Weighing in at an average of 3 pounds and containing more than 100 billion nerve cells called neurons, the human brain is one of the largest and most complex human organs. Composed of fatty tissue and protein, the brain is not only the seat of intelligence and personality, but also controls voluntary and involuntary movements of the body. The brain is encased within the skull, or cranium, and is surrounded by the meninges, a protective layer of tissue made up of three membranes. Four main parts comprise the brain: the cerebrum, the cerebellum, the diencephalon, and the brain stem. The brain is also divided into two hemispheres separated by the corpus callosum and into four lobes: frontal lobes, parietal lobes, temporal lobes and occipital lobes.
The cerebrum is the largest part of the brain, and includes the cerebral cortex--the wrinkled surface of the brain. The cerebral cortex is more highly developed in humans than in any other animal, and it is in the cerebral cortex that thinking and voluntary movement originate. The cerebellum is the second largest part of the brain, and is located at the back of the brain beneath the cerebrum. The cerebellum governs muscle movement and balance. The diencephalon is located in the brain's core, and is subdivided into the thalamus and the hypothalamus. The hypothalamus controls hormones secreted by the pituitary gland which regulate growth and instinctive behaviors and some emotional responses. The thalamus helps direct nerve impulses from the body to other regions of the brain. The brain stem is located at the bottom of the brain and contains the pons and the medulla oblongata. It is the brain stem that controls crucial and often unconscious body activity such as breathing and heart rate.
The brain's frontal lobes carry on problem solving, coordinated muscle movements, and judgment and prioritization. The parietal lobes process sensations such as taste and touch, and carry on processes involved in reading, arithmetic, and handwriting. The temporal lobes process memory, hearing and language; it is in the temporal lobes that the hippocampus and amygdala are located. The hippocampus converts information from short-term memory to long-term memory, and the amygdala is responsible for emotion, learning, and response to stimulations. Both the amygdala and the hippocampus are part of the limbic system. The occipital loves process visual information.