Brain (Inferior View)

Click to View Larger Image

The brain is a jelly-like substance, which in adults weighs about three pounds. It is divided into three parts: the brain stem, which is an extension of the spinal cord, the forebrain (which consists mainly of the cerebrum), and the cerebellum. The brain's surface lies in rather ugly, wrinkled folds. Traditionally referred to as one's gray matter, it does, indeed, contain gray nerve cell bodies that surround a smaller mass of white nerve fibers. These fibers are protected by a buffer zone, including the cerebrospinal fluid and three meninges, beneath the cranial bones; which themselves enclose the brain and consist of one frontal bone, two parietals, two temporals, one occipital, one sphenoid, and one ethmoid bone. Only these pools of fluid and the skull protect the brain from the bumps and grinds of daily living, which would damage this fragile organ, and critically so, since our brain stops growing when we are about 15 years old.

The forebrain and cerebellum are divided into two hemispheres, which are linked by a thick band of nerve fibers. The frontal brain is made up of two parts: the left hemisphere, which influences logic and reasoning and controls the right hand, and the right hemisphere, which influences imagination, spatial thinking (artistic appreciation and creativity), and controls the left hand. For instance, when a professional musician has a stroke that damages the right hemisphere of his brain, his musical ability is often impaired; when the damage is to the left hemisphere, the loss of this ability is less common. The limbic system, which lies at the base of the frontal brain, connects to the spinal cord and is the emotional brain that controls all our instincts of survival.

The aforementioned hemispheres of the brain have areas, called lobes, that perform specific functions. For example, the occipital lobe controls vision. Other lobes control touch and pressure sensation, balance and coordination, and muscle movements. Speech and writing are controlled by the area in the frontal lobe of the dominant hemisphere. Given all these roles, the brain requires large amounts of stored energy for thinking. This is why you may feel the same exhaustion with intense thought processing as you do with a physical workout. Yet it is thanks to the brain that we are able to think, reason, love, forgive, create, and remember, as well as to survive through automatic processes such as breathing and digesting.