Dopamine is a brain chemical called a neurotransmitter that carries signals between nerve cells and helps the brain perform critical functions. Dopamine helps the brain control motor functions and movement and possibly to perform other functions related to mood.
An imbalance or shortage of dopamine can cause brain dysfunction and disease. For example, in Parkinson's disease, underproduction of dopamine interferes with the transmission of signals directing movement. This can cause tremors, or shaking, often in a hand, arm, or leg as well as slow, limited movement (bradykinesia), especially when the person tries to move from a resting position.