Parasitism is a symbiosis relationship in which two organism lives together but only one is benefited and other harm in any means. Toxoplasma is, in this case, parasite which is benefited while cats are host and harmed in this relationship.
Degree and chances of harm or benefit do not defines the symbiosis relationship between two organism. Cats are rarely harmed but still harmed in this relationship.
The human brain is the command center for the human nervous system. It receives signals from the body's sensory organs and outputs information to the muscles.
