The nervous systems of animals are typically divided into two parts: a brain in the head and either a ventral nerve cord or a spinal cord in the body. Each plays a role in helping the animal to navigate and interact with its environment. The brain combines information from a number of sources – including the senses, contextual information and the internal state of the animal – to select an appropriate behavior. The ventral nerve cord then coordinates the activity of motor neurons to perform the particular action selected by the brain.