Brain
The brain is the organ of the main control center for the body. It receives information through the senses from both inside and outside the body. It analyzes this information and then sends a message to the body that controls its functions and actions. The brain remembers past experiences, and is a source of thought, mood, and emotion. In animals, the brain, the central control of the spinal cord system, is responsible for behavior. The brain is located in the head, protected by skulls and almost with sensory devices for sight, hearing, balance, taste and odor. Whilst all vertebars have brains, most invertebrates either have a central brain or a set of isolated ganglia. Some animals like cnidarian and echinoderm have no central brain, but have a separate nervous system, while animals such as sponges are absent in the brain and nervous system altogether. The brain can be very complicated. For example, the human brain contains about 23 billion neurons, each with more than 10,000 other neurons.