Synapse. Illustration of a synaptic knob (at left), the junction between two nerve cells. When an electrical impulse reaches the synapse, vesicles (round blue shapes, lower left) burst through the cell membrane (exocytosis). They then release chemicals called neurotransmitters (red spheres). These cross the synaptic cleft, the gap between the two cells. When they reach the receptor cell they will bind to the cell. There they will trigger an electrical impulse in the receptor cell. Information is transmitted along the nervous system in this manner. The green, cigar-shaped structures are mitochondria, the sites of energy production within the cell.