Synapse neurotransmitters, illustration. The junction between a nerve cell and another cell is called a synapse. This is where vesicles (spheres) of chemicals known as neurotransmitters cross the gap from an axon to trigger the other (postsynaptic) cell (upper right). The incoming nerve impulse releases the neurotransmitter, which crosses the gap and binds to receptors on the receiving nerve cell, allowing increased flow of ions such as calcium (Ca2+) and chlorine (Cl-). Here, the neurotransmitter glutamate is triggering an NMDA (N-methyl-D-aspartate) receptor (upper left), while a GABA (gamma-aminobutyric acid) receptor is being triggered at lower right. NMDA receptors play an important role in memory. GABA receptors play an important role in muscle excitation.