localized on the cell membrane of neuroid tissue cells to eventually emerge as the synaptic cleft. This transition appears to have occurred at the origin of the Cnidarian phyla when the first neurons and nervous system emerged in the form of a radial nerve net.

Cavalier-Smith suggests that there is a pathway from the flask cells of sponges to cnidarian predatory feeding behaviors that will eventually lead to the emergence of the synapse:

In this scenario, the pre-synaptic cleft evolved as an effector organ in neuroid tissues for predatory feeding in pre-neural cnidarian ancestors employing the neuroid tissues to effect the global discharge of the nematocysts in a concerted fashion - the nematocysts being recently differentiated from the peripheral neuroid cells within the neuroid tissue population. The nematocysts occupies the post-synaptic side of the synaptic cleft - and, drives the evolutionary emergence of the pre-synaptic cleft and the emergence of the neurons and glia as the ancestral neuroid tissue evolves into nervous tissue.