To understand what happens when the brain is injured, it is important to know what a healthy brain is made of and what it does.
The brain is the hub of the central nervous system. It feels soft and weighs about three pounds. The brain is enclosed in protective bone called the skull. The brain is held together by three layers of tissue called the dura, pia, and arachnoid membranes. Between the pia and arachnoid membranes is the subarachnoid space, through which a network of arteries and veins carries blood back and forth between the brain and heart.
The brain is made of neurons (nerve cells) which form pathways or tracts that route throughout the brain. These nerve tracts carry messages to various parts of the brain (sensory) and away from the brain (motor) to different parts of the body. The brain uses those messages to perform functions. Each part of the brain serves a specific function and links with other parts of the brain to form more complex, coordinated functions. Examples of these functions include breathing, heart rate, digestion, and elimination; thinking, talking, moving; personality; behavior; and sight, hearing, taste, smell, and touch.
When a brain injury occurs, the functions of the neurons, nerve tracts, or sections of the brain may be affected. If the neurons and nerve tracts are damaged, the nerve tracts may have difficulty or be unable to bring messages to and/or from the brain. A brain injury can change the way a person thinks, acts, feels, and/or moves. It can change internal body functions like breathing, sleeping, and pain. These changes may be temporary or permanent and may lead to partial impairment or complete inability to perform the functions that those damaged parts of the brain performed before the TBI.