[Functional restructuring of the ultrastructure of the giant neuron (Retzius') in the medicinal leech and the possible role of Ca++ ions in these processes].

As it has been demonstrated in the giant (Retzius') neuron of the leech (Hirudo medicinalis), at the synaptic activation for 5 sec. and 10 min., ultrastructural changes in the neuron are accompanied with an increasing number of Ca++ ions in hyaloplasm, mitochondria and cytosomes. After activation, the ultrastructural changes increase, and the number of Ca++ ions returns to the initial level. A suggestion is made on a trigger function of Ca++ ions when the neuronal ultrastructure changes under conditions of the synaptic activation.