The brain is a soft, spongy mass of tissue. It is protected by:

• The bones of the skull
  
  
• Three thin layers of tissue (meninges)
  
  
• Watery fluid (cerebrospinal fluid) that flows through spaces between the meninges and through spaces (ventricles) within the brain

This picture shows the brain and nearby structures.

The brain directs the things we choose to do (like walking and talking) and the things our body does without thinking (like breathing). The brain is also in charge of our senses (sight, hearing, touch, taste, and smell), memory, emotions, and personality.

A network of nerves carries messages back and forth between the brain and the rest of the body. Some nerves go directly from the brain to the eyes, ears, and other parts of the head. Other nerves run through the spinal cord to connect the brain with the other parts of the body.

Within the brain and spinal cord, glial cells surround nerve cells and hold them in place.

The three major parts of the brain control different activities:

• Cerebrum: The cerebrum uses information from our senses to tell us what is going on around us and tells our body how to respond. It controls reading, thinking, learning, speech, and emotions.
  
  The cerebrum is divided into the left and right cerebral hemispheres. The right hemisphere controls the muscles on the left side of the body. The left hemisphere controls the muscles on the right side of the body.
  
  
• Cerebellum: The cerebellum controls balance for walking and standing, and other complex actions.
  
  
• Brain stem: The brain stem connects the brain with the spinal cord. It controls breathing, body temperature, blood pressure, and other basic body functions.

This picture shows the major parts of the brain.

Glossary Terms

The part of the brain that is connected to the spinal cord.

The portion of the brain in the back of the head between the cerebrum and the brain stem. The cerebellum controls balance for walking and standing, and other complex motor functions.

One half of the cerebrum, the part of the brain that controls muscle functions and also controls speech, thought, emotions, reading, writing, and learning. The right hemisphere controls the muscles on the left side of the body, and the left hemisphere controls the muscles on the right side of the body.

The fluid that flows in and around the hollow spaces of the brain and spinal cord, and between two of the meninges (the thin layers of tissue that cover and protect the brain and spinal cord). Cerebrospinal fluid is made by tissue called the choroid plexus in the ventricles (hollow spaces) in the brain. Also called CSF.

The largest part of the brain. It is divided into two hemispheres, or halves, called the cerebral hemispheres. Areas within the cerebrum control muscle functions and also control speech, thought, emotions, reading, writing, and learning.

Any of the cells that hold nerve cells in place and help them work the way they should. The types of glial cells include oligodendrocytes, astrocytes, microglia, and ependymal cells. Also called neuroglia.

The three thin layers of tissue that cover and protect the brain and spinal cord.

A type of cell that receives and sends messages from the body to the brain and back to the body. The messages are sent by a weak electrical current. Also called neuron.

A group or layer of cells that work together to perform a specific function.

A fluid-filled cavity in the heart or brain.