Roughly 1.4 kilograms of soft tissue inside the skull generate every thought, sensation, and deliberate movement. The brain is the central organ of the nervous system, composed of neurons, glia, blood vessels, and extracellular matrix arranged in highly organized circuits.

Its surface is dominated by the folded cerebral cortex, while deeper structures handle memory, emotion, hormone control, and basic life support. Sensory information streams in, is transformed and integrated, and ultimately produces commands that leave via the spinal cord and cranial nerves. The brain also maintains homeostasis and generates the internal experiences we call consciousness and self.

Protection comes from the skull, meninges, and blood-brain barrier. Despite this armor the organ remains vulnerable to injury, infection, vascular events, and degenerative disease. Mapping its connections and dynamics continues to occupy large scientific efforts worldwide.

• Central organ of the nervous system
• Generates cognition, emotion, and behavior
• Highly organized into specialized regions
• Protected yet vulnerable to many insults