Nerve synapse. Artwork of the junction between two nerve cells. The junction between a nerve cell and another cell is called a synapse and this is where chemicals known as neurotransmitters (red spheres) cross the gap to affect the postsynaptic cell. The incoming nerve impulse (from left) causes release of the neurotransmitter, which crosses the gap and binds to receptors (pink) on the receiving nerve cell. This causes the receptors to open and act as ion channels (orange) through which ions (green spheres) flow in and out of the cell, causing the outgoing nerve impulse. Drugs (blue triangles) can bind to receptors to affect nerves. Mitochondria (green tubes) produce energy within cells.