 
The nervous system includes the brain, spinal cord, and a complex network of nerves. This system sends messages back and forth between the brain and the body.The brain controls all the body's functions. The spinal cord runs from the brain down through the back. It contains threadlike nerves that branch out to every organ and part of the body. The nervous system is made up of the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves running throughout the body). The Central Nervous System Brain 
The brain controls how we think, learn, move, and feel. It is protected by the skull bones, and is cushioned by layers of membranes (called meninges) and cerebrospinal fluid. The fluid flows through hollow spaces in the brain called ventricles. The brain is like a central computer that controls all the body's functions. It lets us think and feel, learn and remember, and lets us move and talk. It also controls things we're less aware of, like the beating of our hearts and the digestion of food. The brain sends its messages back and forth with the body through the spinal cord. Spinal Cord 
The spinal cord carries messages back and forth between the brain and the nerves that run throughout the body. It is protected by bony vertebrae, a set of ring-shaped bones, and is also cushioned by layers of membranes (called meninges) and cerebrospinal fluid that flows around the spine in the spinal column. The cerebrospinal fluid not only protects the brain and central nervous system, but nourishes them and takes away waste products. The Peripheral Nervous System The peripheral nervous system includes the nerves that run throughout the whole body. Some kinds of messages begin in the eyes, ears, nose, tongue, and skin and move to the brain. Other kinds begin in the brain and then move to other parts of the body. For example, if you touch something hot, the message goes from your hand to your brain. Then your brain allows you to think about what is happening and sends messages to your muscles to move your hand away from the heat. The peripheral system is at work all the time, even when we sleep. It sends messages to the heart to keep it beating, to the muscles that we use for breathing, and to the digestive system to keep food moving along. The peripheral nervous system has two parts: The somatic system controls actions that we do by choice (voluntarily), like walking, eating, or playing an instrument. The autonomic system controls processes that happen automatically (involuntarily), like breathing, digestion, sweating, and shivering. There are two parts to this system: The sympathetic nervous system gets the body ready to react quickly to stressful or scary events. The parasympathetic nervous system controls body functions that happen all the time. 
The nervous system uses tiny interconnected cells called neurons to send messages back and forth from the brain, through the spinal cord, to the nerves throughout the body. Billions of neurons work together to create a communication network. Different neurons have different jobs. For example, sensory neurons send information from the eyes, ears, nose, tongue, and skin to the brain. Motor neurons carry messages away from the brain to the rest of the body to allow muscles to move. These connected neurons are responsible for the way we think, learn, move, and feel, and they regulate all aspects of how our bodies work. |