In vertebrate species it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to every other part of the body.

Only a few invertebrates such as sponges, jellyfish, adult sea squirts and starfish do not have a brain; diffuse or localised nerve nets are present instead.

The brain is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance,taste, and smell. The brain is the most complex organ in a vertebrate's body. In a typical human, the cerebral cortex (the largest part) is estimated to contain 15–33 billion neurons, each connected by synapses to several thousand other neurons.

Much of the size of the human brain comes from the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning,reasoning, and abstract thought. The area of the cerebral cortex devoted to vision, the visual cortex, is also greatly enlarged in humans compared to other animals.

The mind is the faculty of a human being's reasoning and thoughts. It holds the power of imagination, recognition, and appreciation, and is responsible for processing feelings and emotions, resulting in attitudes and actions.

There is no universally agreed definition of what a mind is and what its distinguishing properties are, although there is a lengthy tradition of inquiries in philosophy, religion, psychology, and cognitive science.

Neurology (from Greek: νεῦρον, neuron, and the suffix -λογία -logia "study of") deals with the diagnosis and treatment of all categories of conditions and disease involving the central and peripheral nervous system (and its subdivisions, the autonomic nervous system and the somatic nervous system); including their coverings, blood vessels, and all effector tissue, such as muscle. Neurological practice relies heavily on the field of neuroscience, which is the scientific study of the nervous system.

The site is a public information initiative of The Kavli Foundation, the Gatsby Charitable Foundation, and the Society for Neuroscience, all leading global nonprofit organizations working to advance brain research. Leading neuroscientists from around the world form the BrainFacts.org editorial board.

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Mental disorders are common. You may have a friend, colleague, or relative with a mental disorder, or perhaps you have experienced one yourself at some point. Such disorders include depression, anxiety disorders, bipolar disorder, attention deficit hyperactivity disorder (ADHD), and many others.