Martha V. Gold - Learning about the Nervous System

The Central Command Center

The nervous system is made up of the brain, the spinal cord, and nerves. It is responsible for telling the heart to beat, the lungs to breathe, and the muscles to move. The brainthe central command centerprocesses everything from understanding a teachers instructions to enjoying a piece of chocolate cake. Discover more about how this remarkable system plays a part in virtually every aspect of the human body.

About the Author

Martha V. Gold is a former journalist and educator. She now works in education technology at a small private college in western New York.

What do the following activities have in common?

• Running to catch a bus
• Breathing
• Figuring out how to put together a puzzle
• Jerking your hand away from a hot pan
• Swallowing food

Each is made possible by the nervous system, which controls the bodys internal functions. The nervous system also directs our bodys voluntary and involuntary actions. In fact, every task the body performs involves the nervous system. The endocrine system also controls certain body functions. The two systems work together.

The main parts of the nervous system are the central nervous system (CNS) and the peripheral nervous system.

The central nervous system is the most complex collection of matter that exists. It consists of the brain and the spinal cord. The brain is a spongy mass of pinkish-gray tissue that looks like a large walnut. It is divided into two halves that lie on the left and the right sides of the head. The halves are called hemispheres. A thick band of nerve fibers called the corpus callosum connects the halves.

An adult brain weighs about 3 pounds (1,300 to 1,400 grams). A newborn babys brain weighs slightly more than three-quarters of a pound (340 to 400 grams).

The skull covers the brain and protects it. Three layers of tissue called meninges lie between the brain and the skull and shield the brain from harm. The outer layer of the meninges is called the dura mater. This tough, thick layer keeps the brain in place. The inner layer, the pia mater, lies closest to the brain. The center layer is called the arachnoid.

Spaces in the brain called ventricles contain a clear liquid. This liquid, the cerebrospinal fluid, bathes the brain, surrounding it and protecting it from injury. The fluid keeps the brain afloat inside the skull. This takes the pressure off the base of the brain.

The brain serves as the central command center for the entire body. It controls every body function, from digesting food to throwing a ball to understanding language. The brain is divided into three basic parts: the cerebrum, the brain stem and related systems, and the cerebellum. The cerebrum is the largest part of the brain. The cerebral cortex, the outer layer of the cerebrum, carries out many of the brains tasks such as thinking, understanding language, and reasoning. Billions of nerve cells, also called neurons, are crammed into this thin, wrinkled layer of the brain. The motor cortex, a thin strip located in the cerebral cortex, is responsible for voluntary movement. When a person reaches for a glass of juice, the motor cortex commands the muscles in the arm and hand to close around the glass and lift it from the table.

THE BRAIN

Beneath the cerebrum lie several structures that control involuntary or automatic body functions. The thalamus, the section directly under the cerebrum, lies deep in the core of the brain. It looks like a barbell. It has two oval masses, one inside each half, that are joined by a bridge. The thalamus sorts out information from four of the senses: sight, hearing, taste, and touch. It sends signals related to these senses to the cerebral cortex. Messages relating to smell, unlike the other senses, bypass the thalamus and go directly to the cerebral cortex.

The tiny hypothalamus occupies an area just below the thalamus at the base of the brain. Though only the size of a thumbnail, it has several big jobs. The hypothalamus acts like a central computer that sends orders to other computers. It works with the nervous system and the endocrine system to keep the body functioning smoothly.

The endocrine system, like the nervous system, relays instructions to parts of the body. It does this by releasing hormones that tell the body to do certain things, such as convert food into energy. Hormones are chemicals released by glands and carried by the blood.

The hypothalamus works with other parts of the nervous system to make the body react to strong emotions such as rage, fear, and pleasure. If a person has a nightmare or sees an angry dog, the hypothalamus tells the heart to beat faster and the lungs to take shallow, quick breaths. The hypothalamus also regulates body temperature and controls hunger and thirst.

The brain stem forms a stalk that runs from the center of the brain. It contains the midbrain, the pons, and the medulla. These brain parts control breathing, heart rate, blood pressure, pupil dilation, and the vomiting reflex, among other things. They work with the cerebellum to control muscle tone. This region also works with the motor cortex to control voluntary movement.

The amygdala and the hippocampus lie below the brain stem. These are part of the limbic system, a group of structures that control emotions. The two small, almond-shaped structures of the amygdala are made up of nerve cells. This part of the brain processes and responds to sensory information from the cerebral cortex. When a perfume reminds you of your mother, the amygdala is at work. Short-term memories are stored in the hippocampus. The cerebral cortex is believed to store long-term memory.

In the back of the brain lies the cerebellum, often called the little brain. With two halves each the size of a tennis ball, it looks like a small cerebral cortex. This is the second largest part of the human brain. It coordinates complex movements such as walking. The cerebellum then stores the information about the movement. When a person rides a bicycle or learns to play the piano, the motor cortex uses this stored information to tell the muscles involved to contract and relax as needed.

The cerebellum coordinates complex tasks such as learning to play a musical instrument, then stores the information.

The second part of the central nervous system, the spinal cord, lies just below the brain stem. It is made up of nerve fibers. These fibers pass information from the rest of the body to the brain and from the brain to muscles and nerve cells. The spinal column or backbonea series of hollow bones called vertebrae that are linked togethersurround the spinal cord and protect it. Small disks of cartilagelike tiny pillowsseparate the vertebrae. Ligaments, tough bands of tissue, hold the vertebrae in place.