Serotonin nerve receptor. Animation of a molecule of the neurotransmitter serotonin binding to a nerve receptor, triggering the flow of ions across a cell membrane. Later in the clip, the flow of ions alters the membrane potential, triggering the transmission of a nerve impulse. This animation is part of a sequence showing the effects of serotonin in the brain and nervous system. Serotonin is an important neurotransmitter in the brain. A lack of it has been shown to cause depression. It is this property which has led to the development of the SSRI (selective serotonin reuptake inhibitor) antidepressants.