The surface of the brain, known as the cerebral cortex, is very uneven, characterized by a distinctive pattern of folds or bumps, known as gyri (singular: gyrus), and grooves, known as sulci (singular: sulcus), shown in. Therefore, the lower on the spine damage is, the fewer functions an injured individual loses. When the spinal cord is damaged in a particular segment, all lower segments are cut off from the brain, causing paralysis. The spinal cord is protected by bony vertebrae and cushioned in cerebrospinal fluid, but injuries still occur. In matters of survival, the spinal reflexes allow the body to react extraordinarily fast. Seconds are saved, because messages don’t have to go the brain, be processed, and get sent back. The signal passes from the sensory nerve to a simple processing center, which initiates a motor command. When a sensory message meets certain parameters, the spinal cord initiates an automatic reflex. Withdrawal from heat and knee jerk are two examples. Some sensory messages are immediately acted on by the spinal cord, without any input from the brain. Messages travel to and from the brain through every segment. Sensory nerves bring messages in motor nerves send messages out to the muscles and organs. Nerves branch out from the spine at each vertebra. Each segment is connected to a specific part of the body through the peripheral nervous system. The spinal cord is functionally organized in 30 segments, corresponding with the vertebrae. In the opposite direction, the spinal cord ends just below the ribs-contrary to what we might expect, it does not extend all the way to the base of the spine. The top of the spinal cord merges with the brain stem, where the basic processes of life are controlled, such as breathing and digestion. It not only routes messages to and from the brain, but it also has its own system of automatic processes, called reflexes. The spinal cord is like a relay station, but a very smart one.
It can be said that the spinal cord is what connects the brain to the outside world. In this section, we discuss the overall organization of the brain and the functions associated with different brain areas, beginning with what can be seen as an extension of the brain, the spinal cord. Each lobe is associated with certain types of functions, but, ultimately, all of the areas of the brain interact with one another to provide the foundation for our thoughts and behaviors. It is a bilateral, or two-sided, structure that can be separated into distinct lobes.
The brain is a remarkably complex organ comprised of billions of interconnected neurons and glia.
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