This article is about the brains of all types of animals, including humans.
For information specific to the human brain, see Human brain. For other uses, see Brain (disambiguation).A brain floating in a liquid-filled glass jar. Yellowing of the handwritten labels on the jar give the object an antique appearance.
A chimpanzee brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell. The brain of a vertebrate is the most complex organ in its body. In a typical human the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons,[1] each connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.