The human brain is a complex organ composed of approximately 86 billion neurons, responsible for controlling all bodily functions, cognitive abilities, and behaviors. It is divided into three main parts: the cerebrum, which governs higher cognitive functions like thought, memory, and emotion; the cerebellum, which coordinates movement and balance; and the brainstem, which regulates vital functions such as heart rate and breathing. The brain operates through a vast network of synapses, where neurons communicate via electrical and chemical signals. It is protected by the skull and cushioned by cerebrospinal fluid.