Weighing only 3 pounds, the brain is extremely complex and made up of billions of continuously interacting cells working at lightning speed.
Divided into many regions that control specific functions, the different areas of the brain are highly organized, specialized, and intricately interconnected.
In most people, the brain does not fully mature until the mid-20's, according to numerous recent studies.
The image to the left shows the neurons in the brain signalling each other. The mists of color show the flow of important molecules like glucose and oxygen. Image courtesy of NIGMS/artist Kim Hager at the Univ of California, and neurobiologist Neal Prakash, UCLA.
The brain is divided into the cerebrum, brainstem, and cerebellum:
- Cerebrum - The largest and uppermost part of the brain, the cerebrum controls many high level functions: reasoning, judgment, learning, problem solving, emotions, movement, temperature, touch, vision and hearing.
- Hemispheres: The cerebrum
is split into two halves, the left and right hemispheres. The two hemispheres appear to be mirror images of each other, but they are very different. The right hemisphere controls the movements and sensation of the left side of the body and vice versa. So if a brain tumor or stroke occurs on the right side of the brain that controls the movement of the arm, the left arm may be weak or paralyzed.
- The left hemisphere controls language, speech, skilled hand movements, and other right-sided body movements. In most people, the left hemisphere is the "dominant" hemisphere. However, in about one third of individuals who are left-handed, speech function and skilled hand control may be located on the right side of the brain, instead of the left.
- The right hemisphere controls left-sided body movements, and in most people, controls many abstract reasoning skills and spatial processing.
- Lobes: The cerebrum is divided into "lobes" which are broad regions of the brain: frontal, temporal, parietal and occipital lobes. Each hemisphere has its own set of lobes with each lobe divided into areas that serve very specific functions.
- Frontal lobes are behind the forehead and are the largest of the four lobes. They are responsible for many important functions such as voluntary movement, speech, intellect and behavior.
- Parietal lobes interpret signals received from other areas of the brain such as pain and touch. The parietal lobe also helps a person to identify objects and understand spatial relationships such as, where one's body is compared to objects around the person.
- Occipital lobes are at the back of the brain and control vision. The occipital lobe on the right interprets visual signals from the left visual space, while the left occipital lobe performs the same function for the right visual space.
- Temporal Lobes are located on each side of the brain at about ear level and are involved in memory, speech, and sense of smell.
- Brainstem - The brainstem lies in the middle of the brain and includes the midbrain, the pons, and the medulla.
The brainstem is connected to the spinal cord.
- Pons - The pons contains many of the control areas for eye and face movements.
- Medulla - The medulla is in the lowest part of the brainstem and is the most vital part of the entire brain because it contains critical control centers for the heart and lungs.
- Cerebellum - The cerebellum is at the back of the head and functions to coordinate voluntary muscle movements and to maintain posture,balance, and equilibrium. When you play the piano or hit a baseball you are activating the cerebellum.
Skull: Tough and resilient, the skull provides excellent protection for the brain
For protection, the brain is surrounded by cerebrospinal fluid (CSF), enclosed in meningeal covering, and protected inside the sturdy skull. Further cushioning is provided by the fascia and muscles of the scalp.
The Nervous System consists of the Centeral Nervous System and the Peripheral Nervous System. Some diseases are limited to the CNS whereas others are related to the peripheral nervous system.
The central nervous system (CNS) consists of the brain and spinal cord.
- The spinal cord runs from the brain down through the bony spinal column. The spine contains thread-like nerves that branch off to every part of the body. Sensory nerves carry messages from the sense organs (eyes, ears, nose, tongue, and skin) to the brain for processing. The brain then sends instructions in response through other specialized nerves to the physical parts of the body, such as the muscles, that can carry out its commands.
- The brain and spinal cord are completely covered with three layers of membranes, called meninges. In between two of the layers, is the subarachnoid space, where the cerebrospinal fluid (CSF) flows. The CSF is a clear, watery substance that helps to cushion the brain and spinal cord from injury. This fluid circulates through channels around the spinal cord and brain, constantly being absorbed and replenished. It is within hollow channels in the brain, called ventricles, where the fluid is produced. The brain normally maintains a balance between the amount of cerebrospinal fluid that is absorbed and the amount that is produced.
- The peripheral nervous system (PNS) is that portion of the nervous system that is outside the brain and spinal cord.