Anatomy of the Brain


Lt Col Reynolds
The brain is an incredibly complex organ, and what the brain does is truly amazing. The brain is the body’s computer. It stores memories and controls thoughts, emotions, and all of the body’s movements. Dr. Green, can you tell us more about how the brain does these remarkable things?

Dr. Green
Certainly, Dr. Reynolds. Everything we know and everything we do is filtered, analyzed, and organized by the brain. The brain controls our personalities, our attitudes, our feelings and attractions – pretty much all the things that make us who we are. The brain also communicates with all the organs and muscles in the body, from telling the heart to beat – a function of the brainstem – to making our legs move when we want to run – a function of the motor cortex. Different parts of the brain are responsible for different things.

A healthy adult brain weighs about two and a half to three pounds, and is located inside the skull, which protects the brain from injury. Inside the skull, three thin, protective layers called the meninges cover the brain. The space between the meninges and the brain is filled with a clear liquid called cerebral spinal fluid. This fluid works to keep the central nervous system healthy. 

The brain constantly sends and receives signals from all over the body. The body then uses these signals to do things like think, move, talk, see, and understand. These signals also control personality, mood, and behavior. Each part of the brain has a specific job and links with other parts of the brain to do more difficult tasks.

The most basic functions of the brain, such as the ones that control your heartbeat and breathing, are governed by the brainstem, which is the innermost part of the brain. Further outward, more complicated functions, such as emotions and memories, are controlled by the limbic system. Autonomic nerves, which regulate internal organs such as the stomach and intestines, and the endocrine system, which includes all the body’s hormone-producing glands, are also controlled by the limbic system. The most complex functions, such as reasoning and decision-making, are controlled at the outermost level in the cerebrum.

The cerebrum is the largest part of the brain. It has a wrinkled surface of alternating “hills,” known as gyri, and “valleys,” known as sulci. The cerebrum is divided into two halves, known as the left and right hemispheres. Each hemisphere of the cerebrum is divided into four sections, called lobes. These lobes are known as the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. 

At the back of the brain beneath the occipital lobes, is the cerebellum. Like the cerebrum, the cerebellum is divided into two halves, called hemispheres. The main job of the cerebellum is to control, regulate, and coordinate movement, posture, and balance.