Figure 3. Model of the distribution of molecules that affect the generation of Ca²⁺ waves and sparks in a hippocampal pyramidal neuron.

The initiation of waves at branch points and the preference of events to occur at branch points suggest that inositol trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs) are concentrated at those sites. The propagation of waves to the soma and nucleus indicates that the receptors are located in those compartments. Metabotropic glutamate receptors (mGluRs) are located at the base of spines and at other extrasynaptic sites. The endoplasmic reticulum (ER) is continuous throughout the cell and connects to the nuclear membrane, but only invades some spines. Not all receptors are shown.